To test the hypothesis that muscarinic receptors are involved in the pathology of schizophrenia, we measured muscarinic 1 (M1R) and muscarinic 4 (M4R) protein and mRNA as well as [ 3 H]pirenzepine binding in Brodmann's areas (BA) 9 and 40 obtained postmortem from 20 schizophrenic and 20 age/sex-matched control subjects. There was a significant decrease in [ 3 H]pirenzepine binding to BA 9 (mean ± SEM: 151 ± 15 vs 195 ± 10 fmol mg −1 ETE; P Ͻ 0.02), but not BA 40 (143 ± 13 vs 166 ± 11 fmol mg −1 ETE), from subjects with schizophrenia. The level of M1R protein (0.11 ± 0.007 vs 0.15 ± 0.008 OD; P Ͻ 0.01), but not M4R protein, was decreased in BA9 from schizophrenic subjects with neither receptor protein being altered in BA 40. The level of M1R mRNA was decreased in BA 9 (30 ± 7.0 vs 79 ± 14 dpm × 10 3 mg −1 ETE, P Ͻ 0.01) and BA 40 (28 ± 5.9 vs 99 ± 14, P Ͻ 0.01) with schizophrenia but M4R mRNA was only decreased in BA 40 (48 ± 6.6 vs 89 ± 9.9, P Ͻ 0.005). These data suggest that the M1R, at least in the dorsolateral prefrontal cortex, may have a role in the pathology of schizophrenia.

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The present study has identified genes that are differentially expressed in BA 46 in schizophrenia. Initial studies have shown that there is a need for a careful validation of genes shown to be affected in schizophrenia using high-throughput technologies. In addition the present study has shown that gene expression may vary considerably depending on the duration of schizophrenia. This raises the hypothesis that changing gene expression may be underlying the change in symptom profile that occurs with disease progression in some subjects with schizophrenia.

Changes in SNAP-25 and synaptophysin in BPDI suggest that changes in specific neuronal functions could be linked to the pathology of the disorder.

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