Nelson D E, Takahashi J S
Department of Neurobiology and Physiology, Northwestern University, Evanston, IL 60208.
Brain Res. 1991 Jul 19;554(1-2):272-7. doi: 10.1016/0006-8993(91)90200-f.
Visual sensitivity for light suppression of pineal melatonin was measured in golden hamsters using 300 s stimuli of monochromatic light (503 nm) in constant darkness. Increasing stimulus irradiance caused a monotonic decrease in pineal-melatonin content. Irradiance greater than 3.5 X 10(10) photons cm-2.s-1 caused significant reductions of melatonin in the hamster pineal. Saturation of the response occurred above 10(11) photons cm-2.s-1 and melatonin levels were suppressed to approximately 7% of levels measured in unstimulated animals. Using a 4-parameter Naka-Rushton function to fit the data, the half-saturation constant for suppression of pineal melatonin was 1.3 x 10(10) photons cm-2.s-1. The sensitivity of the photic-entrainment pathway for circadian rhythms has also been measured in the hamster using identical stimulus parameters. Light suppression of pineal melatonin was 25 times (1.4 log units) more sensitive to irradiance than the phase-shifting response measured for the circadian rhythm of running-wheel activity (comparing the half-saturation constants for the two responses). Both of these responses, however, are much less sensitive to light than other visual responses measured behaviorally in the golden hamster.
在恒暗条件下，使用300秒的单色光（503纳米）刺激，测量金黄仓鼠松果体褪黑素对光抑制的视觉敏感性。刺激辐照度增加导致松果体褪黑素含量呈单调下降。辐照度大于3.5×10¹⁰光子·厘米⁻²·秒⁻¹会使仓鼠松果体中的褪黑素显著减少。在10¹¹光子·厘米⁻²·秒⁻¹以上出现反应饱和，褪黑素水平被抑制到未受刺激动物测量水平的约7%。使用四参数中纳-拉什顿函数拟合数据，抑制松果体褪黑素的半饱和常数为1.3×10¹⁰光子·厘米⁻²·秒⁻¹。还使用相同的刺激参数在仓鼠中测量了昼夜节律光调节途径的敏感性。松果体褪黑素的光抑制对辐照度的敏感性比为跑步轮活动昼夜节律测量的相移反应高25倍（1.4个对数单位）（比较两种反应的半饱和常数）。然而，这两种反应对光的敏感性都远低于在金黄仓鼠行为学上测量的其他视觉反应。
