King J C, Rubin B S
Department of Anatomy and Cellular Biology, Tufts University School of Medicine, Boston, Massachusetts 02111, USA.
Horm Behav. 1994 Dec;28(4):349-56. doi: 10.1006/hbeh.1994.1031.
Luteinizing hormone-releasing hormone (LHRH) release is required for ovulation in mammals. Although evidence for the direct action of gonadal steroids on LHRH neurons has been minimal, their importance in inducing the preovulatory surge of LHRH is unequivocal. We have identified a subgroup of LHRH neurons with progestin receptors in guinea pigs. Given their central position, these neurons may constitute foci of initial activity, which are amplified throughout the population of LHRH neurons, resulting in increased LHRH neurosecretion on the afternoon of proestrus. Additionally, gonadal steroids may regulate LHRH secretion at the level of the terminals. Using immunoelectron microscopy and image analysis, we have illustrated the dramatic influence of gonadal steroids on individual LHRH terminals in the median eminence of rats. Indirectly, gonadal steroids may modulate LHRH release by modulating glial elements. Using double-label fluorescence confocal microscopy, we illustrate that LHRH terminals in the median eminence are encased by end-feet of tanycytes. Acting on glial elements, gonadal steroids may regulate access of LHRH terminals to the basal lamina and influence the amount of the neuropeptide reaching the portal vessels. We propose that during the preovulatory surge, LHRH release is coordinated by synergistic mechanisms operating at the level of particular subgroups of neuronal perikarya and/or discrete regions of the median eminence. These synergistic actions may ensure that LHRH is released in a precipitous fashion, to induce the surge of LH from the pituitary, required for ovulation.
促黄体生成激素释放激素（LHRH）的释放是哺乳动物排卵所必需的。尽管性腺类固醇对LHRH神经元直接作用的证据很少，但它们在诱导LHRH排卵前激增方面的重要性是明确的。我们已经在豚鼠中鉴定出一组具有孕激素受体的LHRH神经元。鉴于它们的中心位置，这些神经元可能构成初始活动的焦点，在整个LHRH神经元群体中被放大，导致发情前期下午LHRH神经分泌增加。此外，性腺类固醇可能在终末水平调节LHRH的分泌。通过免疫电子显微镜和图像分析，我们已经阐明了性腺类固醇对大鼠正中隆起中单个LHRH终末的显著影响。间接而言，性腺类固醇可能通过调节神经胶质成分来调节LHRH的释放。使用双标荧光共聚焦显微镜，我们表明正中隆起中的LHRH终末被伸长细胞的终足包裹。作用于神经胶质成分，性腺类固醇可能调节LHRH终末与基膜的接触，并影响到达门静脉的神经肽量。我们提出，在排卵前激增期间，LHRH的释放是由在神经元胞体的特定亚群水平和/或正中隆起的离散区域协同作用的机制协调的。这些协同作用可能确保LHRH以急剧的方式释放，以诱导垂体释放LH激增，这是排卵所必需的。
