BA-024

Alcohol increases inhibitory neurotransmission, an effect mediated through GABA receptors. With chronic alcohol exposure, the inhibitory effects diminish. Glutamic acid decarboxylase (GAD) catalyzes glutamate in the synthesis of GABA. We sought to determine the amount of GAD_65/67 mRNA in anterior cingulate cortex (BA24) and orbital prefrontal cortex (BA45) of medication-free alcoholics and nonpsychiatric controls postmortem. Studies were performed in 16 pairs of nonpsychiatric controls and alcoholics, matched for age, sex and PMI. DSM-IV diagnosis of alcohol use disorder (AUD) was made by the SCID I in a psychological autopsy. Frozen blocks of BA24 or BA45 were sectioned (10 µm) for in situ hybridization of ³⁵S-labelled riboprobe for GAD_65/67 mRNA and autoradiograms were analyzed by quantitative densitometry. Three isodensity bands of labeling were evident, with different relative amounts of GAD₆₅ and GAD₆₇ (outer and inner, predominantly GAD₆₅, intermediate predominantly GAD₆₇), and the isodensity bands were analyzed separately. GAD_65/67 mRNA levels were not different between alcoholics and controls in the gray matter of BA24 (p = 0.53) or BA45 (p = 0.84) or in any of the three isodensity bands in which the GAD_65/67 mRNA was distributed. GAD_65/67 mRNA in white matter underlying either region was also not different in alcoholics (p > 0.05). GAD_65/67 mRNA levels did not correlate with age, sex or duration of alcoholism in either BA24 or BA45. Effects on inhibitory neurotransmission in alcoholics do not appear to be associated with change in the levels of GAD₆₅ or GAD₆₇ mRNA.

Increasingly, data are implicating muscarinic receptors in the aetiology and treatment of mood disorders. This led us to measure levels of different muscarinic receptor-related parameters in the cortex from people with mood disorders and the CNS of rats treated with mood stabilisers and antidepressant drugs.

We measured [(3)H]AF-DX 384 binding in BA 46 and BA 24 from subjects with bipolar disorders (n = 14), major depressive disorders (n = 19), as well as age- and sex-matched controls (n = 19) and the CNS of rats treated with fluoxetine or imipramine. In addition, we used Western blots to measure levels of CHRM2 protein and oxotremorine-M stimulated [(35)S]GTPγS binding as a measure of CHRM 2 / 4 signaling.

Compared with controls, [(3)H]AF-DX 384 binding was lower in BA 24 and BA 46 in bipolar disorders and major depressive disorders, while CHRM2 protein and oxotremorine-M stimulated [(35)S]GTPγS binding was only lower in BA 24. Compared with vehicle, treatment with mood stabilisers, antidepressant drugs for 10 days, or imipramine for 28 days resulted in higher levels of in [(3)H]AF-DX 384 binding select regions of rat CNS.

Our data suggest that levels of CHRM2 are lower in BA 24 from subjects with mood disorders, and it is possible that signalling by that receptor is also less in this cortical region. Our data also suggest increasing levels of CHRM2 may be involved in the mechanisms of action of mood stabilisers and tricyclic antidepressants.