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Original Article
July 7, 2008

Reduced Cortical Cannabinoid 1 Receptor Messenger RNA and Protein Expression in Schizophrenia

Author Affiliations

Author Affiliations: Departments of Psychiatry (Drs Eggan, Hashimoto, and Lewis) and Neuroscience (Dr Lewis), University of Pittsburgh, Pittsburgh, Pennsylvania.

Arch Gen Psychiatry. 2008;65(7):772-784. doi:10.1001/archpsyc.65.7.772
Abstract

Context  Cannabis use is associated with both impaired cognitive functions, including working memory, and an increased risk of schizophrenia. Schizophrenia is characterized by impairments in working memory that are associated with reduced γ-aminobutyric acid (GABA) neurotransmission in the dorsolateral prefrontal cortex. The cannabinoid 1 receptor (CB1R) is highly expressed in the dorsolateral prefrontal cortex, is contained in the axon terminals of a subpopulation of perisomatic-targeting GABA neurons, and, when activated, suppresses the release of GABA.

Objective  To determine the potential relationship between CB1R signaling and altered GABA neurotransmission in schizophrenia by evaluating CB1R messenger RNA (mRNA) and protein expression in the dorsolateral prefrontal cortex.

Design  In situ hybridization and immunocytochemistry techniques were used to examine the cortical levels of CB1R mRNA and protein, respectively.

Setting  Brain specimens were obtained from autopsies conducted at the Allegheny County Medical Examiner's Office, Pittsburgh, Pennsylvania.

Participants  Postmortem brain specimens from 23 pairs of subjects with schizophrenia and age-, sex-, and postmortem interval–matched comparison subjects, as well as brain specimens from 18 macaque monkeys with long-term exposure to haloperidol, olanzapine, or placebo.

Main Outcome Measures  Optical density measures of CB1R mRNA expression and protein levels and correlations with previously reported glutamic acid decarboxylase 67 and cholecystokinin mRNA measures.

Results  Levels of CB1R mRNA were significantly lower by 14.8% in the subjects with schizophrenia. Similarly, CB1R protein levels, assessed by radioimmunocytochemistry and standard immunocytochemistry, were significantly decreased by 11.6% and 13.9%, respectively. Group differences in CB1R mRNA levels were significantly correlated with those in glutamic acid decarboxylase 67 and cholecystokinin mRNA levels. Expression of CB1R mRNA was not changed in antipsychotic-exposed monkeys, and neither CB1R mRNA levels nor protein levels were affected by potential confounding factors in the subjects with schizophrenia.

Conclusions  This combination of findings suggests the testable hypothesis that reduced CB1R mRNA and protein levels in schizophrenia represent a compensatory mechanism to increase GABA transmission from perisomatic-targeting cholecystokinin interneurons with impaired GABA synthesis.

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