Antidepressant drug action and presynaptic alpha-receptors

Receptors have been demonstrated on the terminations of the sympathetic adrenergic nerves. One type, the so-called alpha 2-receptors, are activated by the norepinephrine that is released from the nerve terminals into the synaptic cleft; this activation causes a reduction in the output of the transmitter (negative feedback). Recent studies have demonstrated that certain antidepressant drugs can block these alpha 2-receptors and thus prevent their inhibitory action on the release of norepinephrine. If this occurs in the brain, the increases in norepinephrine levels could help explain the antidepressant action of these agents.