Habenulo-interpeduncular lesions: the effects on pain sensitivity, morphine analgesia and open-field behavior in rats

The lesions of medial habenular nuclei increased the pain sensitivity, enhanced the analgesic activity of morphine and slightly activated the behavior. The lesion of fasciculus retroflexus, a pathway connecting habenular nuclei with interpeduncular nucleus enhanced the pain sensitivity less markedly, did not change the efficacy of morphine analgesia, but significantly increased the activity of animals. The lesion of interpeduncular nucleus influenced the pain sensitivity to a smallest degree, did not change the analgesic activity of morphine, but dramatically increased the activity of animals. The activation did not resemble the aimless excitation of amphetamine-treated or raphe-lesioned rats, and no signs of increased emotionality or irritability were noted. The results are interpreted as an evidence of habenulo-interpenduncular complex being a part of a system, involved in the regulation of behavioral activity and the sensitivity to the aversive stimuli. These functions are in all probability mediated partly through substance P and met-enkephalin containing neurons, present in these structures.