The changes in noradrenergic and adrenergic activity that regulate beta-adrenergic receptors in the CNS have been assessed by lesion studies as well as by pharmacologic enhancement and inhibition of transmission. Beta-adrenergic receptor subtypes are differentially distributed throughout the CNS and are probably differentially regulated. An effect of normal aging on beta receptors has been found in studies of both animal and human brain tissue. Preliminary studies relating to neuropsychiatric disorders in humans and animal studies on the action of antidepressants suggest that CNS beta receptors may play a critical role in affective disorders and their treatment. This may explain why beta-blocker medication is associated with side effects such as depression and lethargy, which are generally reversible when selective hydrophilic beta blockers are used or when the therapy is withdrawn.