Chronic antidepressant treatment enhances agonist affinity of brain alpha 1-adrenoceptors

Binding of [3H]prazosin, a selective alpha 1-adrenoceptor antagonist, to thalamic membranes was studied following chronic treatment of rats with tricyclic antidepressants. Rosenthal analysis showed no change in the number or affinity of antagonist binding sites; however, the ability of the alpha 1-agonist phenylephrine to compete for these sites was significantly enhanced after chronic tricyclic treatment. This result is consistent with previous studies showing physiological alpha 1-supersensitivity in thalamus after chronic antidepressant administration.