Horvath T L
Department of Obstetrics and Gynecology, Yale University School of Medicine, New Haven, Connecticut 06520, USA.
Endocrinology. 1997 Mar;138(3):1312-20. doi: 10.1210/endo.138.3.4976.
The key role of the suprachiasmatic nucleus in the diurnal regulation of anterior pituitary hormone secretions, including PRL, is well established. However, the pathway via suprachiasmatic signals reach the pituitary is ill defined. To determine whether suprachiasmatic efferents innervate neuroendocrine cells, the anterograde tracer, Phaseolus vulgaris leukoagglutinin, was injected iontophoretically into the suprachiasmatic nucleus in parallel with ip administration of fluorogold (20 mg/BW in saline). After visualization of anterogradely labeled processes with a dark blue chromogen. Vibratome sections were immunostained for fluorogold. As fluorogold labeling resulted in dense immunopositive granules without diffuse cytoplasmic labeling, selected sections were further immunostained for cytoplasmic tyrosine hydroxylase (dopamine). Anterogradely labeled suprachiasmatic efferents were observed in the medial preoptic area, periventricular regions, and the lateral aspects of the arcuate and ventromedial nuclei of the hypothalamus, whereas the median eminence and organum vasculosum laminae terminalis lacked labeled suprachiasmatic projections. All of the aforementioned regions contained a high number of cells immunoreactive for fluorogold. However, immunolabeling for fluorogold revealed no retrogradely labeled (ergo neuroendocrine) cells in the suprachiasmatic nucleus. Retrogradely labeled cells in all of these hypothalamic sites, with the exception of the median eminence and organum vasculosum laminae terminalis, were targets of suprachiasmatic nucleus axon terminals. In the preoptic area, anterior hypothalamus, periventricular area, and arcuate nucleus, subpopulations of dopamine cells were retrogradely labeled. In all of these areas, both retrogradely labeled and nonlabeled dopamine cells were frequently found to be in contact with dark blue, anterogradely labeled suprachiasmatic efferents. Electron microscopic examination confirmed the putative connections to be synaptic. This experiment provided evidence that the circadian pacemaker suprachiasmatic nucleus sends efferents onto neuroendocrine cells, but has no contacts with fenestrated capillaries. It was found that a population of median eminence-projective cells targeted by suprachiasmatic axons in the hypothalamus contains dopamine. These observations indicate no direct effect of the circadian pacemaker on the anterior hypophysis, but offer an indirect pathway via circadian signals, mediated by hypothalamic neural systems, that may regulate pituitary hormone secretion, in particular PRL.
视交叉上核在包括催乳素在内的垂体前叶激素分泌的昼夜调节中所起的关键作用已得到充分证实。然而，视交叉上核信号到达垂体的途径尚不清楚。为了确定视交叉上核的传出神经是否支配神经内分泌细胞，将顺行示踪剂菜豆白细胞凝集素通过离子电渗法注入视交叉上核，同时腹腔注射荧光金（20mg/体重，溶于生理盐水中）。在用深蓝色显色剂使顺行标记的突起可视化后，对振动切片进行荧光金免疫染色。由于荧光金标记产生密集的免疫阳性颗粒而无弥漫性细胞质标记，因此对选定切片进一步进行细胞质酪氨酸羟化酶（多巴胺）免疫染色。在视前内侧区、室周区域以及下丘脑弓状核和腹内侧核的外侧观察到顺行标记的视交叉上核传出神经，而正中隆起和终板血管器缺乏标记的视交叉上核投射。上述所有区域都含有大量对荧光金呈免疫反应的细胞。然而，荧光金免疫标记显示视交叉上核中没有逆行标记的（即神经内分泌）细胞。除正中隆起和终板血管器外，所有这些下丘脑部位的逆行标记细胞都是视交叉上核轴突终末的靶细胞。在视前区、下丘脑前部、室周区和弓状核中，多巴胺能细胞亚群被逆行标记。在所有这些区域，经常发现逆行标记和未标记的多巴胺能细胞与深蓝色的、顺行标记的视交叉上核传出神经接触。电子显微镜检查证实这些假定的连接是突触连接。该实验提供了证据，即昼夜节律起搏器视交叉上核向神经内分泌细胞发送传出神经，但与有窗孔的毛细血管没有接触。研究发现，下丘脑视交叉上核轴突靶向的一群正中隆起投射细胞含有多巴胺。这些观察结果表明昼夜节律起搏器对垂体前叶没有直接影响，但提供了一条通过下丘脑神经系统介导的昼夜节律信号的间接途径，该途径可能调节垂体激素分泌，尤其是催乳素。
