Abstract

Cytochrome oxidase (CO) blobs are central to our understanding of the columnar organization and parallel pathways in primate and cat visual cortex. In primates, development of blobs and their relationship with other columnar features of the visual cortex begins pre-natally, before visual experience. In kittens, the supragranular layers differentiate post-natally, after eye opening, raising the possibility that visual experience may influence the development of blobs in cat V1. We have examined the development of blobs in unfolded and flattened sections through the visual cortex of normally reared, dark-reared, monocularly deprived and binocularly deprived kittens. Blobs were found in superficial layers of V1 of normally reared kittens as early as 2 weeks of age, although at this age the overall CO staining in V1 was lighter than in V2. By 6 weeks of age the blobs were adult-like. A patchy pattern of CO staining was also found in V2 of young kittens but not in adults. Visual experience was not necessary for expression of the blobs and monocularly deprived kittens had well developed blobs, indicating that strong Y cell drive is not necessary for the development of blobs in cat V1. CO blobs appear in kitten V1 very early in post-natal development and their expression is independent of visual experience, suggesting that they may be an intrinsic feature of V1 organization.

Introduction

A simple histochemical staining for the metabolic enzyme cytochrome oxidase (CO) (Wong-Riley, 1979) produces a regular pattern of darkly stained patches in the supragranular layers of the visual cortex (Horton and Hubel, 1981; Carroll and Wong-Riley, 1984; Horton, 1984; Horton and Hedley-Whyte, 1984; Murphy et al., 1990, 1991a, b, 1995). These patches, called blobs, have become an important piece in our understanding of the functioning of the visual cortex because they are associated with both the modular organization of the visual cortex (Horton, 1984; Murphy et al., 1995) and the streaming of visual information into parallel processing pathways (Zeki, 1976; Livingstone and Hubel, 1983, 1984a; DeYoe and Van Essen, 1985, 1988; Shipp and Zeki, 1985; Van Essen et al., 1992). The initial experiments suggested that the blobs may be specific to primate visual cortex, however, our studies have shown that blobs are also present in cat visual cortex (Murphy et al., 1990, 1991a,b, 1995). This finding laid the foundation for new studies of visual cortical columns (Murphy et al., 1991b, 1995; Dyck and Cynader, 1993a; Hübener et al., 1997; Shoham et al., 1997) and parallel pathways (Boyd and Matsubara, 1996, 1999) in the cat visual cortex. Together these studies have shown that blobs are not unique to primates and represent a more general feature of mammalian visual cortical organization.

CO blobs are an ideal marker of the modular organization of visual cortex because they are spatially and functionally related to a number of columnar features. In the macaque monkey visual cortex blobs are found at evenly spaced intervals along the center of ocular dominance columns (Horton, 1984, Horton and Hocking, 1996) and receptive field properties of neurons within the blobs tend to be less binocular and less orientation selective (Livingstone and Hubel, 1984a). The blobs in macaque visual cortex are also linked with low spatial frequency domains (Tootell et al., 1988, Born and Tootell, 1991) and features of the orientation preference map (Bartfeld and Grinvald, 1992; Obermeyer and Blasdel, 1993). Similar functional relationships have been shown in cat visual cortex, where blobs are associated with the underlying ocular dominance columns (Murphy et al., 1991b, 1995; Hübener et al., 1997), orientation map (Hübener et al., 1997) and low spatial frequency domains (Hübener et al., 1997; Shoham et al., 1997). The spatial precision of these relationships can be weaker in the cat. This is especially true for the spatial relationship with ocular dominance columns where blobs avoid ocular dominance borders (Hübener et al., 1997) but are not strictly centered on ocular dominance columns (Murphy et al., 1995). Perhaps this species difference in the spatial relationship with blobs reflects developmental differences in the emergence of these visual cortical columns.

In the macaque monkey both blobs (Horton, 1984) and ocular dominance columns (Rakic, 1977) emerge pre-natally, so that at birth the pattern of ocular dominance columns and their spatial relationship with blobs is already adult-like (Horton and Hocking, 1996). Furthermore, visual experience does not influence the spatial relationship between these features in macaque visual cortex (Horton and Hocking, 1997). In contrast, the cat's visual cortex is quite immature at birth. The neurons that will form the supragranular layers of cat visual cortex, where the blobs are found, are still migrating to their adult laminar position until some time between 2 and 3 weeks of age (Shatz and Luskin, 1986) and ocular dominance columns are not visible until 2–3 weeks of age (LeVay et al., 1978; Crair et al., 1998). The segregation of geniculocortical afferents into ocular dominance columns can be delayed by rearing the kitten in complete darkness (Swindale, 1981, 1988) and numerous studies have shown that the development of certain aspects of the columns in cat visual cortex is dependent upon visual experience during the critical period [for reviews see Goodman and Shatz (Goodman and Shatz, 1993) and Katz and Shatz (Katz and Shatz, 1996)]. The development of blobs in cat visual cortex, however, has not been studied previously, leaving some very basic developmental questions unanswered. At what age and in which laminae are blobs first visible? Is the expression of blobs in cat visual cortex dependent upon or modified by visual experience?

We have studied the development of CO blobs in cat visual cortex to address these questions about the emergence of this feature of visual cortical modularity. Here we report that CO blobs are first visible at 2 weeks of age and that visual experience is not required for expression of the blobs in cat visual cortex. A preliminary report included some of these data (Duffy et al., 1998a).

Materials and Methods

Animals and Rearing Conditions

The development of CO blobs was examined in unfolded and flattened sections of visual cortex from 36 animals reared with either normal visual experience (Table 1), dark-rearing, monocular deprivation or binocular deprivation (Table 2). Dark-rearing was initiated within 24 h of birth; after inspection by a veterinarian, the kittens were placed in a light-tight dark room with their mother and carefully monitored with the aid of an infrared sensitive camera. Details of the dark-rearing procedures were as described earlier (Beaver et al., 1993). Both monocular and binocular deprivation was initiated at the time of natural eye opening by suturing closed the eyelid margins. Eyelid suture was performed using aseptic surgical techniques, gaseous anaesthetic (isoflorane 0.5–5% in oxygen) for induction and maintenance of anesthesia and following procedures that have been described in detail previously (Murphy and Mitchell, 1987). All procedures were approved by the institutional animal care and use committees.

Histology

Animals were killed with a lethal injection of Euthanol (165 mg/kg sodium pentobarbital) and perfused transcardially with cold 0.1 M phosphate-buffered saline (PBS), pH 7.4 (4°C, 80–100 ml/min) until the circulating fluid was clear, followed by 2% paraformaldehyde in 0.1 M PBS (4°C) for 4 min (80–100 ml/min). The brain was then removed from the cranium, the cerebral hemispheres were resected and either one hemisphere was unfolded and flattened as described previously (Olavarria and Van Sluyters, 1985; Murphy et al., 1995) while the other hemisphere was blocked in the coronal plane or both hemispheres were unfolded and flattened. The tissue was post-fixed with 2% paraformaldehyde and 30% sucrose for 6 h. The flattened hemisphere was held between glass slides for 20 min, left free floating for 6 h, then transferred to 30% sucrose in PBS and stored overnight. The fixation protocol produced tissue that was appropriately fixed to maintain the cytostructure of the cortex while not compromising the reactivity of the tissue. Sections were cut on a freezing microtome at a thickness of 50 μm and collected in 0.1 M phosphate buffer. Flattened hemispheres were cut tangential to the pial surface while coronal sections were cut from intact hemispheres.

Sections were mounted on gelatin-coated glass slides, allowed to air dry and then reacted (5–7 h incubation at 40°C) following standard histochemical procedures for CO staining (Horton, 1984; Murphy et al., 1995). All sections from an animal were reacted together for the same incubation period. Stained sections were dehydrated and defatted, coverslipped with DPX (Aldrich, Milwaukee, WI) and then allowed to air dry before photographing. Computer images of CO stained flat sections through the supragranular layers of the visual cortex were obtained by scanning each section with a high resolution flatbed scanner (Agfa Arcus II; Agfa, Germany). The same scanning parameters were used for all hemispheres to facilitate quantitative analyses and contrast measures were made from the raw scanned images. The figures were constructed by converting the scanned image into gray levels and the contrast was adjusted with the levels tool using Photoshop (Adobe Inc., San Jose, CA) for accurate reproduction of the pattern of CO staining.

Quantitative Analysis

CO blobs were identified as more darkly stained patches compared with interblob regions and the optical contrast between blobs and interblobs was quantified for each hemisphere by measuring the average optical staining intensity of blob and interblob regions from the raw scanned images. The contrast measurements were calculated using the following formula:

Blob-to-interblob contrast = (blob staining intensity – interblob staining intensity)/(blob staining intensity + interblob staining intensity)

This contrast measurement was used as it is not influenced by differences in overall staining intensity at different ages during development. All optical intensity measurements from blob and interblob regions were taken from the central visual field representation of each hemisphere.

Results

In adult cats there is a distinctly patchy pattern of CO staining, the blobs, throughout the full tangential extent of sections passing through layers 2/3 of the visual cortex (Fig. 1). This regular pattern of CO blobs was found in all of the adult hemispheres and the range of blob spacings for the four hemispheres studied was ~425–1050μm (Table 1). The blobs appear somewhat more distinct in the portion of the visual cortex representing the central visual field, a characteristic that has also been reported for the pattern of ocular dominance columns (Anderson et al., 1988). Finally, there was no obvious pattern to the CO staining in V2 of adult cats and in comparison with V1 the overall staining intensity of V2 was somewhat lighter. These characteristics of the CO blobs in V1 and CO staining in V2 of adult cats are very similar to our previous reports (Murphy et al., 1990, 1991a,b, 1995).

Normal Post-natal Development of CO Blobs

At all ages studied and in all tangential sections CO staining in the visual cortex was darker than the surrounding areas and clearly revealed the 2-dimensional (2D) ovate shape of the visual cortex. Even in the youngest animals studied (P7–P12) the 2D shape of the visual cortex was readily distinguished as a region of darker CO staining compared with the surrounding areas (Fig. 2). Within V1, CO staining in the youngest animals was not obviously patchy. Local variations in CO staining were found in V1, but were unlike the pattern of blobs since they did not align in adjacent sections. Thus, at P7–P12 we were not able to distinguish a regular pattern of patchy CO staining that was consistent with the presence of blobs in V1, possibly because of the immature state of the superficial layers of V1 at this stage in development (Shatz and Luskin, 1986).

A difference in the intensity of CO staining between V1 and V2 was apparent in the youngest kittens and continued to be visible in all kittens examined in this study (1–6 weeks of age). In flattened sections a band of darker CO staining was present immediately lateral to V1 (Fig. 2). This region is consistent with the location of V2, but it can be difficult to accurately distinguish the lateral border of V1 in CO stained flattened sections. We compared adjacent coronal sections stained for either CO activity or Nissl substance to determine the location of the dark band of CO staining.The darker CO staining was visible in coronal sections from kittens (Fig. 3A,B) and after comparison with Nissl stained sections it was clear that the dark band coincided with V2. This pattern of darker CO staining in V2 than V1 was found in all of the kittens, however, it was not observed in any of the adults used in this (Figs 1, 3C) or our previous studies (Murphy et al., 1990, 1991a, 1995).

Blobs were first faintly visible at 2 weeks of age in V1 of seven of the eight hemispheres examined, although the contrast of the blobs in the two hemispheres was extremely low. By 2.5 weeks of age the 2D pattern of CO blobs was quite distinct (Fig. 4), although in these young animals the contrast of the blob-to-interblob staining intensity was only ~50–60% of the contrast found in adults (Table 1). The blobs were packed closely together in 2–2.5 week old animals, probably because there is still substantial post-natal growth of the cortex after this age, with the visual cortex almost doubling in area between 2 weeks of age and adult (Duffy et al., 1998b). Because of the close packing and the low contrast of the blobs at 2–2.5 weeks of age it was not possible to reliably identify all of the blobs in a region, so we were not able to quantify the spacing of the blobs. We were, however, able to characterize a number of other features of the staining pattern of these nascent blobs in kitten V1. Blobs were present throughout the full tangential extent of V1. We did not note any tendency for them to appear at one location before another, although the blobs were somewhat darker along the medial portion of V1. This gradient of CO staining was also apparent in coronal sections, where the staining in V1 was somewhat lighter around the crown of the posterolateral gyrus and darker down the medial bank in very young kittens (Fig. 3A). The radial extent of the blobs was assessed using blood vessel landmarks to align adjacent tangential sections and following the staining pattern for individual blobs through a series of sections. The regular patchy pattern of CO blobs was found in tangential sections from ~250 to 600 μm below the pial surface (Fig. 5). These depths correspond with the laminar location from just below the zone of compact cells at the top of the developing layers 2/3 and down to the upper half of layer 4. Blobs were most distinct ~400–550 μm below the surface; at 2–2.5 weeks of age this corresponds with the bottom of layer 3 and upper half of layer 4.

In normal adult cats blobs are present in sections through layers 2/3, whereas the staining pattern within layer 4 is uniform (Murphy et al., 1995). A patchy pattern is found in layer 4 only following deprivation of vision in one eye in adult cats (Wong-Riley, 1979, Wong-Riley and Riley, 1983; Murphy et al., 1995). Our observation of patchy CO staining in layer 4 of normal young kittens is at variance with the pattern observed in adults and raises questions concerning its interpretation. Therefore, we wanted to explore why we found patchy CO staining in layer 4 of very young kittens. Prompted by a recent report (Crair et al., 1998) of a contralateral dominance in the ocular dominance map in very young kittens, we examined whether such a bias may have contributed to the pattern of CO staining observed in the young kittens. If the patchy pattern of CO staining found in layer 4 at the youngest ages (2–2.5 weeks of age) was a result of dominance by the contralateral eye in the geniculocortical pathway then the A lamina of the LGN should be stained darker for CO activity. There was no difference in the density of CO staining in the A and A1 laminae (both were darkly stained), furthermore, the staining was very light in the contralaterally dominated C laminae (Fig. 6). These results indicate that it is unlikely that the pattern of CO blobs observed in V1 of young kittens simply reflects a contralateral eye dominance in the geniculocortical pathway.

Having established that blobs first appear at ~2–2.5 weeks of age in normal kittens (Fig. 7AD) we went on to examine their development during the early portion of the critical period. A distinct pattern of CO blobs was already present by 3 weeks of age (Fig. 7E,F). An adult-like pattern of CO blobs was found throughout V1 by 4 weeks of age (Fig. 8) and the contrast of the blob-to-interblob staining intensity had increased to 76% (SEM = 12.4) of adult levels (Table 1). We were able to analyze the spacing of blobs at 4 weeks of age because of the increased blob-to-interblob contrast as well as the fact that most of the areal growth of kitten visual cortex occurs before 4 weeks of age. The range of center-to-center blob spacing was ~300–900 μm at 4 weeks of age (Table 1). To compare these measurements with those observed in adults it was necessary to scale the measurements for the growth of V1, since at 4 weeks of age V1 is ~80% of the adult size (Duffy et al., 1998b). The scaled range of blob-to-blob spacing (~370–1125 μm) was very similar to that reported in our previous study of adult cats (350–1000 μm) (Murphy et al., 1995), as well as the spacing range measured in the adults in this study. The radial extent of the blobs was 300 μm, extending ~250–550 μm below the pial surface. This placed the blobs largely within layer 2/3 and extending into the top portion of layer 4. By 6 weeks of age the blobs were indistinguishable from adults (Fig. 9). The tangential pattern, radial extent and blob-to-interblob contrast (Table 1) observed at 6 weeks of age were not different from adults and when the spacing was scaled for growth it too fell within the range observed in adults.

CO Staining in Kitten V2

In addition to the blobs in V1, an obvious periodic pattern of dark CO staining was observed in V2 of 3 and 4 week old animals (Figs 8A, 10) but was less obvious at 6 weeks. The dark patches of CO staining were more prominent in the posterior aspect of V2 and were much larger than the blobs. We compared aligned sections to follow the radial extent of the V2 patches. The radial extent of the patches spanned ~400 μm, from ~300 to 700 μm below the pial surface, and clearly extended much deeper than the blobs in V1. We were unable to distinguish a consistent shape or pattern to the V2 patches, some of which appeared elongated in shape and oriented orthogonal to the V1/V2 border (Fig. 10A), while others were more circular in shape (Fig. 10B).

CO Blobs in Dark-reared Kittens

Since blobs were first visible in kitten visual cortex ~1 week after the eyes open we wished to determine whether visual experience was necessary for the development of blobs in cat visual cortex. To address this question we examined the pattern of CO staining in V1 of kittens reared in the dark from very shortly after birth until 3–6 weeks of age. We were interested in these ages because previous studies have indicated that visual experience is not necessary for the initial expression of columnar maps at 3 weeks of age, but is essential for maintaining cortical responsiveness and expression of the maps at 6 weeks of age (Crair et al., 1998). Blobs were obvious in two of four hemispheres from kittens dark-reared until 3 weeks of age. In these two hemispheres the blob-to-interblob contrast (~75%) (Table 2) and the pattern of the blobs was similar to that of age-matched normals. The overall intensity of CO staining increased when dark-rearing was extended and a regular patchy pattern of distinct CO blobs was found in superficial sections through V1 of all hemispheres studied from 4–6 week old dark reared kittens (Fig. 11). The blob-to-interblob contrast, radial extent and spacing of the blobs (range ~320–1000 μm) in dark-reared kittens (Table 2) were similar to those observed in normally reared animals. Thus, visual experience was not necessary for expression of CO blobs in kitten visual cortex or maintenance of blobs during the peak of the critical period. These findings suggest that the expression and arrangement of blobs may reflect innate aspects of kitten visual cortical organization.

CO Blobs in Monocularly and Binocularly Deprived Kittens

To further examine the effect of visual experience on the development of blobs we studied the pattern of blobs in the visual cortex of animals monocularly or binocularly deprived from eye opening. Monocular deprivation in kittens affects the arrangement of geniculocortical afferents serving the two eyes, with an expansion of the non-deprived eye's afferents and a shrinkage of the deprived eye's afferents to form a regular pattern of isolated patches of input to the visual cortex. Monocular deprivation did not, however, disrupt the development of blobs. A distinct pattern of blobs was found in the supragranular sections from the monocularly deprived animals (Fig. 12). The 2D pattern of blobs in monocularly deprived animals appeared similar to the pattern observed in normally reared animals, although some blobs seemed to be slightly lighter stained (Fig. 12B). This pattern is very similar to that observed in early monocularly deprived macaque monkeys (Horton and Hocking, 1997), where blobs persist over deprived eye columns but are stained somewhat lighter. The range of blob-to-blob spacing (350–1060 μm in the adult MD) and the maximum contrast of blob-to-interblob staining (Table 2) was similar to the values measured for normally reared animals.

Binocular deprivation also did not affect expression of CO blobs. All kittens deprived of visual experience by bilateral eyelid suture until either 4 or 6 weeks of age had well-developed patterns of blobs in V1 and darker CO patches in V2 (Fig. 13). The spacing of the blobs in binocular deprived kittens was not different from normals, while the contrast of the blobs was either comparable with or slightly greater than normal agematched animals (Tables 1, 2). There was no tendency for any degradation of the CO blobs when deprivation was extended to 6 weeks of age.

Development of Blob-to-interblob Contrast

Taken together, the results show that CO blobs developed very rapidly in kitten visual cortex beginning at ~2 weeks of age and that visual experience was not necessary for emergence or initial development of the blobs. These results are summarized in Figure 14, where the blob-to-interblob contrast is plotted for all of the hemispheres studied from the four rearing conditions as a percentage of the average contrast of normal adult cats. There was rapid development of the staining contrast of the blobs between 2 and 4 weeks of age, when it increased from ~45 to 75%, respectively, of the average contrast found in adult animals. By 6 weeks of age the blob-to-interblob contrast had reached adult levels. Disrupting visual experience by either dark-rearing, monocular deprivation or binocular deprivation did not reduce blob-to-interblob contrast from normal age-matched levels.

Discussion

In this study we have examined the development of CO blobs in the upper layers of kitten visual cortex and the influence of visual experience on blob development. Blobs are first visible at ~2 weeks of age in layers 2/3 and the upper half of layer 4 in kitten visual cortex. This is ~1 week after eye opening, 1 week before migration of neurons destined to form the superficial layers is complete (Shatz and Luskin, 1986) and the age at which ocular dominance columns are first visible (Crair et al., 1998). Over the next few weeks there is rapid development of the blobs and by 6 weeks of age the blobs are indistinguishable from blobs in adult visual cortex. Altering visual experience by either monocular deprivation, binocular deprivation or dark-rearing does not affect the pattern of blobs, demonstrating that visual experience is not necessary for either initial expression or early development of blobs in kitten visual cortex. This lack of dependence on visual experience is similar to the developmental situation in macaque monkeys, where an adult-like pattern of blobs is present at birth, before any visual experience (Horton and Hocking, 1996). Thus, although blobs emerge post-natally and after eye opening in kittens, the lack of influence of visual experience on their development suggests that they may reflect an innate columnar organization in the upper layers of cat visual cortex.

Methodological Considerations

Prior to our reports of blobs in adult cat V1 (Murphy et al., 1990, 1991a,b, 1995) a number of groups had attempted to demonstrate the presence of blobs in non-primate species (Wong-Riley, 1979; Horton, 1984; Price, 1985). The main technical difference between our studies of blobs in kitten or adult cat visual cortex and these earlier investigations is that we have used tangential sections from unfolded and flattened visual cortex (Olavarria and Van Sluyters, 1985), whereas earlier attempts used radial cut sections. Since our initial reports, other groups have also visualized blobs in tangential sections through cat cortex (Dyck and Cynader, 1993a; Boyd and Matsubara, 1996; Shoham et al., 1997). We looked at CO staining in radial sections but, because of the low contrast of the blobs in cat cortex, were unable to reliably identify them in the upper layers of radially cut sections. In CO stained tangential sections, however, the regular 2D pattern of blobs is readily identified, even in young kittens where the blob contrast is quite low. Furthermore, it is relatively easy to confirm that the pattern observed in any one section reflects a columnar arrangement of blobs by aligning adjacent sections using the radial blood vessels and following the pattern of CO blobs through successive supragranular sections. In our experience, sections cut tangential to the surface of the unfolded and flattened cortex provide the most sensitive technique for resolving anatomical patterns that are arrayed parallel to the cortical laminae. This is especially true when the histological image of the anatomical pattern is low contrast, as is the case for CO blobs in cat visual cortex.

CO Staining in V2

The CO staining in V2 of adult cats is relatively light and does not exhibit obvious patchiness (Murphy et al., 1995; present study), which contrasts with the pattern of thick pale–thin pale CO stripes found in monkey V2. The CO staining in V2 of young kittens is different from adults. The staining intensity of V2 is greater relative to the staining of V1 and there are patches of darker CO staining within V2 of young kittens. In some cases the patches appear elongated and oriented orthogonal to the V1/V2 border, but in other cases the patches are more circular. The V2 patches are most visible in the posterior half of V2 in kittens and may reflect functional differences in the architecture of V2 or may simply be because the flattening procedure was optimal for the posterior portion of V2. Curiously, we have never observed patchiness or darker CO staining in adult cat V2. It is not clear whether the darker CO staining in V2 relative to V1 is related to a functional difference, since the rate of maturation of physiological properties in these areas is very similar (Blakemore and Price, 1987). It may reflect the higher density of synaptic boutons on Y cell afferents to V2 of kittens (Friedlander and Martin, 1989) that could place higher metabolic demands on V2 leading to darker CO staining. The V2 patches may also be related to the arrangement of direct thalamic inputs, in particular the periodic W cell projection from the C laminae to layers 3 and 4 of V2 (Kawano, 1998), which would be similar to the thalamic projections from the C laminae to blobs in V1 (Boyd and Matsubara, 1996).

Laminar Development of Blobs

When the blobs are first visible at 2 weeks of age in kittens they are found in layers 2/3 and the top half of layer 4, whereas in adult cats the blobs are largely confined to layers 2/3 and only dip into the very top of layer 4 (Murphy et al., 1995) (see also present study). A pattern of blobs in layer 4 of kitten visual cortex has been noted previously (Dyck and Cynader, 1993a) and similar observations have been made with respect to the laminar location of blobs during early pre-natal development of macaque monkeys (Horton, 1984). At E144 in macaque monkeys, an age that coincides with the start of ocular dominance column formation (Rakic, 1977), CO blobs are visible in layers 2/3, but they are more obvious and intensely labeled in layer 4b (Horton, 1984). In contrast, in the adult macaque CO staining in layer 4b is weak and blobs in this layer are extremely faint. Thus, both cats and macaque monkeys have a transient expression of obvious blobs in layer 4 during early development. Parenthetically, blobs in human visual cortex also develop post-natally, but do not appear in layer 4 (Wong-Riley et al., 1993). Dark CO staining is strongly associated with regions receiving direct thalamic input (Horton, 1984), raising the possibility that the transient expression of blobs in the top half of layer 4 in kittens may reflect a transiently patchy organization of the geniculocortical projections to that region of layer 4. There is a patchy projection from the C laminae of the LGN (W cell and Y cell pathways) to layer 3 and the top of layer 4 in the adult cat (LeVay and Gilbert, 1976; Leventhal, 1979; Kawano, 1998), which aligns with the CO blobs (Boyd and Matsubara, 1996). Perhaps during development there is a transiently greater projection from the C laminae to layer 4 giving rise to the pattern of blobs observed in layer 4 of kittens. It is important to remember, however, that the lamination of kitten visual cortex is immature in several respects during early post-natal development (Shatz and Luskin, 1986). Migration of neurons that will form layers 2/3 is not complete until ~3 weeks of age and differentiation of the layers continues for many weeks. Thus, the appearance of blobs in the top half of layer 4 in young kittens may reflect the immature state of cortical lamination rather than a transiently patchy projection to layer 4.

Tangential Development of the Blobs

In comparison with the blobs in macaque monkey V1, the blobs in kitten and cat visual cortex are lower in contrast and are often linked together or abutting rather than isolated patches of dense CO staining. This is particularly true early in development when blobs in kitten V1 are faint and are packed very close together because the areal extent of V1 is still growing. For these reasons it is difficult to quantify the 2D pattern of CO blobs in cat visual cortex using the 2D nearest neighbor spatial statistics that have been used to characterize the 2D pattern of monkey blobs (Murphy et al., 1998). These statistics are dependent upon the identification of all the blobs within a sampling window and consequently will provide spurious results when it is difficult to identify every blob. For example, quantification of the average density will be underestimated and the average spacing will be overestimated if all of the blobs cannot be identified. Because of these problems we used a more conservative measure (the range of blob spacing) of the arrangement of the blobs that is less affected than central tendency measures if some blobs cannot be readily identified. The range of blob spacing measured in the kittens, when scaled for growth of the cortex, was very similar to the range of spacings found in adult cats. This suggests that the number of blobs in kitten visual cortex remains relatively constant throughout development and is consistent with a previous report of an approximately static number of blobs during post-natal development in monkeys (Purves and LaMantia, 1993). Qualitatively, the 2D pattern of blobs in kitten V1 becomes adult-like in appearance at ~4 weeks of age. The overall growth of visual cortex and increase in blob contrast that occurs by 4 weeks of age are significant factors in the emergence of an adult-like appearance of blobs by that age.

One advantage of viewing the complete tangential pattern of blobs is that it is possible to determine whether there is a gradient across V1 during the development of CO blobs. Although the blobs are quite faint when first visible at 2 weeks of age, they are found in all locations of V1, including representation in the monocular crescent, and appear to be equally well developed across V1. An overall gradient of CO staining is present during early development, with lighter staining in the lateral region of V1 (central visual field representation) and darker staining in the medial aspect of V1 (peripheral visual field representation and monocular crescent). This staining gradient diminishes sometime after 4 weeks of age and may be related to an initial delay in the development of the geniculocortical afferents to the lateral portion of V1 (Shatz and Luskin, 1986). There is also a tendency for the blobs to be more distinct in the region of V1 representing the central visual field; this is the same region where the ocular dominance pattern is most distinct (Anderson et al., 1988) and where there is a higher proportion of monocularly driven cells (Albus, 1975).

Influence of Visual Experience on Development of the Blobs

We found that visual experience is not required for the initial expression or early development of blobs in kitten visual cortex. Kittens reared in complete darkness have a pattern of CO blobs that is not different from normal kittens. Furthermore, when visual experience is altered by either monocular or binocular eyelid suture from eye opening it does not effect the initial development of blobs in kitten visual cortex. For two reasons we were surprised to find no obvious change in the pattern of blobs after early monocular deprivation in kittens. First, previous research suggested that blobs in cat visual cortex are dependent upon the heavy synaptic drive of Y cell geniculocortical afferents (Boyd and Matsubara, 1996). This notion is not consistent with the present results, since Y cells are preferentially affected by monocular deprivation (Sherman et al., 1972) [reviewed by Sherman and Spear (Sherman and Spear, 1982)] and yet we found very little effect of deprivation on expression of the blobs. Perhaps the initial expression of the blobs is dependent on another thalamocortical pathway. The blobs also receive direct thalamic projections from W cells (Boyd and Matsubara, 1996) and W cells are relatively unaffected by monocular deprivation (Hickey, 1980). Taken together, these results suggest that the W cell input to kitten cortex may be sufficient for expression of the blobs and that strong Y cell drive is not necessary. This is similar to the results from early monocularly deprived monkeys where the koniocellular projection to the blobs is spared and blobs are found in both deprived and non-deprived eye columns (Horton and Hocking, 1997). Second, we have shown previously that enucleation in adult cats leads to a loss of CO blob staining associated with the enucleated eye's ocular dominance columns (Murphy et al., 1995) and might have expected a similar effect after early eyelid suture. These two manipulations, enucleation and eyelid suture, however, have very different affects on the geniculocortical pathway. Enucleation silences the inputs, whereas early monocular deprivation changes the pattern of inputs to form isolated patches of inputs serving the deprived eye where the patches have the same spacing as ocular dominance columns in normal animals (Jones et al., 1996). It seems likely that these patches of geniculocortical input continue to provide sufficient input to the deprived eye's columns to maintain the metabolic activity of these blobs. This appears to be what happens following early monocular deprivation in macaque monkeys, where there is shrinkage of the deprived eye's geniculocortical inputs forming a fragmented pattern of clumps that coalesce around the CO blobs (Horton and Hocking, 1997).

Relationship to Other Patchy Markers

The patchy intracortical connections in the supragranular layers of cat cortex (Gilbert and Wiesel, 1979, 1983) follow a developmental course (Callaway and Katz, 1990) that is similar to the emergence of the blobs and is also not dependent upon visual experience (Callaway and Katz, 1991). There is a tendency for the patchy intracortical connections in primate visual cortex to form a network of blob-to-blob connections (Livingstone and Hubel, 1984b; Yoshioka et al., 1996; Yabuta and Callaway, 1998), raising the possibility that the horizontal connections in cat visual cortex also represent a similar network. Several other anatomical features are transiently patchy during development of kitten visual cortex, including adenosine receptors (Schoen et al., 1990), zinc (Dyck and Cynader, 1993a), serotonin receptors (Dyck and Cynader, 1993b), the proto-oncogene c-fos (Beaver et al., 1992, 1993) and neurons expressing the NMDAR1 subunit (Murphy et al., 1996; Trepel et al., 1998). The NMDA patches are of particular interest because of the role of NMDA receptor activation in experience-dependent modification of the developing visual cortical columns (Kleinschmidt et al., 1987; Bear et al., 1990). Although the CO blobs and NMDA patches are both found in the supragranular layers and appear at 2 weeks of age, the laminar development of these features is not the same. The NMDA patches emerge at the top of the developing cortical plate in the zone of compact cells just below layer 1 and then extend down towards the top of layer 4 (Trepel et al., 1998). In contrast, the blobs are not found in the laminar zone of compact cells but instead are most obvious in the top half of layer 4 and the bottom of layer 3 in young kittens. Expression of the NMDA patches is dependent upon binocular visual experience (Trepel et al., 1998; Duffy and Murphy, 1999), whereas expression of the blobs is independent of visual experience. Finally, these features are related to different aspects of ocular dominance columns. The blobs in cat visual cortex are functionally (Murphy et al., 1995) and spatially linked with the more monocular aspects of ocular dominance columns (Hübener et al., 1997), as well as orientation pinwheels (Hübener et al., 1997) and low spatial frequency domains (Hübener et al., 1997; Shoham et al., 1997). The NMDA patches are associated with the borders of ocular dominance columns (Trepel et al., 1998), presumably the more binocular regions, and may facilitate activity-dependent refinement of developing circuits at column borders. These differences between blobs and NMDA patches suggest that they could fill complementary niches during development of ocular dominance columns.

A Role for Blobs in Column Development?

In light of the relationship of the blobs to other patchy anatomical markers and the columnar maps in V1, it is important to consider how the metabolically more active CO blobs arise and whether they could contribute to the development of other patchy cortical features. The emergence and arrangement of blobs is not dependent upon either visual experience (Horton, 1984) (see also present study), spontaneous retinal activity (Kuljis and Rakic, 1990; Kennedy et al., 1990) or the segregation of ocular dominance columns (Kind et al., 1993). Taken together, these results point towards some type of intrinsic cortical specification of the blobs that differs from competition-driven development of cortical circuitry and may be related to factors that govern the patterning of geniculocortical afferents into ocular dominance columns in the absence of retinal activity (Crowley and Katz, 1999). Perhaps the emergence of blobs follows rules similar to those that specify the initial segregation of the magno- and parvocellular pathways (Meissirel et al., 1997) and the location of cortical areas during neurogenesis (Donoghue and Rakic, 1999). It seems possible that a periodic array of molecularly distinct cues could underlie the development of CO blobs. This still leaves open the question of a role for the blobs in the development of other columnar systems.

CO blobs are associated with reduced orientation selectivity, multiple orientations (pinwheel centers), low spatial frequency and monocular regions of ocular dominance columns. This collection of blob properties leads to relatively more frequent and sustained activation of neurons within the blobs. For example, blob neurons will tend to respond to all contours because of the reduced orientation selectivity (Livingstone and Hubel, 1984a) and the association of orientation pinwheel centers with the blobs (Obermayer and Blasdel, 1993; Hübener et al., 1997). One way to view this is that the relatively greater activity of blob neurons leads to greater metabolic demands and hence the greater CO activity. Horton discussed this issue and concluded, as have we for the reasons outlined above, that it is extremely unlikely that visually driven activity determines the 2D pattern of the blobs (Horton, 1984). Another way to consider this issue is whether patches in the cortex that have the intrinsic capacity to be more metabolically active could influence the organization of physiological properties during development and, as a result, contribute to the overall layout of the columnar systems. A recent computational model of the development of visual cortical columns has addressed this question and shown a tendency for ocular dominance column centers and orientation pinwheels to emerge near simulated CO blobs (Jones and Leyton-Brown, 1998). This is an intriguing result that provides theoretical support for the notion that blobs could contribute to the development of other visual cortical columns (Jones et al., 1991; Murphy et al., 1995).

Although the blobs emerge post-natally in kitten visual cortex, their development and arrangement is independent of the pattern of visually driven activity, suggesting that they reflect an intrinsic organization of the cortical circuitry. Furthermore, during early development there are important similarities between the emergence of blobs in both cat and macaque monkey visual cortex. These results underscore that blobs are not unique to primate visual cortex and demonstrate the importance of a second model system for comparative investigations of the significance of blobs for the development of visual cortical organization and function.

Notes

This work was supported by grants from NSERC—CIHR to K.M.M., D.G.J. and D.E.M., and an Ontario Premier's Research Excellence Award to K.M.M.

Address correspondence to Dr Kathryn M. Murphy, Department of Psychology, McMaster University, 1280 Main Street West, Hamilton, Ontario L8S 4K1, Canada. Email: kmurphy@vision.mcmaster.ca.

Table 1

CO blob measurements in normal animals

Cat no. Age (weeks) Condition Flattened hemisphere Blob contrast % of normal adult contrast Blob spacing min–max (μm) 
K173 normal left no blobs – – 
K169 1.5 normal left no blobs – – 
K170 normal left no blobs – – 
K174 normal left 0.081  54.27 – 
K176 normal right 0.096  64.32 – 
K176 normal left 0.086  57.62 – 
K168 normal right 0.071  47.57 – 
K168 normal left 0.057  38.19 – 
K144 normal right 0.037  24.79 – 
K144 normal left 0.038  25.46 – 
K177 2.5 normal right 0.089  59.63 – 
K177 2.5 normal left 0.078  52.26 – 
K171 2.5 normal left 0.075  50.25 – 
K172 normal left no blobs – – 
K175 normal right 0.074  49.58 – 
K175 normal left 0.056  37.52 – 
K145 normal right 0.067  44.89 – 
K145 normal left 0.055  36.85 – 
K178 normal right 0.123  82.41 – 
K178 normal left 0.077  51.59 – 
K146 normal right 0.114  76.38 323–892 
K146 normal left 0.067  44.89 314–943 
K167 normal right 0.138  92.46 302–806 
K167 normal left 0.133  89.11 314–820 
K198 normal left 0.176 117.92 363–727 
K198 normal right 0.138  92.46 363–818 
K5354 adult normal left 0.114  76.38 490–1045 
K5183 adult normal right 0.141  94.47 425–1000 
K5183 adult normal left 0.150 100.50 435–1015 
K5365 adult normal left 0.192 128.64 432–1040 
Cat no. Age (weeks) Condition Flattened hemisphere Blob contrast % of normal adult contrast Blob spacing min–max (μm) 
K173 normal left no blobs – – 
K169 1.5 normal left no blobs – – 
K170 normal left no blobs – – 
K174 normal left 0.081  54.27 – 
K176 normal right 0.096  64.32 – 
K176 normal left 0.086  57.62 – 
K168 normal right 0.071  47.57 – 
K168 normal left 0.057  38.19 – 
K144 normal right 0.037  24.79 – 
K144 normal left 0.038  25.46 – 
K177 2.5 normal right 0.089  59.63 – 
K177 2.5 normal left 0.078  52.26 – 
K171 2.5 normal left 0.075  50.25 – 
K172 normal left no blobs – – 
K175 normal right 0.074  49.58 – 
K175 normal left 0.056  37.52 – 
K145 normal right 0.067  44.89 – 
K145 normal left 0.055  36.85 – 
K178 normal right 0.123  82.41 – 
K178 normal left 0.077  51.59 – 
K146 normal right 0.114  76.38 323–892 
K146 normal left 0.067  44.89 314–943 
K167 normal right 0.138  92.46 302–806 
K167 normal left 0.133  89.11 314–820 
K198 normal left 0.176 117.92 363–727 
K198 normal right 0.138  92.46 363–818 
K5354 adult normal left 0.114  76.38 490–1045 
K5183 adult normal right 0.141  94.47 425–1000 
K5183 adult normal left 0.150 100.50 435–1015 
K5365 adult normal left 0.192 128.64 432–1040 
Table 2

CO blob measurements in visually deprived animals

Cat no. Age (weeks) Condition Flattened hemisphere Blob contrast % of normal adult contrast Blob spacing min–max (μm) 
C799 dark reared right no blobs – – 
C799 dark reared left no blobs – – 
C800 dark reared right 0.066  44.22 – 
C800 dark reared left 0.093  62.31 – 
C806 dark reared right 0.068  45.56 – 
C805 dark reared right 0.121  81.07 312–891 
C805 dark reared left 0.111  74.37 358–930 
C807 dark reared right 0.080  53.60 327–996 
C807 dark reared left 0.103  69.01 353–1015 
C792 dark reared left 0.176 117.92 337–937 
C794 dark reared left 0.168 112.56 319–923 
C801 dark reared right 0.107  71.69 327–985 
C801 dark reared left 0.127  85.09 337–965 
C813 dark reared right 0.169 113.23 351–996 
C804 dark reared right 0.104  69.68 454–818 
C804 dark reared left 0.106  71.02 363–909 
C802 dark reared right 0.120  80.40 360–1019 
C802 dark reared left 0.111  74.37 338–956 
K157 monocular deprivation left 0.104  69.68 – 
K164 monocular deprivation left 0.075  50.25 – 
K5255 adult monocular deprivation left 0.135  90.45 353–1061 
K196 binocular deprivation right 0.078  52.26 200–600 
K196 binocular deprivation left 0.133  89.11 300–700 
K197 binocular deprivation right 0.19 127.30 360–820 
K197 binocular deprivation left 0.22 147.40 270–640 
Cat no. Age (weeks) Condition Flattened hemisphere Blob contrast % of normal adult contrast Blob spacing min–max (μm) 
C799 dark reared right no blobs – – 
C799 dark reared left no blobs – – 
C800 dark reared right 0.066  44.22 – 
C800 dark reared left 0.093  62.31 – 
C806 dark reared right 0.068  45.56 – 
C805 dark reared right 0.121  81.07 312–891 
C805 dark reared left 0.111  74.37 358–930 
C807 dark reared right 0.080  53.60 327–996 
C807 dark reared left 0.103  69.01 353–1015 
C792 dark reared left 0.176 117.92 337–937 
C794 dark reared left 0.168 112.56 319–923 
C801 dark reared right 0.107  71.69 327–985 
C801 dark reared left 0.127  85.09 337–965 
C813 dark reared right 0.169 113.23 351–996 
C804 dark reared right 0.104  69.68 454–818 
C804 dark reared left 0.106  71.02 363–909 
C802 dark reared right 0.120  80.40 360–1019 
C802 dark reared left 0.111  74.37 338–956 
K157 monocular deprivation left 0.104  69.68 – 
K164 monocular deprivation left 0.075  50.25 – 
K5255 adult monocular deprivation left 0.135  90.45 353–1061 
K196 binocular deprivation right 0.078  52.26 200–600 
K196 binocular deprivation left 0.133  89.11 300–700 
K197 binocular deprivation right 0.19 127.30 360–820 
K197 binocular deprivation left 0.22 147.40 270–640 
Figure 1.

(A) A single unfolded and flattened section through the superficial layers of the adult cat (K5365) posterior neocortex reveals the 2D ovate extent of V1 as being more darkly stained for CO compared with the surrounding cortical regions. CO blobs are apparent throughout V1 in the supragranular layers. In adult cats the V1/V2 border is not readily identified in CO stained sections. (B) A higher magnification photomicrograph taken from the area centralis representation of the section displayed in (A) that shows the pattern of CO blobs in adult cat V1. The inset diagram outlines the low magnification section in (A) showing the border of V1 and the location of the high magnification view of the blobs shown in (B). Scale bars: A, 5 mm; B, 1 mm.

Figure 1.

(A) A single unfolded and flattened section through the superficial layers of the adult cat (K5365) posterior neocortex reveals the 2D ovate extent of V1 as being more darkly stained for CO compared with the surrounding cortical regions. CO blobs are apparent throughout V1 in the supragranular layers. In adult cats the V1/V2 border is not readily identified in CO stained sections. (B) A higher magnification photomicrograph taken from the area centralis representation of the section displayed in (A) that shows the pattern of CO blobs in adult cat V1. The inset diagram outlines the low magnification section in (A) showing the border of V1 and the location of the high magnification view of the blobs shown in (B). Scale bars: A, 5 mm; B, 1 mm.

Figure 2.

At 1 week (A) (K173) and 12 days (B) (K169) of age V1 and V2 are more darkly stained for CO activity relative to the surrounding cortical regions. Blobs are not present at these ages. The laterally adjacent V2 region is very darkly stained for CO at these ages (insets show the borders of V1 and V2). Scale bar: 5 mm.

Figure 2.

At 1 week (A) (K173) and 12 days (B) (K169) of age V1 and V2 are more darkly stained for CO activity relative to the surrounding cortical regions. Blobs are not present at these ages. The laterally adjacent V2 region is very darkly stained for CO at these ages (insets show the borders of V1 and V2). Scale bar: 5 mm.

Figure 3.

Coronally cut CO stained sections were compared with adjacent Nissl stained sections to identify the V1/V2 border. At 1 week (A) (K173) and 3 weeks (B) (K172) of age CO staining of V2 is darker than staining of V1. (C) In the adult cat (K5354) the intensity of CO staining in V1 and V2 is comparable, making the V1/V2 border very difficult to identify in CO stained sections. Scale bar: 1 mm.

Figure 3.

Coronally cut CO stained sections were compared with adjacent Nissl stained sections to identify the V1/V2 border. At 1 week (A) (K173) and 3 weeks (B) (K172) of age CO staining of V2 is darker than staining of V1. (C) In the adult cat (K5354) the intensity of CO staining in V1 and V2 is comparable, making the V1/V2 border very difficult to identify in CO stained sections. Scale bar: 1 mm.

Figure 4.

(A) An unfolded and flattened CO stained section through visual cortex of a 2.5 week old kitten (K177). A regular pattern of CO blobs is obvious throughout V1, however, the contrast between blobs and interblobs is lower than that found in adults. V2 is easily identified by the darker staining relative to V1. (B) High magnification picture taken from the section in (A) reveals low contrast, regularly spaced CO blobs. These CO blobs are tightly packed together, often appearing connected or banded because the visual cortex is substantially smaller at this age. Scale bars: A, 5 mm; B, 1 mm.

Figure 4.

(A) An unfolded and flattened CO stained section through visual cortex of a 2.5 week old kitten (K177). A regular pattern of CO blobs is obvious throughout V1, however, the contrast between blobs and interblobs is lower than that found in adults. V2 is easily identified by the darker staining relative to V1. (B) High magnification picture taken from the section in (A) reveals low contrast, regularly spaced CO blobs. These CO blobs are tightly packed together, often appearing connected or banded because the visual cortex is substantially smaller at this age. Scale bars: A, 5 mm; B, 1 mm.

Figure 5.

Aligned tangential sections (right) through layers 2/3 and into layer 4 show a clear pattern of CO blobs in a 2.5 week old kitten (K177). A subset of the radial blood vessels used to align the sections are indicated by the white arrowheads. The black arrows pointing to the Nissl stained coronal section (left) indicate the corresponding laminar location of the tangential sections. Notice that at this age lamination is not complete and there is still a zone of compact cells (() below layer 1. Scale bars: coronal Nissl section, 100 μm; tangential CO sections, 1 mm.

Figure 5.

Aligned tangential sections (right) through layers 2/3 and into layer 4 show a clear pattern of CO blobs in a 2.5 week old kitten (K177). A subset of the radial blood vessels used to align the sections are indicated by the white arrowheads. The black arrows pointing to the Nissl stained coronal section (left) indicate the corresponding laminar location of the tangential sections. Notice that at this age lamination is not complete and there is still a zone of compact cells (() below layer 1. Scale bars: coronal Nissl section, 100 μm; tangential CO sections, 1 mm.

Figure 6.

CO staining in kitten LGN (2.5 weeks of age, K177) exhibits dark staining intensity in both layers A and A1, while the C laminae are relatively lightly stained. Scale bar: 100 μm.

Figure 6.

CO staining in kitten LGN (2.5 weeks of age, K177) exhibits dark staining intensity in both layers A and A1, while the C laminae are relatively lightly stained. Scale bar: 100 μm.

Figure 7.

The six panels in this figure show the pattern of CO staining observed in young kittens at 2 weeks of age [(A) K176 and (B) K168], 2.5 weeks of age [(C) K171 and (D) K177] and 3 weeks of age [(E) K178 and (F) K175]. The blobs are first observed at 2 weeks of age and develop very rapidly thereafter. Scale bar: 1 mm.

Figure 7.

The six panels in this figure show the pattern of CO staining observed in young kittens at 2 weeks of age [(A) K176 and (B) K168], 2.5 weeks of age [(C) K171 and (D) K177] and 3 weeks of age [(E) K178 and (F) K175]. The blobs are first observed at 2 weeks of age and develop very rapidly thereafter. Scale bar: 1 mm.

Figure 8.

(A) A tangential section through the supragranular layers shows an obvious pattern of CO blobs throughout V1 of a 4 week old kitten (K167). Note that the CO staining lateral to V1 in V2 is non-uniform and darker than V1. (B) A higher magnification photomicrograph taken from the area centralis representation in (A) shows a regular pattern of CO blobs in V1 that appears very similar to the pattern observed in adults. Scale bars: A, 5 mm; B, 1 mm.

Figure 8.

(A) A tangential section through the supragranular layers shows an obvious pattern of CO blobs throughout V1 of a 4 week old kitten (K167). Note that the CO staining lateral to V1 in V2 is non-uniform and darker than V1. (B) A higher magnification photomicrograph taken from the area centralis representation in (A) shows a regular pattern of CO blobs in V1 that appears very similar to the pattern observed in adults. Scale bars: A, 5 mm; B, 1 mm.

Figure 9.

The pattern of CO blobs at 6 weeks of age is indistinguishable from the adult pattern. (A) A single tangential section through the supragranular layers of a 6 week old animal shows that blobs are found throughout V1 (K198). (B) At higher magnification the blobs are clearly defined darker patches of CO staining, some abut adjacent blobs while others are isolated blobs. Scale bars: A, 5 mm; B, 1 mm.

Figure 9.

The pattern of CO blobs at 6 weeks of age is indistinguishable from the adult pattern. (A) A single tangential section through the supragranular layers of a 6 week old animal shows that blobs are found throughout V1 (K198). (B) At higher magnification the blobs are clearly defined darker patches of CO staining, some abut adjacent blobs while others are isolated blobs. Scale bars: A, 5 mm; B, 1 mm.

Figure 10.

A non-uniform pattern of CO staining in V2 at 4 weeks of age (K167) is observed in tangential sections through layers 2/3 and layer 4. (A and B) The dark patches of CO staining in V2 are indicated by the arrows and the V2 patches are larger and darker than the blobs in V1 which are visible at the top of (A). Some V2 patches appear elongated, while others are more circular. Scale bar: 1 mm.

Figure 10.

A non-uniform pattern of CO staining in V2 at 4 weeks of age (K167) is observed in tangential sections through layers 2/3 and layer 4. (A and B) The dark patches of CO staining in V2 are indicated by the arrows and the V2 patches are larger and darker than the blobs in V1 which are visible at the top of (A). Some V2 patches appear elongated, while others are more circular. Scale bar: 1 mm.

Figure 11.

The pattern of CO staining in flattened sections through the supragranular layers of V1 in animals dark-reared from birth. Dark rearing to 4 weeks (A) (C792) or 6 weeks (C) (C802) of age has no obvious effect on the pattern of CO blobs in V1 compared with normal animals. (B and D) High magnification pictures taken from sections (A) and (C), respectively, reveal a regular pattern of darkly stained blobs in dark-reared kittens that have a contrast comparable with normal animals. Scale bars: A and C, 5 mm; B and D, 1 mm.

Figure 11.

The pattern of CO staining in flattened sections through the supragranular layers of V1 in animals dark-reared from birth. Dark rearing to 4 weeks (A) (C792) or 6 weeks (C) (C802) of age has no obvious effect on the pattern of CO blobs in V1 compared with normal animals. (B and D) High magnification pictures taken from sections (A) and (C), respectively, reveal a regular pattern of darkly stained blobs in dark-reared kittens that have a contrast comparable with normal animals. Scale bars: A and C, 5 mm; B and D, 1 mm.

Figure 12.

The pattern of CO staining in the superficial layers of V1 after monocular deprivation from eye opening into adulthood (K5255). (A) Regularly spaced CO blobs are easily visualized in V1 from monocularly deprived cats. (B) This high magnification view from the area centralis representation in (A) shows that many of the blobs exhibit staining intensities comparable with normal animals, however, qualitatively some blobs appear to be less intensely stained. Scale bars: A, 5 mm; B, 1 mm.

Figure 12.

The pattern of CO staining in the superficial layers of V1 after monocular deprivation from eye opening into adulthood (K5255). (A) Regularly spaced CO blobs are easily visualized in V1 from monocularly deprived cats. (B) This high magnification view from the area centralis representation in (A) shows that many of the blobs exhibit staining intensities comparable with normal animals, however, qualitatively some blobs appear to be less intensely stained. Scale bars: A, 5 mm; B, 1 mm.

Figure 13.

(A) CO blobs are apparent throughout the superficial layers of V1 after binocular deprivation to 6 weeks (K197). High contrast, regularly spaced CO blobs were obvious in V1 of all binocularly deprived animals. (B) A high magnification view from the area centralis representation in (A) shows that blobs in binocularly deprived cats appear very similar to those observed in normal animals. Scale bars: A, 5 mm; B, 1 mm.

Figure 13.

(A) CO blobs are apparent throughout the superficial layers of V1 after binocular deprivation to 6 weeks (K197). High contrast, regularly spaced CO blobs were obvious in V1 of all binocularly deprived animals. (B) A high magnification view from the area centralis representation in (A) shows that blobs in binocularly deprived cats appear very similar to those observed in normal animals. Scale bars: A, 5 mm; B, 1 mm.

Figure 14.

The blob-to-interblob contrast, expressed as a percentage of the mean adult contrast, is plotted as a function of age for normal (○), dark-reared (•), monocularly deprived (▴) and binocularly deprived (▪) hemispheres. Symbols that overlap are shifted slightly horizontally so that all of the data points are visible. The contrast values for normal hemispheres increases rapidly between 2 and 4 weeks of age and by 6 weeks of age has reached the mean adult contrast value. The development of blob-to-interblob contrast for the three deprivation conditions followed the same pattern as the normally reared animals. Visual experience is not necessary for the initial development of blob staining intensity.

Figure 14.

The blob-to-interblob contrast, expressed as a percentage of the mean adult contrast, is plotted as a function of age for normal (○), dark-reared (•), monocularly deprived (▴) and binocularly deprived (▪) hemispheres. Symbols that overlap are shifted slightly horizontally so that all of the data points are visible. The contrast values for normal hemispheres increases rapidly between 2 and 4 weeks of age and by 6 weeks of age has reached the mean adult contrast value. The development of blob-to-interblob contrast for the three deprivation conditions followed the same pattern as the normally reared animals. Visual experience is not necessary for the initial development of blob staining intensity.

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