Spinal facilitation in cholinergic-sympathetic efferents by desipramine.

Electrodermal potentials (EDPs) evoked by electrical stimulation of the cholinergic-sympathetic system at different levels were recorded in the forepaws of anaesthetized cats and used as a measure of sudomotor activity. After pretreatment with yohimbine (0.25 mg/kg i.v.) to block alpha 2-adrenoceptors, unilateral electrical stimulation of the hypothalamus (square wave pulses 1 ms duration, 16 Hz, 2 s train length at intervals of 1 min) induced EDPs in both forepaws. Injection of the inhibitor of neuronal catecholamine reuptake, desipramine (1 mg/kg i.v.), facilitated the EDPs in both forepaws, even though access of the drug to the sweat glands was prevented by application of a tourniquet to one paw. The facilitation was abolished by injection of the specific alpha 1-adrenoceptor antagonist, prazosin (0.5 mg/kg i.v.). An equal enhancement of this effect by desipramine (1 mg/kg i.v.) and its abolition by prazosin (0.5 mg/kg i.v.) was obtained in cats with the brain stem transected at the level of the medulla oblongata and electrical stimulation of the spinal cord at C1. EDPs evoked in the right forepaw by preganglionic electrical stimulation of the right stellate ganglion were inhibited by desipramine (1 mg/kg i.v.). From these and previous results it is concluded that inhibition of neuronal reuptake of catecholamines results in facilitation of activity in sudomotor efferents. This effect is mediated by spinal alpha 1-adrenoceptors and provides an explanation of the occasional occurrence of excessive sweating in psychiatric patients treated with tricyclic antidepressants.