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Orphanin FQ/Nociceptin Is a Physiological Regulator of Prolactin Secretion in Female Rats

Center for Neuroscience, Departments of Zoology (M.C., J.J., D.L., E.S., P.C.) and Mathematics and Statistics (E.M.), Miami University, Oxford, Ohio 45056

Address all correspondence and requests for reprints to: Phyllis Callahan, Center for Neuroscience, Department of Zoology, Miami University, Oxford, Ohio 45056. E-mail: Callahp{at}muohio.edu.

Orphanin FQ/nociceptin (OFQ/N), the most recently identified endogenous opioid peptide, stimulates prolactin secretion in both male and female rats. OFQ/N, however, did not elicit this stimulatory effect through the µ-, -, or -opiate receptor subtype. The role OFQ/N plays in prolactin regulation under physiological conditions and its mechanism of action are not known. The purpose of these studies was to determine the physiological significance and pharmacological specificity of the prolactin secretory response to OFQ/N. In addition, the role of the tuberoinfundibular dopaminergic (TIDA) neurons in mediating this response was examined. Opioid receptor-like-1 (ORL-1) receptors were blocked by pretreatment with compound B (Comp B), a purported OFQ/N antagonist, or receptor synthesis was disrupted by pretreatment with ORL-1 receptor antisense oligonucleotides. The prolactin secretory response to OFQ/N administration in diestrous females was measured. Furthermore, the suckling-induced prolactin response was also determined after Comp B pretreatment. TIDA neuronal activity was quantified in diestrous female rats to determine whether OFQ/N stimulates prolactin release by inhibiting TIDA neurons. OFQ/N significantly inhibited the TIDA neurons by 1 min, preceding the prolactin secretory response. Both Comp B and antisense pretreatment blocked the stimulatory effects of OFQ/N on prolactin release, and Comp B abolished the suckling-induced prolactin response. These studies indicate that OFQ/N is a potent stimulus for prolactin secretion in female rats and that it mediates this effect by rapid and transient inhibition of TIDA neuronal activity. Furthermore, OFQ/N plays a physiologically significant role in the regulation of prolactin secretion during lactation, and it mediates its effects via actions at the ORL-1 receptor subtype.

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				C. D. Foradori, M. Amstalden, L. M. Coolen, S. R. Singh, C. J. McManus, R. J. Handa, R. L. Goodman, and M. N. Lehman Orphanin FQ: Evidence for a Role in the Control of the Reproductive Neuroendocrine System Endocrinology, October 1, 2007; 148(10): 4993 - 5001. [Abstract] [Full Text] [PDF]