FURTHER-STUDIES ON THE SUPPRESSION OF LUTEINIZING-HORMONE RELEASE DUETO ACTIVATION OF MEDIAL PREOPTIC-ANTERIOR HYPOTHALAMIC AREA MU-OPIOIDRECEPTORS

Our laboratory has previously demonstrated that specific activation of mu-opioid receptors in the medial preoptic-anterior hypothalamic area with [D-Ala(2), N Me-Phe(4), Gly-ol(5)]-enkephalin (DAGO) suppresses luteinizing hormone secretion in the ovariectomized rat [29]. In the p resent study, three experiments were undertaken to ascertain whether c hanges in the activity of norepinephrine or dopamine neurons modulate the decrease in luteinizing hormone release in response to DAGO. The f irst experiment utilized push-pull perfusion in conjunction with HPLC to assess in vivo norepinephrine release in the medial preoptic-anteri or hypothalamic area in response to perfusion of this site with DAGO ( 5 mu g/h). DAGO significantly decreased luteinizing hormone release, b ut perfusate norepinephrine levels did not change. In the second exper iment, push-pull perfusion in the medial preoptic-anterior hypothalami c area with cerebrospinal fluid (CSF) or CSF containing DAGO was done in rats pretreated with the norepinephrine synthesis inhibitor, FLA-63 . This drug pretreatment had no effect on the DAGO-induced suppression of luteinizing hormone secretion. In Experiment 3, push-pull perfusio n in the medial preoptic-anterior hypothalamic area with CSF followed by CSF containing DAGO was done in rats pretreated with vehicle, or a dopamine receptor antagonist, either pimozide or d-butaclamol. Neither dopamine receptor antagonist had any effect on the DAGO-induced suppr ession of luteinizing hormone release. Thus, these studies do not supp ort a role for alterations in the activity of norepinephrine or dopami ne neurons in mediating the suppression of luteinizing hormone release in response to activation of mu-opioid receptors in the medial preopt ic-anterior hypothalamic area in the ovariectomized rat. Copyright (C) 1997 Elsevier Science Inc.