Definitive evidence for the existence of morphological plasticity in the external zone of the median eminence during the rat estrous cycle: implication of neuro-glio-endothelial interactions in gonadotropin-releasing hormone release
Definitive evidence for the existence of morphological plasticity in the external zone of the median eminence during the rat estrous cycle: implication of neuro-glio-endothelial interactions in gonadotropin-releasing hormone release
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DOI：
10.1016/s0306-4522(99)00383-8
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发表时间：
1999-10
期刊：
影响因子：
3.3
通讯作者：
V. Prévot;D. Croix;S. Bouret;S. Dutoit;G. Tramu;G. Stefano;J. Beauvillain
中科院分区：
文献类型：
--
作者：
V. Prévot;D. Croix;S. Bouret;S. Dutoit;G. Tramu;G. Stefano;J. Beauvillain
尽管进行了大量的研究，但从未报道过有关促性腺激素释放激素系统的正中隆起外部区域的形态可塑性。在本研究中，我们通过电子显微镜观察连续超薄切片上的单个促性腺激素释放激素免疫反应性神经末梢，研究下丘脑正中隆起外部区域的促性腺激素释放激素神经末梢和/或单性细胞的动态转变是否发生在大鼠动情周期期间。雌性大鼠在发情间期 16 时处死 (n = 3)，即当雌激素水平处于基础水平且促性腺激素释放激素释放较低时，以及在发情前期 16 时处死 (n = 4)，即当雌激素水平达到峰值且排卵前促性腺激素释放激素激增时。我们的结果表明，在发情前期大鼠的正中隆起中，观察到 12±2% 的促性腺激素释放激素神经末梢与实质基底层（即毛细血管周围空间）发生物理接触。在从发情间期 II 大鼠获得的中位隆起中，没有观察到接触。在发情前期，促性腺激素释放激素神经末梢和基底层之间的大量物理接触通过基底层的外翻和/或促性腺激素释放激素神经末梢的新兴过程而发生。对基底层外翻的量化显示，在发情前期，基底层的外观至少是两倍弯曲。这些结果首次证明正中隆起外部区域存在动态塑性变化，使促性腺激素释放激素神经末梢在发情前期当天接触毛细血管周围空间，从而促进神经激素释放到垂体门静脉血液中。
Despite intense investigation, the demonstration of morphological plasticity in the external zone of the median eminence concerning the gonadotropin-releasing hormone system has never been reported. In this study, we investigate whether dynamic transformations of the gonadotropin-releasing hormone nerve terminals and/or tanycytes in the external zone of the median eminence of the hypothalamus occurred during the rat estrous cycle, by following individual gonadotropin-releasing hormone-immunoreactive nerve terminals on serial ultrathin sections observed by electron microscopy. Female rats were killed at 16.00 diestrus II (n=3), i.e. when estrogen levels are basal and gonadotropin-releasing hormone release is low, and at 16.00 proestrus (n=4), i.e. when estrogen levels peak and the preovulatory gonadotropin-releasing hormone surge occurs. Our results show that, in the median eminence obtained from proestrus rats, 12±2% of the gonadotropin-releasing hormone nerve terminals were observed to make physical contact with the parenchymatous basal lamina, i.e. the pericapillary space. In the median eminence obtained from diestrus II rats, no contacts were observed. On proestrus, numerous physical contacts between gonadotropin-releasing hormone nerve terminals and the basal lamina occurred by evagination of the basal lamina and/or by emerging processes from gonadotropin-releasing hormone nerve terminals. The quantification of the evagination of the basal lamina revealed that the basal lamina was at least twofold more tortuous in appearance during proestrus. These results demonstrate for the first time the existence of dynamic plastic changes in the external zone of the median eminence, allowing gonadotropin-releasing hormone nerve terminals to contact the pericapillary space on the day of proestrus, thus facilitating the release of the neurohormone into the pituitary portal blood.