EFFECT OF CLONIDINE ON THE HUMAN ACOUSTIC STARTLE REFLEX

The present study investigated in healthy human volunteers whether clo nidine reduced the amplitude of the acoustic startle reflex and whethe r this effect, if found, was due to an accelerated rate of habituation . Subjects were presented with startle-eliciting noise-bursts after in travenous (iv) infusion of clonidine (1.5 mu g/kg) and saline on separ ate days. Clonidine significantly reduced the amplitude of the acousti c startle reflex (as indexed by the eyeblink component) relative to th e saline treated condition. This effect was neither due to an accelera ted rate of habituation of the startle reflex nor to the sedative effe ct of clonidine. These findings complement an earlier report (Morgan e t al. 1993) that yohimbine augments the amplitude of the startle refle x in man. Taken together, the two reports indicate a new model for the clinical investigation of central alpha(2) adrenoceptor function in h umans.