Using in vivo microdialysis infusion, we have studied the adrenoceptor subtypes implicated in paradoxical sleep (PS) generation in the cat. Both epinephrine and norepinephrine inhibited PS and induced PS without atonia when applied to the caudal peri-locus coeruleus-alpha (peri-LC alpha) of the mediodorsal pontine tegmentum. This effect was mimicked by clonidine, an alpha2-selective adrenoceptor agonist, while alpha1 and beta agonists were ineffective. The norepinephrine effect was antagonized by co-application of the alpha2-selective antagonists, rauwolscine or RX 821002, but not by alpha1 or beta1 antagonists. In addition, clonidine completely blocked the PS-inducing effect of carbachol, applied to the peri-LC alpha. The present data indicate that alpha2 adrenoceptors located in the caudal peri-LC alpha play a critical role in inhibitory mechanisms of PS generation.