N-Methyl-d-Aspartic Acid Receptor Expression in the Dorsolateral Prefrontal Cortex of Elderly Patients With Schizophrenia

OBJECTIVE: The N-methyl-d-aspartic acid (NMDA) class of glutamate receptors has received attention in the pathophysiology of schizophrenia because of the similarity between some schizophrenic symptoms and symptoms caused by NMDA antagonists. To determine if NMDA receptor abnormalities were present at the mRNA level, expression of NMDA receptor (NR) subunits NR₁, NR_2A, and NR_2B was measured in specimens from the dorsolateral prefrontal cortex and the occipital cortex of elderly patients with schizophrenia and normal elderly subjects. METHOD: Postmortem specimens from antemortem assessed and diagnosed elderly patients with schizophrenia (N=26) were compared with those from a neuropathologically and neuropsychiatrically normal elderly comparison group (N=13) and from patients with Alzheimer’s disease (N=10). The mRNA expression of the NR₁, NR_2A, and NR_2B subunits and of postsynaptic density 95 (PSD-95), a protein associated with postsynaptic NMDA receptors, was studied with quantitative real-time reverse transcriptase polymerase chain reaction. RESULTS: Expression of NR₁ and NR_2A but not NR_2B subunits was higher in the dorsolateral prefrontal cortex and the occipital cortex of patients with schizophrenia than in the normal and Alzheimer’s disease groups. In contrast, NR₁ expression was significantly lower in the Alzheimer’s disease group. Occipital cortex expression of PSD-95 was higher in the schizophrenic subjects and correlated strongly with the expression of NR_2A and NR_2B in both cortical regions and with expression of NR₁ in the occipital cortex. These results were not influenced by neuroleptic exposure history, postmortem interval, or age of the subject. CONCLUSIONS: NMDA receptor subunits are abnormally expressed in elderly patients with schizophrenia. The disproportionate expression of the NR₁ and NR_2A subunits relative to NR_2B expression may have implications for the pathophysiology of schizophrenia and the sensitivity of schizophrenic patients to glutamate and glutamatergic drugs.