Interneuron circuits and brain oscillations in rat models of schizophrenia

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DESCRIPTION (provided by applicant): The recent shift in the conceptualization of schizophrenia from errors in dopamine neurotransmission to core deficits in information processing gave rise to a new generation of animal models focusing on the neurodevelopmental aspects and on the role of other systems, such as NMDA and GABA. Importantly, these models exhibit the animal equivalents of schizophrenia-related neurocognitive deficits and show characteristic abnormalities in the organization of the GABAergic interneuron networks, specifically in the hippocampus and prefrontal cortex, reminiscent of those in schizophrenic patients. GABAergic interneurons are involved in the generation of brain oscillations which in turn are known to be critical for cognitive processes. Their alterations in schizophrenic patients were proposed to significantly contribute to the neurocognitive impairments characteristic for this disease. The proposed project will examine the mechanisms of oscillatory synchronization in these models in an attempt of finding a link between the structural changes and neurocognitive deficits. We hypothesize that pathologic alterations in the neuronal circuitry in chronic neurodevelopmental animal models of schizophrenia will result in impaired oscillatory synchronization in the hippocampus and prefrontal cortex which in turn contribute to the neurocognitive deficits. We will test the specific hypothesis that this impairment correlates with the extent of damage to the local GABAergic interneuron network and in particular with the loss of parvalbumin positive basket and chandelier cells. Neuronal synchronization in the hippocampus and prefrontal cortex will be tested in two animal models each exhibiting abnormalities reminiscent of the neurocognitive deficits of human schizophrenia and each showing involvement of GABAergic mechanisms and a reduction of parvalbumin positive interneurons. The two models represent chronic conditions but are produced by different interventions; one is a neurodevelopmental model, the other is drug-induced in adult rats and is based on systemic NMDA antagonism. Electrophysiological signals will be processed for detection and analysis of their rhythmic components (power spectra, phase, and coherence). The brains will be processed for immunohistological examination of the hippocampus, prefrontal cortex, and medial septum and the results of electrophysiology will be compared with the extent of the reduction in parvalbumin expressing interneurons. This work will increase our neuronal level understanding of the mechanisms of cognitive deficits in schizophrenia and may lead to new strategies for drug development. PUBLIC HEALTH RELEVANCE: Contemporary views of schizophrenia regard cognitive dysfunction as the primary core deficit due to dysfunction of neuronal microcircuits. Brain oscillations are known to be critical for cognitive processes and their alterations in schizophrenic patients were proposed to significantly contribute to the neurocognitive impairments characteristic for this disease. This project will examine the functioning of neuronal networks involved in cortical oscillations in neurodevelopmental animal models of schizophrenia in an attempt of finding a link between the structural changes and neurocognitive deficits and will thus increase our neuronal level understanding of the mechanisms of cognitive deficits in schizophrenia and will facilitate the development of new strategies for drug development.