Pathological Basis for Deficient Excitatory Drive to Cortical Parvalbumin Interneurons in Schizophrenia

OBJECTIVE: Deficient excitatory drive to parvalbumin-containing cortical interneurons is proposed as a key neural substrate for altered gamma oscillations and cognitive dysfunction in schizophrenia. However, a pathological entity producing such a deficit has not been identified. The authors tested the hypothesis that cortical parvalbumin interneurons receive fewer excitatory synaptic inputs in individuals with schizophrenia. METHOD: Fluorescent immunohistochemistry, confocal microscopy, and post-image processing techniques were used to quantify the number of putative excitatory synapses (i.e., the overlap of vesicular glutamate transporter 1-positive VGlut1+ puncta and postsynaptic density protein 95-positive PSD95+ puncta) per surface area of parvalbumin-positive (PV+) or calretinin-positive (CR+) neurons in the dorsolateral prefrontal cortex from schizophrenia subjects and matched unaffected comparison subjects. RESULTS: Mean density of VGlut1+/PSD95+ puncta on PV+ neurons was 18% lower in schizophrenia, a significant difference. This deficit was not influenced by methodological confounds or schizophrenia-associated comorbid factors, not present in monkeys chronically exposed to antipsychotic medications, and not present in CR+ neurons. Mean density of VGlut1+/PSD95+ puncta on PV+ neurons predicted the activity-dependent expression levels of parvalbumin and glutamic acid decarboxylase 67 (GAD67) in schizophrenia subjects but not comparison subjects. CONCLUSIONS: To the authors' knowledge, this is the first demonstration that excitatory synapse density is lower selectively on parvalbumin interneurons in schizophrenia and predicts the activity-dependent down-regulation of parvalbumin and GAD67. Because the activity of parvalbumin interneurons is required for generation of cortical gamma oscillations and working memory function, these findings reveal a novel pathological substrate for cortical dysfunction and cognitive deficits in schizophrenia.