The gastrin-releasing peptide system in the spinal cord mediates masculine sexual function
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The lumbar spinal segments are of particular interest because they are sexually dimorphic and contain several neuronal circuits that are important in eliciting male sexual responses such as erection and ejaculation. Gastrin-releasing peptide (GRP) is a member of the bombesin-like peptide family first isolated from the porcine stomach. A collection of neurons in the lumbar spinal cord (L3–L4 level) of male rats projects to the lower lumbar spinal cord (L5–L6 level), releasing GRP onto somatic and autonomic centers known to regulate male sexual reflexes. All these target neurons express and localize specific receptors for GRP. This system of GRP neurons is sexually dimorphic, being prominent in male rats but vestigial in females. The system is completely feminine in genetically XY rats with a dysfunctional androgen receptor gene, demonstrating the androgen-dependent nature of the dimorphism. Pharmacological stimulation of GRP receptors in this spinal region remarkably restores sexual reflexes in castrated male rats. Exposure of male rats to a severe traumatic stress decreases the local content and the axonal distribution of GRP in the lumbar spinal cord and results in an attenuation of penile reflexes in vivo. Administration of a specific agonist for GRP receptors restores penile reflexes in the traumatic stress-exposed male rats. This review summarizes findings on this recently identified spinal GRP system, which may be vulnerable to stress, that controls male reproductive function. The identification of a male-specific neuronal system regulating sexual functions offers new avenues for potential therapeutic approaches to masculine reproductive dysfunction.
KeywordsGastrin-releasing peptide Lumbar spinal cord Androgens Male sexual function
I thank Dr. Damian G. Zuloaga (University of Arizona College of Medicine-Phoenix, AZ, USA) for valuable discussions, reading the manuscript and collaboration. I am grateful to Drs. Mitsuhiro Kawata, Ken-Ichi Matsuda, Keiko Takanami, Hisayuki Hongu, Nobuko Nishiura, Etsuko Wada, Keiji Wada, Tatsuo Arii, Tatsuya Sakamoto, Cynthia L. Jordan and S. Marc Breedlove for their valuable discussions and collaborations. This work was supported by Grants-in-Aid Scientific Research [Encouragement of Young Scientists (A): no. 21680031, (B): no. 19700319] from the Ministry of Education, Science, Sports, Culture and Technology, Japan; by Grants-in-Aid for Young Scientists (Start-up) from Okayama University, Japan; by The Naito Memorial Grant for Natural Science Researches, Japan; by The Uehara Memorial Foundation, Japan; by The Inamori Foundation, Japan; by Narishige Neuroscience Research Foundation, Japan; and by Co-operative Study by High-voltage Electron Microscopy (H-1250M) from the National Institute for Physiological Sciences, Okazaki, Japan. All experimental procedures for the author’s research project cited in the present review have been authorized by the Committee for Animal Research, Kyoto Prefectural University of Medicine and Okayama University, Japan and/or the Institutional Animal Care and Use Committee of Michigan State University, MI, USA. The author is a recipient of the Incitement Award of the Japanese Association of Anatomists in the fiscal year 2009, and a part of the present work was presented at the 115th annual meeting in Morioka, Iwate, Japan, 28–30 March 2010.
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