Margraf R R, Lynch G R
Department of Biology, Wesleyan University, Middletown, Connecticut 06459.
Am J Physiol. 1993 Mar;264(3 Pt 2):R615-21. doi: 10.1152/ajpregu.1993.264.3.R615.
We investigated the effects of daily melatonin (MEL) injection on phase angle of entrainment, duration of wheel-running activity (alpha), and frequency of suprachiasmatic nuclei (SCN) neuronal discharge in the photo-nonresponsive phenotype of the Djungarian hamster, Phodopus sungorus. Photo-nonresponsiveness is characterized by an absence of physiological adjustments to short days (SD). With respect to wheel-running activity, photo-nonresponsive hamsters have a large negative phase angle of entrainment and a compressed alpha under SD. These hamsters also have a delayed nocturnal MEL pulse. These circadian differences are correlated with the daily profile of SCN neuronal activity. In the present experiments, daily MEL injections to photo-nonresponsive hamsters resulted in molt, gonadal regression, and expansion in alpha until entrainment to lights off. Vehicle-injected controls did not exhibit any of these responses. SCN neuronal activity patterns recorded from MEL-injected photo-nonresponders, but not vehicle-injected controls, resembled electrical activity profiles of photoresponsive hamsters. These results demonstrate that MEL induces "photoresponsiveness" in previously photo-nonresponsive hamsters, that MEL modifies circadian behavior to resemble that of photoresponders, and that MEL injections affect the circadian rhythm of SCN neuronal firing.
我们研究了每日注射褪黑素（MEL）对黑线毛足鼠（Phodopus sungorus）光无反应表型中同步化相角、转轮活动持续时间（α）以及视交叉上核（SCN）神经元放电频率的影响。光无反应的特征是对短日照（SD）缺乏生理调节。关于转轮活动，光无反应的仓鼠在短日照下具有较大的负同步化相角和压缩的α。这些仓鼠的夜间MEL脉冲也延迟。这些昼夜节律差异与SCN神经元活动的每日变化相关。在本实验中，每日给光无反应的仓鼠注射MEL导致脱毛、性腺退化，并且α扩大直至与熄灯同步。注射赋形剂的对照组未表现出任何这些反应。从注射MEL的光无反应者而非注射赋形剂的对照组记录到的SCN神经元活动模式类似于光反应仓鼠的电活动概况。这些结果表明，MEL在先前光无反应的仓鼠中诱导出“光反应性”，MEL改变昼夜节律行为使其类似于光反应者，并且注射MEL会影响SCN神经元放电的昼夜节律。
