The intrinsic, horizontally projecting neurons in visual cortex are organized into discrete clusters, or patches. While earlier studies focused on the organization of the patches and their relationship to functional properties, such as orientation tuning and binocularity, little is known about the detailed morphology of the neurons in these patches. We retrogradely labeled patches of local, intracortical neurons (local patch neurons) by in vivo injections of fluorescent dextrans into area 18, then ion tophoresed Lucifer yellow into prelabeled cells in lightly fixed cortical slices, and examined the dendritic morphology of local patch neurons in layer 2/3 of area 18 by confocal laser scanning microscopy. Most of the neurons we examined were spiny pyramidal neurons, including modified pyramids, small to moderately large standard pyramids, and star pyramids. Smooth, multipolar cells of the basket and bipolar cell types were also present. The basal dendritic trees of more than 60% of the local patch pyramidal neurons in layer 2/3 displayed mediolaterally elongated dendritic fields. This finding appears to be specific for pyramidal neurons, as our sample of smooth, multipolar neurons did not show this trend.

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