12.4 BRAIN LACTATE IS RELATED TO COGNITION IN SCHIZOPHRENIA

Abstract Laura Rowland, University of Maryland School of Med: Bioenergetic function may be altered in schizophrenia as supported by post-mortem, preclinical, cerebrospinal fluid, and 31P-magnetic resonance spectroscopy (MRS) research. Impairments in bioenergetic function may lead to cognitive and functional dysfunction, characteristics of the illness. First, a 7T MRS study that tested the hypothesis that frontal lactate concentrations are elevated in schizophrenia and related to cognitive impairments will be presented. Second, recent advances in brain lactate measurements with 3T MRS will be presented. Methods Twenty-nine controls and 27 participants with schizophrenia completed the study. MRS scanning was conducted on a Philips ‘Achieva’ 7T scanner, and spectra were acquired from a frontal voxel using STEAM (TE/TM/TR=14/33/3000 ms, 128 NEX, 16 NEX water). Participants completed the MATRICS Consensus Cognitive Battery (MCCB) for cognitive function and UCSD Performance-Based Skills Assessment (UPSA) for functional capacity. The relationships between lactate, MCCB, and UPSA were examined. 3T MRS test-retest measures of lactate were conducted on a Siemens Prisma scanner using spectra editing (TE/TR=140/3, editing pulse at 4.1ppm with 30Hz bandwidth, 360 NEX, 16 NEX water). Results Patients had significantly higher lactate compared to controls (p = 0.045). Higher lactate was associated with poorer general cognitive function (r=-0.36, p=0.01) Visual learning, processing speed, and reasoning/problem solving cognitive domains showed the strongest relationships with lactate. Poorer functional capacity (r=-0.43, p=0.001) was also related to higher lactate. 3T spectral editing studies showed excellent reproducibility with a mean coefficient of variation of 4%. Discussion Higher frontal lactate levels in schizophrenia support the hypothesis that brain bioenergetics are altered and related to cognitive and functional impairments in schizophrenia. Higher lactate could be due to inefficient aerobic metabolism causing a shift towards anaerobic metabolism or poor utilization of lactate. Lactate measurements are doable at 3T field strength and may be a useful biomarker of cognition in schizophrenia. Interventions to promote efficient mitochondrial energy metabolism may prove useful for enhancing cognition and alleviating functional impairments in schizophrenia.

Background: System xc-is a plasma membrane amino acid antiporter, of mainly glial origin, that couples the import of cystine with the export of glutamate. System xc-(specific subunit xCT) contributes substantially to ambient extracellular glutamate levels in various regions of the brain, including the striatum and hippocampus. Despite the fact that system xc-is highly expressed in the brain and is a proposed therapeutic target for various neurological disorders, its function under physiological conditions in the central nervous system remains poorly understood. By acting as a source of glial extrasynaptic glutamate, system xc-might modulate synaptic transmission as a mechanism of neuro-glial communication. Previous electrophysiological findings indicate that system xc-delivered glutamate can inhibit excitatory synaptic neurotransmission in the corticoaccumbens pathway and at hippocampal CA3-CA1 synapses. To gain further insight into the proposed function of system xc-as modulator of synaptic transmission, we here focus on corticostriatal synapses.
Methods: Single section electron microscopy was carried out on VGLUT1pre-embed and glutamate immunogold post-embed labeled slices of the dorsolateral striatum of xCT+/+ and xCT-/-mice. Various parameters related to the pre-and post-synaptic compartments were integrated on the obtained electron micrographs, including glutamate immunogold density in the presynaptic terminal and spine, area of the terminal and spine, measures of the postsynaptic density (PSD) (length, area, thickness, and maximum thickness), percentage of PSDs showing perforations, and width of the synaptic cleft. Electrophysiological measures of corticostriatal transmission were obtained by recording the amplitude of field excitatory postsynaptic potentials (fEPSPs) after stimulation of corticostriatal fibers. Finally, grooming behavior was compared between xCT-/-and xCT+/+ littermates. Results: Genetic deletion of xCT led to depletion of glutamate immunogold labeling from corticostriatal terminals and their corresponding dendritic spines. Absence of xCT did not, however, affect the morphology of corticostriatal synapses, as evaluated by the area of the terminals and spines, size of the PSD, and width of the synaptic cleft. Similarly, no changes could be observed in the density of VGLUT1-positive synapses, indicating normal cortical innervation and spine density. Electrophysiological recordings revealed decreased amplitude of fEPSPs in xCT-/-mice after stimulation of corticostriatal fibers. Preliminary investigations revealed that this reduced response can be rescued by restoring physiological levels of glutamate to xCT-/-slices. Changes in corticostriatal transmission were not reflected in aberrant grooming behavior in xCT-/-mice; we could not observe any difference in the total grooming duration, the number of grooming bouts, the average bout duration or the latency to onset to grooming between xCT-/and xCT+/+ mice. Discussion: Contrary to available evidence at hippocampal and corticoaccumbens pathways, our findings indicate a positive effect of system xcon basal synaptic transmission at corticostriatal synapses. The decreased response we observed after stimulation of corticostriatal fibers in xCT-/mice was accompanied by depletion of glutamate immunogold labeling from corticostriatal terminals, suggesting a possible defect in presynaptic glutamate handling. Given the strong decrease (70%) in extracellular glutamate levels previously reported in this strain of mice, we hypothesize that the decreased presynaptic glutamate labeling in xCT-/-mice is related to a loss of extracellular glutamate needed to supply terminals for proper excitatory transmission. This hypothesis is supported by our preliminary results showing increased responses in xCT-/-slices after restoring physiological levels of glutamate. Together, our findings shed new light on the role of system xc-in controlling synaptic transmission, and suggest that it may play an important role in supplying presynaptic terminals with glutamate as an alternative mechanism to the glutamate-glutamine cycle. As a novel modulator of corticostriatal transmission, system xc-may be of interest as a possible therapeutic target for disorders with a corticostriatal component, such as schizophrenia or obsessive-compulsive disorder. Laura Rowland, University of Maryland School of Med: Bioenergetic function may be altered in schizophrenia as supported by post-mortem, preclinical, cerebrospinal fluid, and 31P-magnetic resonance spectroscopy (MRS) research. Impairments in bioenergetic function may lead to cognitive and functional dysfunction, characteristics of the illness. First, a 7T MRS study that tested the hypothesis that frontal lactate concentrations are elevated in schizophrenia and related to cognitive impairments will be presented. Second, recent advances in brain lactate measurements with 3T MRS will be presented.

BRAIN LACTATE IS RELATED TO
Methods: Twenty-nine controls and 27 participants with schizophrenia completed the study. MRS scanning was conducted on a Philips 'Achieva' 7T scanner, and spectra were acquired from a frontal voxel using STEAM (TE/TM/TR=14/33/3000 ms, 128 NEX, 16 NEX water). Participants completed the MATRICS Consensus Cognitive Battery (MCCB) for cognitive function and UCSD Performance-Based Skills Assessment (UPSA) for functional capacity. The relationships between lactate, MCCB, and UPSA were examined. 3T MRS test-retest measures of lactate were conducted on a Siemens Prisma scanner using spectra editing (TE/TR=140/3, editing pulse at 4.1ppm with 30Hz bandwidth, 360 NEX, 16 NEX water). Results: Patients had significantly higher lactate compared to controls (p = 0.045). Higher lactate was associated with poorer general cognitive function (r=-0.36, p=0.01) Visual learning, processing speed, and reasoning/problem solving cognitive domains showed the strongest relationships with lactate. Poorer functional capacity (r=-0.43, p=0.001) was also related to higher lactate. 3T spectral editing studies showed excellent reproducibility with a mean coefficient of variation of 4%. Discussion: Higher frontal lactate levels in schizophrenia support the hypothesis that brain bioenergetics are altered and related to cognitive and functional impairments in schizophrenia. Higher lactate could be due to inefficient aerobic metabolism causing a shift towards anaerobic metabolism or poor utilization of lactate. Lactate measurements are doable at 3T field strength and may be a useful biomarker of cognition in schizophrenia. Interventions to promote efficient mitochondrial energy metabolism may prove useful for enhancing cognition and alleviating functional impairments in schizophrenia.

Michael Bloomfield University College London
Overall Abstract: There are converging lines of evidence that the endocannabinoid system is involved in the pathophysiology of schizophrenia and that understanding these mechanisms may lead to novel treatment targets. In this symposium, we will present a series of experiments that link cannabinoid pharmacology to major fields of schizophrenia research including the dopaminergic, glutamatergic and serotonergic systems, glial cell function and the genetics of cognition. Dopamine is a major neurotransmitter implicated in the pathophysiology of schizophrenia. Thus, understanding processes that modulate dopaminergic signalling may lead to new insights into the biology and treatment of this disorder. The endocannabinoids anandamide and 2-arachidonoylglicerol (2-AG) modulate dopaminergic neural activity through interactions with CB1 and CB2 receptors. CB1 antagonists inhibit the effects of drugs that potentiate dopaminergic activity, such as cocaine. There is also evidence of interactions between CB1 and CB2 receptors in terms of cannabinoid-mediated changes in dopaminergic function. We will present new evidence that CB2 receptor antagonism opposes the inhibitory effects of rimonabant on cocaine-induced hyperlocomotion. Thus, highlighting the co-modulatory role of CB1 and CB2 receptors on dopaminergic function. We will then present a new study investigating the antipsychotic mode of action of cannabidiol (CBD). CBD attenuates the psychotomimetic effects of delta-9-tetrahydrocannabinol (THC) and there is evidence that CBD has antipsychotic effects in patients with psychosis. CBD prevents a range of behavioural impairments associated with the NMDA hypofunction model of psychosis measured in the pre-pulse inhibition, social interaction and novel object recognition tests following a two week exposure to the NMDA antagonist MK801. In addition, CBD, prevented neural (measured by delta-FosB) and microglia activation, and the decreased decrease in the number of medial prefrontal parvalbumin-positive neurons. The effects of CBD were blocked by pre-treatment with the 5-HT1A receptor antagonist WAY100635. This indicates that the antipsychotic effects of CBD may be mediated via 5HT1A-mediated mechanisms.
Next, we will describe the effects of CBD on glial cells. Glial cells, which express CB1 and CB2 receptors and synthesise endocannabinoid transmitters, have been implicated in schizophrenia whereby oligodendrocyte dysfunction has been associated with white matter deficits in the illness. In an investigation of the effects of CBD on a human oligodendrocyte culture (MO3.13), CBD administration resulted in diverse changes in the expression of proteins implicated in the pathophysiology of schizophrenia. Finally, we provide further evidence that polymorphisms in cannabinoid receptor genes are associated with cognitive impairments in humans. In particular, the rs12720071 polymorphism T/T allele is associated with impaired working memory in patients with psychosis.

ENDOCANNABINOID MODULATION OF DOPAMINE NEUROTRANSMISSION Fabricio Moreira* ,1 1 Federal University of Minas Gerais
Background: Dopamine is the major neurotransmitter implicated in schizophrenia pathology. Thus, understanding the processes modulating dopaminergic signalling may lead to new insights in the biology and treatment of this disorder. The endocannabinoids anandamide and 2-arachidonoylglicerol (2-AG) modulate neural activity through interactions CB1 and CB2 receptors. CB1 antagonists inhibit the effects of drugs that facilitate dopamine activity, such as cocaine. Similar to CB1 antagonists, CB2 agonists counteract the effects of cocaine in experimental animals. However, the functions of these receptors have been investigated separately. Here we test the hypothesis that CB1 and CB2 receptors interact to ameliorate the behavioural and molecular processes altered under hyperdopaminergic states. We also sought to identify the endocannabinoid involved in these effects. Methods: Male Swiss mice received cocaine injections to increase dopamine activity in the brain. The biological responses measured were hyperlocomotion, conditioned place preference, cFos expression and Erk protein phosphorylation in the nucleus accumbens. The animals received cannabinoid-related drugs before cocaine injections. The data were analysed with ANOVA followed by the Newman-Keuls test. Results: The CB1 receptor antagonist, rimonabant, and the CB2 receptor agonist, JWH133, inhibited cocaine-induced hyperlocomotion. Moreover, the CB2 antagonist, AM630, reversed the inhibitory effects of rimonabant in cocaine-induced hyperlocomotion, cFos expression, Erk phosphorylation and conditioned place preference. The inhibitors of anandamide and 2-AG hydrolysis, URB597 (FAAH inhibitor) and JZL184 (MGL inhibitor), respectively, were ineffective in inhibiting cocaine hyperlocomotion. However, when combined with a sub-effective dose of rimonabant, JZL184 (but not URB597), inhibited cocaine effects. Discussion: A CB2 antagonist reversed the effect of a CB1 antagonist, suggesting that these receptors modulate cocaine effects in opposite ways. Accordingly, increasing brain 2-AG levels inhibited cocaine effects only if CB1 is blocked and CB2 available. Thus, selective activation of CB2 receptors warrants further investigation as a new strategy for the treatment of psychiatric disorders resulting from hyperdopaminergic states.

CANNABIDIOL AS AN ANTIPSYCHOTIC DRUG
Francisco Guimaraes* ,1 , Naielly Rodrigues 1 , Nicole Silva 1 , Felipe Gomes 2 1 School of Medicine of Ribeirao Preto-University of Sao Paulo; 2 University of Pittsburgh Background: The phytocannabinoid cannabidiol (CBD) attenuates the psychotomimetic effects produced by high doses of delta-9-tetrahydrocannabinol (THC), the main component of the Cannabis sativa plant.