Christian H C, Imirtziadis L, Tortonese D
Department of Physiology, Anatomy and Genetics, University of Oxford, Oxford, UK.
J Neuroendocrinol. 2015 Apr;27(4):277-84. doi: 10.1111/jne.12261.
In seasonal mammals living in temperate zones, photoperiod regulates prolactin secretion, such that prolactin plasma concentrations peak during the summer months and are lowest during the winter. In sheep, a short-day breeder, circulating prolactin has important modulatory effects on the reproductive system via inhibitory actions on pituitary gonadotrophs and hypothalamic gonadotrophin-releasing hormone release. The exact cellular mechanisms that account for the chronic hypersecretion of prolactin during the summer is not known, although evidence supports an intrapituitary mechanism regulated by melatonin. Folliculo-stellate (FS) cells are non-endocrine cells that play a crucial role in paracrine communication within the pituitary and produce factors controlling prolactin and gonadotrophin release. The present study examined the morphology of the FS and lactotroph cell populations and their distribution in the sheep pituitary during the annual reproductive cycle. Ovine pituitary glands were collected in the winter (breeding season; BS) and summer (nonbreeding season; NBS) and were prepared for quantitative electron microscopy to assess the effects of season on FS and lactotroph cell density, morphology and distribution, as well as on junctional contacts between cells. It was found that lactotrophs in the NBS are larger in size and contain more numerous PRL granules than lactotrophs in the BS. FS cells were also larger in the NBS compared to BS and showed altered morphology such that, in the BS, long cell processes surrounded clusters of adjacent secretory cells. Although no significant change in the number of junctions was observed between lactotrophs and FS cells, or lactotrophs and gonadotrophs, there was a significant increase in the number of adherens junctions between lactotrophs and between FS cells. These findings demonstrate seasonal plasticity in the morphology of lactotrophs and FS cells that reflect changes in PRL secretion.
在生活于温带的季节性繁殖哺乳动物中，光周期调节催乳素的分泌，使得血浆催乳素浓度在夏季达到峰值，而在冬季降至最低。在绵羊这种短日照繁殖动物中，循环中的催乳素通过对垂体促性腺细胞和下丘脑促性腺激素释放激素释放的抑制作用，对生殖系统具有重要的调节作用。尽管有证据支持一种由褪黑素调节的垂体内部机制，但导致夏季催乳素慢性分泌过多的确切细胞机制尚不清楚。滤泡星状（FS）细胞是非内分泌细胞，在垂体内的旁分泌通讯中起关键作用，并产生控制催乳素和促性腺激素释放的因子。本研究考察了FS细胞和催乳素分泌细胞群体的形态及其在绵羊垂体年度生殖周期中的分布。在冬季（繁殖季节；BS）和夏季（非繁殖季节；NBS）采集绵羊垂体，制备用于定量电子显微镜检查的样本，以评估季节对FS细胞和催乳素分泌细胞的密度、形态和分布以及细胞间连接接触的影响。结果发现，与繁殖季节的催乳素分泌细胞相比，非繁殖季节的催乳素分泌细胞体积更大，且含有更多的催乳素颗粒。与繁殖季节相比，非繁殖季节的FS细胞也更大，且形态发生了改变，即在繁殖季节，长细胞突起围绕着相邻分泌细胞簇。尽管在催乳素分泌细胞与FS细胞之间，或催乳素分泌细胞与促性腺细胞之间，连接数量没有显著变化，但催乳素分泌细胞之间以及FS细胞之间的黏着连接数量显著增加。这些发现表明催乳素分泌细胞和FS细胞的形态具有季节性可塑性，反映了催乳素分泌的变化。
