Jansen H T, Hileman S M, Lubbers L S, Kuehl D E, Jackson G L, Lehman M N
Department of Cell Biology, University of Cincinnati College of Medicine, Ohio 45267, USA.
Biol Reprod. 1997 Mar;56(3):655-62. doi: 10.1095/biolreprod56.3.655.
The final common pathway controlling reproductive function in vertebrates is the GnRH neuron and its projection to the median eminence (ME), site of peptide release into the pituitary portal system. GnRH neurons are widely distributed; therefore we sought to test the hypothesis that those projecting to the ME are located in specific regions. We used as a model the sheep, a species in which a great deal of information regarding the physiology of GnRH secretion is known. To identify cells projecting to the ME (i.e., neuroendocrine neurons), ewes (n = 10) received injections into the ME of neuronal tract-tracing compounds: cholera toxin-beta subunit (CT-beta) or one of two fluorescent compounds (rhodamine isothiocyanate or fluorescein-conjugated dextran). Forty-eight h later, animals were perfused intracranially and their brains were processed for immunocytochemical localization of GnRH and CT-beta using a dual-immunofluorescent procedure or by single-label immunofluorescent visualization of GnRH combined with direct visualization of fluorescent tracers. Small, well-circumscribed injections into the ME were made successfully in 6 of 10 animals, and these overlapped the location of GnRH terminals and fibers. Neuroendocrine GnRH neurons (those GnRH neurons containing retrogradely transported tracer) were identified throughout their previously reported range: within the diagonal band of the Broca/medial septal region, medial preoptic area (MPOA), anterior hypothalamic area, and medial basal hypothalamus. Although the absolute number of neuroendocrine GnRH neurons varied by region, the percentage of the total GnRH population within each of these areas that was retrogradely labeled did not differ (p > 0.05). Injections placed unilaterally within the ME labeled a similar proportion of GnRH cells both ipsilateral and contralateral to the injection site in all areas except the MPOA, where ipsilaterally labeled cells were approximately twice as numerous as those labeled contralaterally. Injections that missed the ME and were placed either into the third ventricle or into the arcuate nucleus labeled only 0.5% and 4-11% of GnRH neurons, respectively. These results do not support the hypothesis that in the ewe, GnRH neurons projecting to the ME are localized to specific regions. Thus, we postulate that GnRH release into the hypophyseal portal system reflects the output of GnRH neurons located in multiple areas.
脊椎动物中控制生殖功能的最终共同途径是促性腺激素释放激素（GnRH）神经元及其向正中隆起（ME）的投射，正中隆起是肽释放到垂体门脉系统的部位。GnRH神经元分布广泛；因此，我们试图验证投射到ME的神经元位于特定区域这一假说。我们以绵羊为模型，绵羊是一种已知大量关于GnRH分泌生理学信息的物种。为了识别投射到ME的细胞（即神经内分泌神经元），给母羊（n = 10）向ME注射神经束示踪化合物：霍乱毒素β亚基（CT-β）或两种荧光化合物之一（异硫氰酸罗丹明或荧光素偶联葡聚糖）。48小时后，对动物进行颅内灌注，并使用双免疫荧光程序或通过GnRH的单标记免疫荧光可视化结合荧光示踪剂的直接可视化对其大脑进行处理，以进行GnRH和CT-β的免疫细胞化学定位。在10只动物中的6只成功地向ME进行了小的、界限清楚的注射，这些注射与GnRH终末和纤维的位置重叠。在先前报道的整个范围内都鉴定出了神经内分泌GnRH神经元（即那些含有逆行转运示踪剂的GnRH神经元）：在布罗卡斜带/内侧隔区、内侧视前区（MPOA）、下丘脑前区和下丘脑内侧基底部。尽管神经内分泌GnRH神经元的绝对数量因区域而异，但这些区域中每个区域内被逆行标记的GnRH总数的百分比并无差异（p>0.05）。除MPOA外，在所有区域中，单侧注射到ME的标记物在注射部位同侧和对侧标记的GnRH细胞比例相似，在MPOA中，同侧标记的细胞数量大约是对侧标记细胞的两倍。错过ME并注射到第三脑室或弓状核的标记物分别仅标记了0.5%和4 - 11%的GnRH神经元。这些结果不支持在母羊中投射到ME的GnRH神经元定位于特定区域这一假说。因此，我们推测GnRH释放到垂体门脉系统反映了位于多个区域的GnRH神经元的输出。
