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 autoreceptors located in the dorsal and median raphe nuclei on the stimulant effect of cocaine on locomotor activity, rears and head bobs in female Glaxo Wistar rats. Cocaine was administered at a submaximal dose of 15 mg/kg i.p. to enable 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 administration of cocaine 60 min later. WAY 100635 microinjected in the dorsal or median raphe nuclei did not consistently alter the locomotor activity and the number of rears of saline-treated animals. Microinjection of WAY100635 in the dorsal raphe nucleus potentiated cocaine-induced locomotor activity and the number of head bobs. The number of rears induced by cocaine was not significantly altered by WAY100635 microinjected in the dorsal raphe nucleus. In contrast, microinjection of WAY100635 in the median raphe nucleus did not alter the stimulant effect of cocaine on locomotor activity, rears or head bobs. It may be suggested from these results that stimulation of somatodendritic 5-HT1A autoreceptors located in the dorsal raphe nucleus mediates an inhibitory effect on cocaine-induced locomotor activity and head bobs, whereas somatodendritic 5-HT1A autoreceptors in the median raphe nucleus are not involved in the inhibitory role of 5-HT on the stimulant effect of cocaine on locomotor activity and head bobs. A differential involvement of the midbrain raphe nuclei may exist controlling the stimulant effect of cocaine on locomotor activity and head bobs.