THE HABENULA AND PAIN - REPEATED ELECTRICAL-STIMULATION PRODUCES PROLONGED ANALGESIA BUT LESIONS HAVE NO EFFECT ON FORMALIN PAIN OR MORPHINE ANALGESIA

Recent studies have found that electrical stimulation of the habenula or microinjection of morphine into it reduces pain in several pain tes ts. The present study explored additional properties of the habenula. Expt. 1 examined the influence of the duration of stimulation on the d uration of poststimulation analgesia in the formalin test. Expt. 2 was carried out to determine whether destruction of the habenula would af fect either baseline pain levels or analgesia produced by morphine adm inistered systemically in the formalin test. The results showed that t he duration of analgesia is related to the duration of electrical stim ulation. However, habenular lesions did not affect baseline pain level s or morphine analgesia. These studies support earlier evidence that m anipulation of the habenula can produce analgesia, but suggest that it is not tonically active in modulating pain or necessary for the analg esic effects of systemically administered morphine.