The central hypothesis of this Center posits that a distinctive pattern of molecular alterations in subsets of GABA neurons gives rise to disturbances in cortical network oscillations that underlie the information processing deficits of schizophrenia. Disturbances in markers of cortical GABA neurotransmission are common in schizophrenia and are most prominent in two types of GABA neurons: parvalbumin-positive (PV), fast-spiking neurons and somatostatin-positive (SST), low-threshold spiking neurons. PV and SST cells each form networks with neurons of the same type that are thought to play central roles in the generation of gamma (30-80 Hz) and theta (4-7 Hz) oscillations, respectively, both of which are disturbed in subjects with schizophrenia. Network oscillations depend, at least in part, on 3 physiological properties: 1) the strength [i.e., inhibitory post-synaptic current (IPSC) amplitude] of GABA neurotransmission as determined by both pre- and post-synaptic factors;2) the kinetics (i.e., IPSC duration) of GABA neurotransmission as determined principally by the subunit composition of post-synaptic GABA-A receptors;and 3) the nature of the resulting inhibition (i.e., shunting or hyperpolarizing) as determined by chloride ion flow when GABA-A receptors are activated. Each of these physiological features is, in turn, dependent upon the expression of particular sets of gene products. Consequently, we hypothesize that the alterations in gamma and theta oscillations in schizophrenia reflect cell type-specific disturbances in the gene products that influence the strength, kinetics or nature of GABA-mediated inhibition. Studies in postmortem human brain, using the dorsolateral prefrontal cortex (DLPFC) as a prototypic cortical region affected in schizophrenia, will be conducted to determine if 1) the presynaptic strength of GABA neurotransmission in schizophrenia is impaired due to deficits in the amount of GAD67 protein available to synthesize GABA in PV and SST neurons;2) if cell type-specific alterations in the expression of a1 and a2 GABA-A receptor subunits disrupt the kinetics of GABA neurotransmission in schizophrenia;and 3) if shifts in the expression of chloride transporters in schizophrenia disrupt the shunting inhibitory input to GABA neurons and/or the hyperpolarizing inhibitory input to pyramidal cells required for robust oscillations. The proposed studies are both methodologically and conceptually innovative, and these investigations depend upon and inform the studies proposed in other projects in this Center. Thus, the outcomes of the proposed studies are likely to be highly informative regarding both the disease mechanisms underlying oscillatory and information processing deficits in schizophrenia and in identifying novel molecular targets for treating these deficits.
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