Platelet radioligand binding and neuroendocrine challenge tests in depression

Clonidine challenge testing of alpha-2-adrenoceptor function in man: the effects of mental illness and psychotropic medication

The clonidine challenge test is a means of assessing alpha-2-adrenoceptor sen sitivity in man. We review studies which have used this test to investigate central alpha-2- adrenoceptor changes in psychiatric illness, and to determine receptor changes after adminis tration and withdrawal of psychotropic treatments. Patients with severe depression show evidence of reduced alpha-2-adrenoceptor sensitivity, especially a reduced growth hormone response to clonidine. This may delineate a subgroup of patients with severe depressive illness from those with milder depression, and may even provide a trait marker for some depressed patients. Patients with panic disorder show evidence of subsensitivity to some and supersensitivity to other clonidine-induced responses. Other disorders, although less well investigated, may have abnormal test responses which may provide additional information about their cause and treatment. Changes in response after drug treatment have provided important information on the mode of action of antidepressants, and have suggested that noradrenergic function is altered by a variety of different antidepressants.

Rhythm and blues. Neurochemical, neuropharmacological and neuropsychological implications of a hypothesis of circadian rhythm dysfunction in the affective disorders

Current views on the organisation and functions of the circadian rhythm system are outlined. Evidence is presented supportive of the notion that the pathophysiology of the affective disorders involves a disruption of circadian rhythms and that the primary locus of action of agents effective in the affective disorders is on the circadian rhythm system. Potential disruptions of this system are enumerated. Such a hypothesis, it is argued, might potentially unite the disparate neurochemical and neuroendocrinological findings emerging in both depression and mania. There are in addition neuropsychological and nosological implications of such a framework, which may help bridge the divide between molecular and behavioural approaches to research on the affective disorders which are outlined.