Cyclic AMP in the rat cerebral cortex after stimulation of the locus coeruleus: decrease by antidepressant drugs.

The study concerned the effect of repeated treatment with antidepressant drugs on the elevation of cyclic AMP levels in the rat cerebral cortex following electrical stimulation of the locus coeruleus. Some of the tricyclic and tetracyclic antidepressant drugs inhibited the cyclic AMP response. Desmethylimipramine was the most potent (effective when given 5 mg/kg/day for 2 weeks). Imipramine and nomifensine (daily dose 10 mg/kg for 2 weeks) produced slight decreases, while iprindol and clomipramine were ineffective. After 6 weeks of treatment (daily 10 mg/kg) iprindol, clomipramine and mianserin were without effect. The cyclic AMP response was suppressed by higher doses of the latter two drugs (2 weeks, 20 mg/kg/day). These results indicate that tricyclic and tetracyclic antidepressant drugs are able to decrease cerebral noradrenergic neurotransmission of locus coeruleus neurons, as far as this is mediated by cyclic AMP. It is not clear, however, whether such modification is related to the therapeutic action of antidepressant drugs.