Different behavioral responses of rats to kainate injections into the dorsal and median raphe nuclei.

A local injection of kainic acid (KA) into the dorsal raphe nucleus (NRD) increased the motor activity and produced head shakes, hind limb abduction, forepaw treading and sniffing. This syndrome was antagonized partly by cyproheptadine and completely by naloxone. An injection of KA into the median raphe nucleus (NRM) produced sedation, catalepsy and analgesia, which were accompanied by a decrease in the beta-endorphin immunoreactivity in the mesencephalon. Naloxone completely reversed the behavioral inhibition after KA injections into the NRM, while a pretreatment with cyproheptadine augmented the catalepsy. KA injected into the NRD and NRM depressed the forebrain level of serotonin and slightly elevated that of 5-hydroxyindoleacetic acid. The results demonstrate that besides serotonin the opioid system is also involved in various effects induced by activation of the raphe nuclei.