Effects of Electrical Stimulation of Nucleus Raphe Dorsalis on Initiation of Morphine Self-Administration in Rats

Recent neurochemical studies suggest that alterations in functions of the central neurotransmitters may be involved in addiction. Serotonin (5-HT), dopamine (DA) and endogenous opiate are the most important neurotransmitters involved in addiction. Nucleus raphe dorsalis (NRD) on the other hand is the important site that secrete or modulate these substances. Release of 5-HT can be evoked by focal electrical stimulation of NRD. In this study electrical stimulation (30 min: pulse 0.5 ms, 150 A, 20 Hz) of the antero-dorsal part of the nucleus raphe dorsalis produced significant decrease in initiation of morphine self-administration during 10 consecutive 2-h sessions. During all sessions lever-pressing behavior was measured. After the last test session, morphine withdrawal syndrome signs (wet dog shakes, jumping, writhing and diarrhea) in the naloxone-induced behavior, were measured. The results show that these withdrawal syndrome signs are decreased by application of electrical stimulation of NRD. It is concluded that electrical stimulation of NRD enhances the serotonergic and endogenous opiate transmission, and this activation might be involved in reduction of craving for morphine.