The central part of the medial preoptic nucleus (MPNc) is associated with sexual arousal induction in male rats. However, it is largely unclear how males are sexually aroused and achieve their first copulation. We previously reported that more MPNc neurons activate during the first copulation than the second copulation. In this study, to explore the molecules responsible for sexual arousal induction, we performed DNA microarray of the MPNc in sexually naive males and males after they copulated for their first and second times. We then performed quantitative PCR analyses to validate the results of the DNA microarray. Six genes were identified. Their expression increased following copulation and was higher in males after they copulated for the first time than after the second time. The genes encode transcription factors (Fos, Nfil3, and Nr4a3), a serine/threonine kinase (Sik1), an antioxidant protein (Srxn1), and a neuropeptide precursor VGF (Vgf), which may be the candidate genes responsible for sexual arousal induction. We examined the effects of Vgf knockdown in the MPNc on sexual partner preference and sexual behavior in sexually inexperienced and experienced males to determine the role of VGF in sexual arousal induction. A preference for estrous female rats was reinforced, and the latency of mount and intromission became short after sexually inexperienced males copulated for the first time. However, Vgf knockdown disrupted these phenomena. Vgf knockdown did not have any significant effect in sexually experienced males. VGF-derived neuropeptides presumably serve as an effector molecule to increase sexual activity following sexual arousal induction.
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