Recio J, Pévet P, Masson-Pévet M
Neurobiologie des Fonctions Rythmiques et Saisonnières, Université Louis Pasteur, Strasbourg, France.
J Neuroendocrinol. 1998 Apr;10(4):303-8. doi: 10.1046/j.1365-2826.1998.00208.x.
The exposure of long day seasonal breeders to a short photoperiod (SP) induces both sexual quiescence and a decrease in pars tuberalis (PT) melatonin receptor density. Therefore, we studied the respective roles of melatonin and testosterone on the regulation of PT melatonin receptors in Syrian hamsters transferred from long photoperiod (LP) to SP. Compared with intact sexually active animals in LP, the density of melatonin receptors was not affected by the absence of melatonin after removal of the pineal gland from animals kept in either SP or LP. In contrast, the presence of a long melatonin peak in the blood which induces gonadal atrophy induced a significant decrease in binding capacity. The SP-induced decrease in PT melatonin receptor density was also observed in castrated animals showing that it was directly regulated by melatonin, independently of circulating testosterone concentrations. However, the absence of testosterone induced an increased binding in LP, while increasing blood testosterone concentration after implantation of one testosterone-filled silastic tube resulted in a decrease in binding both in LP-and in SP-animals. These results indicate that testosterone induces a photoperiod-independent decrease in PT melatonin receptor density. In summary, these results show that both melatonin and testosterone have negative regulatory effects on the density of PT melatonin receptors.
长日照季节性繁殖动物暴露于短光照周期（SP）会导致性静止以及结节部（PT）褪黑素受体密度降低。因此，我们研究了褪黑素和睾酮对从长光照周期（LP）转移至SP的叙利亚仓鼠PT褪黑素受体调节的各自作用。与处于LP的完整性活跃动物相比，从处于SP或LP的动物摘除松果体后，褪黑素受体密度不受褪黑素缺失的影响。相反，血液中诱导性腺萎缩的长时褪黑素峰值的出现导致结合能力显著下降。在去势动物中也观察到SP诱导的PT褪黑素受体密度降低，表明其直接受褪黑素调节，与循环睾酮浓度无关。然而，睾酮缺失导致LP中的结合增加，而在植入一根填充睾酮的硅橡胶管后增加血液睾酮浓度会导致LP和SP动物中的结合均减少。这些结果表明，睾酮诱导PT褪黑素受体密度出现与光照周期无关的降低。总之，这些结果表明褪黑素和睾酮对PT褪黑素受体密度均有负调节作用。
