Hippocampal α7 nicotinic acetylcholine receptor levels in patients with schizophrenia, bipolar disorder, or major depressive disorder

Background: The alpha 7 nicotinic acetylcholine receptor ( nAChR) is involved in cognitive function and synaptic plasticity. Consequently, changes in a7 nAChR function have been implicated in a variety of mental disorders, especially schizophrenia. However, there is little knowledge regarding the levels of the a7 nAChR in patients with bipolar disorder. Methods: We performed [125 I]-bungarotoxin autoradiography to selectively visualize and measure a7 nAChRs on postmortem sections of the temporal lobe from patients with schizophrenia, bipolar disorder, or major depressive disorder, as well as control subjects. Radioligand binding was determined in the dentate gyrus, CA3, and CA1 subfields of the hippocampus and the perirhinal cortex. Results: Bungarotoxin binding was significantly increased in the CA1 and perirhinal cortex of patients with bipolar disorder compared to control subjects, whereas in patients with schizophrenia or major depressive disorder the level of binding did not significantly differ from control subjects in any region measured. Conclusions: These data are consistent with the reported genetic associations linking the a7 nAChR to the pathology of bipolar disorder, and may suggest a dysfunction of a7 nAChR-dependent signalling in bipolar disorder. We could not reproduce the previously reported decrease in hippocampal bungarotoxin binding in schizophrenia.