Effects of Temporary Inactivation and Electrical Stimulation of the Dorsal Raphe Nucleus on Morphine-induced Conditioned Place Preference.

Background: The dorsal raphe nucleus (DRN) influences a wide range of behavioral and reward function. In this study, we evaluated electrical stimulation and inactivation of DRN on morphine conditioned place preference (CPP).

Methods: The rats were anesthetised (n = 7 for each group) and the electrode and cannula were implanted into the DRN by stereotaxic instrument. Electrical stimulation (100μA) and reversible inactivation by lidocaine were induced into DRN and then morphine-induced CPP was investigated.

Results: The stimulation of DRN in combination with effective dose of morphine showed a significant decrease only on expression phases 20s (SD 33.7) when compared with morphine group 119.85s (SD 23.7) (One way ANOVA, Tukey's; P = 0.036). Also, this stimulation in combination with ineffective dose of morphine showed a significant increase only on acquisition phases 67.5s (SD 41.2) of CPP compared with morphine group -46s (SD 18.51) (P = 0.034). Also, there were not significant differences in inactivation of DRN by lidocaine on different phase of CPP (P = 0.091) CONCLUSION: It is possible that electrical stimulation of the DRN with changes in concentration of serotonin or involving other transmitters such as glutamate and gamma amino butyric acid (GABA) would be involved to these changes of CPP.