Ushimado Marine Institute (UMI), Graduate School of Natural Science and Technology, Okayama University, Ushimado, Setouchi, Okayama 701-4303, Japan; Department of Biological Sciences, Faculty of Science, Kanagawa University, Hiratsuka, Kanagawa 259-1293, Japan.
Ushimado Marine Institute (UMI), Graduate School of Natural Science and Technology, Okayama University, Ushimado, Setouchi, Okayama 701-4303, Japan; Department of Anatomy, Kawasaki Medical School, Kurashiki, Okayama 701-0192, Japan.
Curr Biol. 2021 Jan 11;31(1):103-114.e5. doi: 10.1016/j.cub.2020.09.089. Epub 2020 Oct 29.
Oxytocinergic neurons in the paraventricular nucleus of the hypothalamus that project to extrahypothalamic brain areas and the lumbar spinal cord play an important role in the control of erectile function and male sexual behavior in mammals. The gastrin-releasing peptide (GRP) system in the lumbosacral spinal cord is an important component of the neural circuits that control penile reflexes in rats, circuits that are commonly referred to as the "spinal ejaculation generator (SEG)." We have examined the functional interaction between the SEG neurons and the hypothalamo-spinal oxytocin system in rats. Here, we show that SEG/GRP neurons express oxytocin receptors and are activated by oxytocin during male sexual behavior. Intrathecal injection of oxytocin receptor antagonist not only attenuates ejaculation but also affects pre-ejaculatory behavior during normal sexual activity. Electron microscopy of potassium-stimulated acute slices of the lumbar cord showed that oxytocin-neurophysin-immunoreactivity was detected in large numbers of neurosecretory dense-cored vesicles, many of which are located close to the plasmalemma of axonal varicosities in which no electron-lucent microvesicles or synaptic membrane thickenings were visible. These results suggested that, in rats, release of oxytocin in the lumbar spinal cord is not limited to conventional synapses but occurs by exocytosis of the dense-cored vesicles from axonal varicosities and acts by diffusion-a localized volume transmission-to reach oxytocin receptors on GRP neurons and facilitate male sexual function.
下丘脑室旁核中的催产素能神经元投射到下丘脑外脑区和腰骶脊髓，在哺乳动物的勃起功能和雄性性行为控制中发挥重要作用。腰骶脊髓中的胃泌素释放肽（GRP）系统是控制大鼠阴茎反射的神经回路的重要组成部分，这些回路通常被称为“脊髓射精发生器（SEG）”。我们研究了 SEG/GRP 神经元与下丘脑-脊髓催产素系统在大鼠中的功能相互作用。在这里，我们表明 SEG/GRP 神经元表达催产素受体，并在雄性性行为期间被催产素激活。鞘内注射催产素受体拮抗剂不仅会减弱射精，还会影响正常性行为中的预射精行为。对腰骶脊髓钾刺激急性切片的电子显微镜观察表明，催产素-神经垂体素免疫反应在大量神经分泌致密核心囊泡中被检测到，其中许多囊泡位于轴突末梢的质膜附近，在这些轴突末梢中看不到电子透明微囊泡或突触膜增厚。这些结果表明，在大鼠中，腰骶脊髓中的催产素释放不仅限于传统突触，而是通过轴突末梢致密核心囊泡的胞吐作用发生，并通过扩散（局部容积传递）作用于 GRP 神经元上的催产素受体，促进雄性性功能。
