Functional supersensitivity of CNS alpha 1-adrenoceptors following chronic antidepressant treatment

Chronic but not acute administration (21 days) of desipramine (10 mg/kg), amitriptyline (10 mg/kg) or iprindole (5 mg/kg) enhanced the stimulatory effect of the alpha 1-adrenergic agonist phenylephrine on the acoustic startle reflex when phenylephrine was infused into the subarachnoid space of the spinal cord. Comparable supersensitivity to phenylephrine also occurred 1 week after selective depletion of norepinephrine in the spinal cord via intrathecal administration of 6-hydroxydopamine. Behavioral supersensitivity to phenylephrine was associated with an increase in the number of 3H-prazosin binding sites following denervation but not following chronic antidepressant treatments. The results indicate that chronic antidepressant treatments may enhance functional alpha 1-adrenergic transmission through mechanisms different than those following denervation.