en Physiology Physiology Original Research: Basic Science in Medicine Original Research: Basic Science in Medicine In vivo microdialysis was used to study the effects of morphine on glutamate release from the ventral tegmentum area (VTA) in freely moving rats. Intraperitoneal (i.p.) injection of acute and repeated morphine at increasing doses significantly enhanced glutamate release. Only a minor tolerance developed to this dosage of morphine. AP-S (2-amino-5-phosphonovaleric acid, 0.5 mg/kg i.p.), a NMDA receptor antagonist, given 20 min before each repeated morphine injection, did not have a significant effect on the stimulated glutamate release . Conversely, injection of CNQX (6-cyano-7-nitroquinoxaline-2, 3-dione, 0.5 mg/kg i.p.), an AMPA receptor antagonist, 20 min before each morphine dose was found to markedly inhibit morphine-induced glutamate release in the VTA. In all experiments, glutamate release reduced by time. These results show for the first time that acute and repeated injection of morphine stimulates glutamate release in the conscious rat VTA via AMPA receptors. Morphine, Glutamate, V TA, Microdialysis. 225 231 http://mjiri.iums.ac.ir/browse.php?a_code=A-10-298-145&slc_lang=en&sid=1 H ALAEI alaei@med.mui.ac.ir 20031947532846003741 20031947532846003741 Yes From theDepartment of Physiology, University of Esfahan, Iran, theDepartment of Pharmacology and Toxicology, University of Kuopio, Finland M HUOTARI 20031947532846003742 20031947532846003742 No theDepartment of Pharmacology and Toxicology, University of Kuopio, Finland PT PIEPPONEN 20031947532846003743 20031947532846003743 No the Unit of Pharmacology and Toxicology, Department of Pharmacy, University of Helsinki, Helsinki, Finland, L AHTEE 20031947532846003744 20031947532846003744 No the Unit of Pharmacology and Toxicology, Department of Pharmacy, University of Helsinki, Helsinki, Finland, O HANNINEN 20031947532846003745 20031947532846003745 No Department of Physiology, University of Kuopio, Finland PT MANNISTO 20031947532846003746 20031947532846003746 No theDepartment of Pharmacology and Toxicology, University of Kuopio, Finland