Meijer J H, Groos G A, Rusak B
Brain Res. 1986 Sep 10;382(1):109-18. doi: 10.1016/0006-8993(86)90117-4.
The hypothalamic suprachiasmatic nuclei (SCN) of mammals function as a pacemaker driving circadian rhythms. This pacemaker is entrained to the daily light-dark cycle in the environment via the retina and central retinal projections to the anterior hypothalamus. We carried out a comparative study of the visual properties of rat and hamster SCN neurons. Extracellular single cell activity was recorded in the SCN of urethane-anaesthetized animals. In both species, visual SCN neurons responded to retinal illumination with a sustained increase or a sustained decrease in electrical discharge. The majority (75%) of these cells were activated by light. In both the rat and the hamster SCN, visually responsive cells altered their discharge rate as a monotonic function of luminance. The intensity-response curve could be described by a Michaelis function with a small working range between threshold and saturation (2-3 log units) and a relatively high threshold. Intensity-response curves in both species were occasionally different for increasing as opposed to decreasing luminance. Thus, hysteresis effects of illumination may occur in the SCN. The spontaneous firing rates as well as the responsiveness of visual SCN cells were subject to marked variations between and within cells. The overall photic responsiveness of SCN neurons, however, indicated that they are specialized for luminance coding in the range of light intensities naturally occurring at dawn and dusk. This property makes these cells suitable to mediate photic entrainment of circadian rhythms as well as the measurement of photoperiod.
哺乳动物的下丘脑视交叉上核（SCN）起着驱动昼夜节律起搏器的作用。该起搏器通过视网膜以及视网膜至下丘脑前部的中央投射，与环境中的昼夜明暗周期同步。我们对大鼠和仓鼠SCN神经元的视觉特性进行了比较研究。在氨基甲酸乙酯麻醉的动物的SCN中记录细胞外单细胞活动。在这两个物种中，视觉SCN神经元对视网膜光照的反应是放电持续增加或持续减少。这些细胞中的大多数（75%）被光激活。在大鼠和仓鼠的SCN中，视觉反应细胞的放电率随亮度的单调函数而变化。强度-反应曲线可用米氏函数描述，在阈值和饱和值之间有一个较小的工作范围（2-3个对数单位）且阈值相对较高。两个物种的强度-反应曲线在亮度增加和减少时偶尔会有所不同。因此，SCN中可能会出现光照的滞后效应。视觉SCN细胞的自发放电率以及反应性在细胞之间和细胞内部都有显著变化。然而，SCN神经元的整体光反应性表明，它们专门用于编码黎明和黄昏自然出现的光强度范围内亮度。这一特性使这些细胞适合介导昼夜节律的光同步以及光周期的测量。
