DEXMEDETOMIDINE REDUCES RESPONSE TENDENCY, BUT NOT ACCURACY OF RATS IN ATTENTION AND SHORT-TERM-MEMORY TASKS

The present study investigated the role of alpha(2)-adrenergic mechani sms in the performance of motor responses, attention and short-term me mory in rats. A low dose (3.0 mu g/kg, s.c.) of dexmedetomidine, an al pha(2)-adrenoceptor agonist, reduced response tendency in an attention al task and a working memory task, but it did not affect the choice ac curacy of rats. Atipamezole (300 mu g/kg), an alpha(2)-adrenoceptor an tagonist, increased anticipatory responding. Although atipamezole did not affect the number of omissions, it reversed the effects of dexmede tomidine on that parameter. We also investigated the effects of dexmed etomidine in rats with partial destruction of noradrenergic nerves ind uced by the neurotoxin DSP-4 (N(2-chloroethyl)-N-ethyl-2-bromobenzylam ine hydrochloride). On its own, DSP-4 treatment did not affect choice accuracy or behavioural activity of rats in the attentional task. The effects of dexmedetomidine (0.3-3.0 mu g/kg) on anticipatory responses did not differ between controls and DSP-4 group. Furthermore, the eff ect on omissions was not consistently diminished in DSP-4 treated rats . These results suggest that the activation of postsynaptic alpha(2)-a drenoreceptors may be responsible for dexmedetomidine-induced reductio n of response tendency while attention and short-term memory are not m arkedly affected. Copyright (C) 1997 Elsevier Science Inc.