Preferential reduction of binding of 125I-iodopindolol to beta-1 adrenoceptors in the amygdala of rat after antidepressant treatments

This study utilized quantitative receptor autoradiography to examine the effects of repeated administration of antidepressants to rats on the binding of the beta adrenoceptor antagonist, 125I-iodopindolol (125I-IPIN) to either beta-1 or beta-2 adrenoceptors in various regions of brain. Antidepressants were selected to represent various chemical and pharmacological classes including tricyclic compounds (desipramine and protriptyline), monoamine oxidase inhibitors (clorgyline, phenelzine and tranylcypromine), atypical antidepressants (mianserin and trazodone) and selective inhibitors of the uptake of serotonin (citalopram and sertraline). Additionally, rats were treated with various psychotropic drugs that lack antidepressant efficacy (cocaine, deprenyl, diazepam and haloperidol). Repeated treatment of rats with desipramine, protriptyline, clorgyline, phenelzine, tranylcypromine or mianserin reduced the binding of 125I-IPIN to beta-1 adrenoceptors in many brain areas. Only in the basolateral and lateral nuclei of the amygdala did all six of these antidepressants significantly reduce 125I-IPIN binding to beta-1 adrenoceptors. In these amygdaloid nuclei, the magnitude of the reduction in the binding of 125I-IPIN caused by each of these drugs was comparable to or greater than the reduction in binding produced in any other region of brain. Reductions of binding of 125I-IPIN after antidepressant treatments were not consistently observed in the cortex, the area of brain examined most often in homogenate binding studies. Only the monoamine oxidase inhibitors caused reductions in the binding of 125I-IPIN to beta-2 adrenoceptors, and this effect was generally localized to the amygdala and hypothalamus. Repeated treatment of rats with citalopram, sertraline, or trazodone or with drugs lacking clinical antidepressant efficacy caused no significant effects on the binding of 125I-IPIN to either subtype of beta adrenoceptor in any region of brain. These results demonstrate that amygdaloid beta-1 adrenoceptors are particularly susceptible to regulation by certain antidepressant treatments and implicate the amygdala as an important site of action for antidepressants with pharmacological activity on noradrenergic neurons.