Effect of clonidine and chlorpromazine on centrally evoked electrodermal responses and their interaction with yohimbine

Both clonidine and chlorpromazine reduced the amplitude of electrodermal responses (EDR) evoked by stimulation of the hypothalamus at a constant submaximal frequency (10–16 Hz). The ED₅₀ for clonidine was approximately 5 μg/kg and that for chlorpromazine was about 1 mg/kg. Yohimbine pretreatment (0.5 mg/kg, i.v.) antagonized the effects of clonidine but did not alter the effectiveness of clorpromazine in inhibiting these responses. Yohimbine alone was without effect on these sympathetic-cholinergic responses. These results suggest that clonidine and chlorpromazine depress central sympathetic reactivity by different mechanisms.