Böckers T M, Bockmann J, Salem A, Niklowitz P, Lerchl A, Huppertz M, Wittkowski W, Kreutz M R
AG Molecular Neuroendocrinology, Institute of Anatomy, University of Münster, Germany.
Endocrinology. 1997 Oct;138(10):4101-8. doi: 10.1210/endo.138.10.5423.
When exposed to short-day conditions, hamsters and other long-day breeders undergo gonadal regression. With chronic exposure to short days, however, the animals become photorefractory and gonadal recrudescence occurs. The underlying mechanism for this insensitivity is still unknown. There is growing evidence, however, that specific cells of the pituitary pars tuberalis (PT) mediate these photoperiod/nonphotoperiod-dependent changes as a direct or indirect "Zeitgeber" for the endocrine system. We investigated messenger RNA (mRNA)/protein formation for several hypophyseal hormones (beta-TSH, beta-LH, PRL, common alpha-chain) in the pars distalis (PD) and PT of female Djungarian hamsters in long photoperiod (LP) and after 18, 28, and 38 weeks of short photoperiod (SP). As indicated by gonadal and body weight, the hamsters displayed gonadal regression after 18 and 28 weeks of SP; after 38 weeks of SP, all animals showed recrudescence. At 18 and 28 weeks of SP, only PRL mRNA and protein levels were significantly reduced in the PD and returned to LP values after 38 weeks of SP. The expression of hypothalamic tyrosine hydroxylase in the arcuate nucleus that was determined by immunocytochemistry and by in situ hybridization was also down-regulated in SP18 and SP28 with increasing levels at SP38. Urinary 6-sulfatoxymelatonin levels were elevated in SP with highest levels in the SP18 group. In the PT, beta-TSH mRNA and protein were not detectable in all SP groups compared with the moderate signal intensity in LP. The common alpha-chain mRNA and protein, however, which were also reduced in the animals of the SP18 group, were already elevated after 28 weeks of SP and nearly reached LP-levels after 38 weeks of SP. These results show that, in contrast to LH and TSH, PRL expression in the PD is a sensitive indicator for photoperiod dependent changes of the endocrine system and seems to be tyrosine hydroxylase independent. The increase of common alpha-chain expression in PT-specific cells depending upon duration of SP that precedes the hormonal changes in the PD leads us to speculate that PT-specific cells initiate spontaneous recrudescence via a PT-PD pathway.
当暴露于短日照条件下时，仓鼠和其他长日照繁殖动物会出现性腺退化。然而，长期暴露于短日照环境中，这些动物会变得光不应性，性腺会重新发育。这种不敏感性的潜在机制仍然未知。然而，越来越多的证据表明，垂体结节部（PT）的特定细胞作为内分泌系统的直接或间接“授时因子”介导这些光周期/非光周期依赖性变化。我们研究了长日照（LP）和短日照（SP）18周、28周及38周后雌性黑线仓鼠远侧部（PD）和PT中几种垂体激素（β-促甲状腺激素、β-促黄体生成素、催乳素、共同α链）的信使核糖核酸（mRNA）/蛋白质形成情况。如性腺和体重所示，仓鼠在短日照18周和28周后出现性腺退化；短日照38周后，所有动物均出现性腺重新发育。在短日照18周和28周时，远侧部中只有催乳素mRNA和蛋白质水平显著降低，短日照38周后恢复到长日照水平。通过免疫细胞化学和原位杂交测定的弓状核中下丘脑酪氨酸羟化酶的表达在短日照18周和28周时也下调，短日照38周时水平升高。短日照时尿中6-硫酸氧褪黑素水平升高，短日照18周组最高。在结节部，与长日照中的中等信号强度相比，所有短日照组均未检测到β-促甲状腺激素mRNA和蛋白质。然而，共同α链mRNA和蛋白质在短日照18周组动物中也减少，短日照28周后升高，短日照38周后几乎达到长日照水平。这些结果表明，与促黄体生成素和促甲状腺激素不同，远侧部中催乳素的表达是内分泌系统光周期依赖性变化的敏感指标，且似乎与酪氨酸羟化酶无关。结节部特异性细胞中共同α链表达随短日照持续时间增加，先于远侧部激素变化，这使我们推测结节部特异性细胞通过结节部-远侧部途径启动自发性性腺重新发育。
