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J Neurophysiol 100: 959-965, 2008. First published June 4, 2008; doi:10.1152/jn.00079.2008
0022-3077/08 $8.00
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Prolonged Exposure to NMDAR Antagonist Suppresses Inhibitory Synaptic Transmission in Prefrontal Cortex

Yuchun Zhang1, M. Margarita Behrens2 and John E. Lisman1

1Department of Biology and Volen Center for Complex Systems, Brandeis University, Waltham, Massachusetts; and 2Division of Geriatrics, Department of Medicine, University of California at San Diego, La Jolla, California

Submitted 23 January 2008; accepted in final form 30 May 2008

Postmortem studies have shown that schizophrenia produces a reduction in the 67-kilodalton isoform of glutamic acid decarboxylase (GAD67), a key enzyme for {gamma}-aminobutyric acid (GABA) synthesis. N-methyl-D-aspartate receptor (NMDAR) antagonists have been extensively used to study schizophrenia because they can induce many aspects of the disease, including the decrease in GAD67. It is generally thought that this reduction in GAD implies a reduction in functional inhibition, but direct evidence had been lacking. We have therefore performed physiological studies in slices of prefrontal cortex taken from rats treated with the NMDAR antagonist ketamine. Both frequency and amplitude of miniature inhibitory postsynaptic currents were reduced. Consistent with a reduction of inhibition, we observed an increase in postsynaptic excitability. The increased excitability is likely to result from disinhibition because miniature excitatory postsynaptic current properties and intrinsic excitability were not changed. Ketamine did not affect inhibition or GAD levels in young rats, indicating a developmental regulation that may be related to the developmental increase in ketamine sensitivity that occurs in humans. Our results show that NMDAR antagonist produces biochemical changes in the GABA system that lead to a functional disinhibition. Such disinhibition would be expected to decrease gamma oscillations, which are reduced in schizophrenia.

Address for reprint requests and other correspondence: J. E. Lisman, Department of Biology and Volen Center for Complex Systems, Brandeis University, MS 008, 415 South Street, Waltham, MA 02454 (E-mail: lisman{at}brandeis.edu)




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Interleukin-6 Mediates the Increase in NADPH-Oxidase in the Ketamine Model of Schizophrenia
J. Neurosci., December 17, 2008; 28(51): 13957 - 13966.
[Abstract] [Full Text] [PDF]


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