Effects of chronic antidepressant treatment on beta-adrenoceptor subtype binding in the rat cerebral cortex and cerebellum.

The effects of desipramine, tranylcypromine, and phenelzine on beta-adrenoceptor subtype binding were measured in rat cerebral cortex and cerebellum. The drugs were administered to male Sprague Dawley rats for 28 d sc via 2ML4 Alzet osmotic minipumps (desipramine HCl 10, tranylcypromine HCl 1, phenelzine sulfate 5, 10 mg kg-1/d). Binding of [3H]CGP 12177 was measured to determine total beta-adrenoceptor density in each brain region. The relative densities of beta 1- and beta 2-adrenoceptors were directly calculated from competition analysis using ICI 89406 to displace [3H]CGP 12177. beta 1-Adrenoceptor density was decreased in cortical tissue following each antidepressant treatment, but no effects on beta 2-adrenoceptor density were evident. With cerebellar tissue, despite a higher density of beta 2-adrenoceptors in this area, no effects of antidepressants on beta 2-adrenoceptor density were evident. The present data confirm and extend previous reports of beta 1- but not beta 2-adrenoceptor downregulation in brain following chronic antidepressant drug treatment.