NITRIC OXIDE MEDIATES GLUTAMATE-EVOKED DOPAMINE RELEASE IN THE MEDIAL PREOPTIC AREA J. M. DOMINGUEZ, 1 J. W. MUSCHAMP, J. M. SCHMICH AND E. M. HULL* Department of Psychology, University at Buffalo, The State University of New York, B71 Park Hall, Buffalo, NY 14260-4110, USA Abstract—Dopamine (DA) release in the medial preoptic area (MPOA) of the hypothalamus is an important facilitator of male sexual behavior. The presence of a receptive female increases extracellular DA in the MPOA, which increases further during copulation. However, the neurochemical events that mediate the increase of DA in the MPOA are not fully understood. Here we report that glutamate, reverse- dialyzed into the MPOA, increased extracellular DA, which returned to baseline after the glutamate was removed. This increase was prevented by co-administration of the nitric oxide synthase inhibitor N G -nitro-L-arginine methyl ester (L- NAME), but not by the inactive isomer, Nw-nitro-D-arginine methyl ester (D-NAME). In contrast, extracellular concentra- tions of the major metabolites of DA were decreased by glutamate, suggesting that the DA transporter was inhibited. These decreases were also inhibited by L-NAME, but not D-NAME. These results indicate that glutamate enhances extracel- lular DA in the MPOA, at least in part, via nitric oxide activity. Therefore, glutamatergic stimulation of nitric oxide synthase may generate the female-induced increase in extracellular DA in the MPOA, which is important for the expression of male sexual behavior. © 2004 IBRO. Published by Elsevier Ltd. All rights reserved. Key words: sexual behavior, NMDA, dopamine transporter, microdialysis. The medial preoptic area (MPOA) of the hypothalamus is critical for the control of male sexual behavior in all verte- brate species that have been tested (reviewed in Hull et al., 2002). Although dopamine (DA) in the nucleus accumbens enhances activation for numerous motivated behaviors, including sexual behavior, DA in the MPOA is important for focusing motivation on specifically sexual activity and for coordinating genital and somatomotor responses (re- viewed in Hull, 1995; Hull et al., 2002). DA is released in the MPOA as soon as a male rat detects the presence of an estrous female and during copulation (Hull et al., 1995). Both basal (Lorrain and Hull, 1993) and copulation-stimu- lated (Lorrain et al., 1996) DA release in the MPOA is regulated, at least in part, by nitric oxide (NO). However, factors “upstream” of NO have not been determined. Glutamate regulates the release of DA in several brain regions both in vitro and in vivo (Whitton, 1997; Takahata and Moghaddam, 1998; Verma and Moghaddam, 1998; Shimazoe et al., 2002; Howland et al., 2002; Avshalumov et al., 2003; Katayama et al., 2003; Morikawa et al., 2003). Glutamate–DA interactions have been implicated in the regulation of various behaviors and behavioral disorders, including drug addiction (reviewed in Kelley and Berridge, 2002), schizophrenia (reviewed in Carlsson et al. 2001; Moghaddam, 2002; Pralong et al., 2002), and Parkinson’s disease (reviewed in Carlsson and Carlsson, 1990; Lange et al., 1997). The present experiments investigated the effects of exogenous glutamate on extracellular DA in the MPOA of male rats. Using in vivo microdialysis, experiment 1 inves- tigated whether reverse dialysis of glutamate through the microdialysis probe would influence extracellular DA and its major metabolites, dihydroxyphenylacetic acid (DOPAC) and homovanillic acid (HVA), in the MPOA of urethane-anesthetized male rats. Experiment 2 investi- gated whether an NO synthase (NOS) antagonist [N G - nitro-L-arginine methyl ester (L-NAME)] or its inactive iso- mer [Nw-nitro-D-arginine methyl ester (D-NAME)] would alter any glutamate-evoked effects on DA, DOPAC, and HVA. EXPERIMENTAL PROCEDURES Subjects Adult male Long-Evans/Blue Spruce rats (Harlan, Indianapolis, IN, USA) were housed individually in large plastic cages. Rats were housed in a climate-controlled room, on a 14/10 h light/dark cycle, with lights off at 11:00 h and on at 21:00 h. Food and water were available ad libitum. All procedures were in accordance with the National Institutes of Health Guidelines for the Use of Animals, and were approved by the local Institutional Animal Care and Use Committee. All efforts were made to minimize the number of animals used and their suffering. Surgery Animals (approximately 300 g at the time of surgery) were anes- thetized with urethane (Sigma, St. Louis, MO, USA; 1.5 g/kg) dissolved in saline. Animals received probe implants aimed at the MPOA (anterior-posterior, 2.3 mm; medio-lateral, 0.3 mm; dorsal- 1 Present address: University of Cincinnati College of Medicine, De- partment of Cell Biology, Neurobiology and Anatomy, Vontz Center for Molecular Studies, 3125 Eden Avenue, Cincinnati, OH 45267-0521, USA. *Corresponding author. Tel: +1-716-645-3650x671; fax: +1-716-645-3801. E-mail address: emhull@buffalo.edu (E. M. Hull). Abbreviations: aCSF, artificial cerebral spinal fluid; DA, dopamine; D-NAME, Nw-nitro-D-arginine methyl ester; DOPAC, dihydroxyphenyl- acetic acid; HPLC-EC, high performance liquid chromatography with electrochemical detection; HVA, homovanillic acid; L-NAME, N G -nitro- L-arginine methyl ester; MPOA, medial preoptic area; NMDA, N-methyl-D-aspartate; NO, nitric oxide; NOS, nitric oxide synthase; RM-ANOVA, repeated measures analysis of variance; TH-ir, tyrosine hydroxylase immunoreactive. Neuroscience 125 (2004) 203–210 0306-4522/04$30.00+0.00 © 2004 IBRO. Published by Elsevier Ltd. All rights reserved. doi:10.1016/j.neuroscience.2004.01.022 203