Participation of the Endocannabinoid System in the Effect of TNF- on Hypothalamic Release of Gonadotropin-Releasing Hormone JAVIER FERNANDEZ-SOLARI, a JUAN P. PRESTIFILIPPO, a STEFAN R. BORNSTEIN, b SAMUEL M. MCCANN, a AND VALERIA RETTORI a a Centro de Estudios Farmacol´ ogicos y Bot ´ anicos, Consejo Nacional de Investigaciones Cient´ ıficas y T´ ecnicas (CEFYBO-CONICET-UBA), Paraguay 2155, (1121), Buenos Aires, Argentina b Department of Medicine, Carl Gustav Carus University Hospital, University of Dresden, 01307 Dresden, Germany ABSTRACT: It is known that Δ 9 -tetrahydrocannabinol (THC), the major active ingredient of marijuana, can suppress reproductive function. Also, we reported previously that the endocannabinoid, anandamide (AEA), inhibited gonadotropin-releasing hormone (LHRH) release from medial basal hypothalamus (MBH) of male rats incubated in vitro as well as reduced plasma LH levels after i.c.v. AEA injections into the cerebral lateral ventricle. On the other hand, it is known that during endotox- emia the hypothalamic gonadotropin axis is inhibited. Therefore, the aim of the present study was to determine whether the effect of TNF- , a proinflammatory cytokine induced by lipopolysaccharide (LPS) that inhibits LHRH release, is mediated by the activation of the endocannabi- noid system. The intraperitoneal injection of LPS (5 mg/kg) as well as the i.c.v. injection of tumor necrosis factor- (TNF- ) (100 ng/rat) in- creased significantly the AEA synthesis measured ex vivo in MBHs re- moved 3 h after the treatments. To examine the possibility that TNF- also acted by increasing the synthesis of AEA that was released and ac- tivated the CB1-r followed by inhibition of LHRH release, we measured the effect of TNF- on the AEA synthase activity in MBHs incubated in vitro. As expected, we found that TNF- (2.9 × 10 −9 M) increased the AEA synthesis. Second, we showed that TNF- reduced significantly the forskolin-stimulated LHRH release and that the CB1-r antagonist AM251 (10 −5 M) blocked that inhibition, supporting the hypothesis that TNF- inhibits LHRH release, acting at least in part by activating the en- docannabinoid system. Therefore, our data demonstrate a key role for the Address for correspondence: Valeria Rettori, CEFYBO-CONICET-UBA, Paraguay 2155, (1121), Buenos Aires, Argentina. Voice: 54-11-4508-3680; fax: 54-11-4508-3680. e-mail: vrettori@yahoo.com Ann. N.Y. Acad. Sci. 1088: 238–250 (2006). C  2006 New York Academy of Sciences. doi: 10.1196/annals.1366.008 238