The influence of electrical stimulation on dorsal raphe nucleus with different current intensities on morphine-induced conditioned place preference in male rats

Introduction: The dorsal raphe nucleus (DRN) influences a wide range of behavioral and physiological processes. The purpose of the present study was to test the effects of electrical stimulation of the DRN with different current intensities on morphine-induced conditioned place preference (CPP). Materials and methods: Male Wistar rats were divided for experimental groups (n = 7). Stimulating electrodes were stereotaxically implanted into the DRN in anesthetized rats. We investigated the influences of electrical stimulation of the DRN with different current intensities with ineffective and effective dose of morphine (0.5 and 2.5 mg/kg, respectively) on morphine-induced CPP. Result: Subcutaneous administration of morphine 2.5 mg/kg produced significant CPP in comparison with saline group. The stimulation of the DRN with different current intensities (10, 25, 50 and 100 mu A) in combination with an effective dose of morphine did not show significant differences on acquisition phases, whereas there were significant decreases on expression phases versus to the morphine group on CPP only in current intensity 100 mu A. The stimulation of the DRN with different current intensities in combination with an ineffective dose of morphine showed significant increases in current intensities (50 and 100 mu A) on acquisition phases of CPP, but did not show significant differences on expression phases versus to the morphine group on CPP. Conclusion: It is possible that electrical stimulation of the DRN with changes in concentration of serotonin or involving other transmitters such as glutamate and GABA would be involved with these changes of CPP. (C) 2015 Institute of Pharmacology, Polish Academy of Sciences. Published by Elsevier Sp. z.o.o. All rights reserved.