The actions of epinephrine, an adrenal hormone and central neurotransmitter, and norepinephrine, a peripheral sympathetic and central neurotransmitter, are mediated through alpha-1, alpha-2, and beta-adrenergic receptors. In addition, a variety of drugs also produce their effects by interacting with these receptors. alpha-2 Adrenergic agonists, such as Clonidine and guanabenz, are widely used to treat hypertension. Clonidine is also used to ameliorate the symptoms of withdrawal from opiate drugs. Local administration of Clonidine has been used successfully in the treatment of glaucoma. Mianserin, an effective antidepressant drug, is an alpha-2 adrenergic antagonist. The utility of other alpha-2 adrenergic antagonists as antidepressant medications is currently a subject of intense study. Recently alpha-2 adrenergic agonists have been demonstrated to ameliorate the cognitive defects exhibited by aged nonhuman primates, and it has been suggested that these drugs may be helpful for patients with Alzheimer’s disease (Arnsten and Goldman-Rakic, 1985).