Modulation of cocaine-induced locomotor activity, rears and head bobs by application of WAY100635 into the dorsal and median raphe nuclei of the rat

The present study investigated the role of somatodendritic 5-HT1A autorecep tors located in the dorsal and median raphe nuclei on the stimulant effect of cocaine on locomotor activity, rears and head bobs in female Glare Wista r rats. Cocaine was administered at a submaximal dose of 15 mg/kg i.p. to e nable either a potentiation or attenuation to be observed. The selective 5- HT1A antagonist WAY100635 (0.21 ng or 21 ng) or saline was microinjected in the dorsal or median raphe nuclei followed by the peripheral administratio n of cocaine 60 min later. WAY100635 microinjected in the dorsal or median raphe nuclei did not consistently alter the locomotor activity and the numb er of rears of saline-treated animals. Microinjection of WAY100635 in the d orsal raphe nucleus potentiated cocaine-induced locomotor activity and the number of head bobs. The number of rears induced by cocaine was not signifi cantly altered by WAY100635 microinjected in the dorsal raphe nucleus. In c ontrast, microinjection of WAY100635 in the median raphe nucleus did not al ter the stimulant effect of cocaine on locomotor activity, rears or head bo bs. It may be suggested from these results that stimulation of somatodendri tic 5-HT1A autoreceptors located in the dorsal raphe nucleus mediates an in hibitory effect on cocaine-induced locomotor activity and head bobs, wherea s somatodendritic 5-HT1A,A autoreceptors in the median raphe nucleus are no t involved in the inhibitory role of 5-HT on the stimulant effect of cocain e on locomotor activity and head bobs. A differential involvement of the mi dbrain raphe nuclei may exist controlling the stimulant effect of cocaine o n locomotor activity and head bobs.