The involvement of opioid peptides in the neural regulation of luteinizing hormone secretion in the female rat

Date of Completion

January 1997


Biology, Neuroscience|Biology, Animal Physiology




The first experiment determined whether changes in the activity of norepinephrine (NE) or dopamine (DA) neurons modulate the suppression of luteinizing hormone (LH) secretion due to activation of $\mu$-opioid receptors in the medial preoptic-anterior hypothalamic area (MPOA-AHA) in the ovariectomized rat. Utilizing push-pull perfusion, activation of MPOA-AHA $\mu$-opioid receptors with DAGO inhibited LH release but perfusate NE levels did not change. Inhibition of NE synthesis or blockade of DA receptors had no effect on the DAGO-induced suppression of LH release. This study demonstrated that NE or DA neurons do not mediate the inhibition of LH secretion in response to activation of MPOA-AHA $\mu$-opioid receptors.^ The second experiment examined whether blockade of MPOA $\kappa$-opioid receptors on the afternoon of proestrus could prematurely evoke an ovulatory LH surge, and if so, whether NE was involved. LH surges begin in our colony between 1530-1630 h. Perfusion of the MPOA between 1030-1350 h with nor-binaltorphimine (nor-BNI) produced a large increase in LH release beginning between 1230-1330 h (an advance of 3 hours), and ovulation. NE synthesis inhibition with FLA-63 partially reduced, and blockade of $\alpha$-adrenergic receptors with PBZ completely prevented the occurrence of the nor-BNI-induced LH surge. PBZ also prevented the normal afternoon LH surge. MPOA perfusate NE levels did not increase during the nor-BNI-induced or normal afternoon LH surges. Thus blockade of MPOA $\kappa$-opioid receptors prematurely evokes an ovulatory LH surge. Furthermore, the nor-BNI-induced and normal afternoon LH surges are dependent on the proper functioning of central noradrenergic neurons, but do not involve increased NE release within the MPOA.^ The final study examined whether a decrease in MPOA $\kappa$-opioid tone normally occurs on the afternoon of proestrus. In pentobarbital-anesthetized rats, nor-BNI perfusion of the MPOA was 25% less effective in increasing LH release on the afternoon of proestrus compared to the late morning. However, this difference was not significant. Thus, this finding is only suggestive of a decrease in MPOA $\kappa$-opioid tone normally occurring on the afternoon of proestrus. ^