Yu G D, Rusak B, Piggins H D
Department of Biomedical Sciences, McMaster University, Hamilton, Ont., Canada.
Brain Res. 1993 Feb 5;602(2):191-9. doi: 10.1016/0006-8993(93)90682-d.
Rhythms of spontaneous firing rate and of responsiveness to pressure ejection of melatonin were recorded from neurons in the Syrian hamster suprachiasmatic nuclei (SCN) in a slice preparation. In animals taken from light-dark cycles (LD 14:10), SCN cells had high firing rates during the projected day and lower rates during the projected night. The proportion of melatonin-suppressed cells (35% overall) was also high during the day and fell during the night, while melatonin activated approximately 23% of cells at all phases. To assess the source of the melatonin-responsiveness rhythm, hamsters were exposed for approximately 48 h to constant illumination (LL) to suppress melatonin secretion. LL exposure before slice preparation altered both firing-rate and melatonin-responsiveness rhythms. Firing rates failed to show a morning peak and remained at low levels, with no indication of daily rhythmicity. Melatonin responsiveness also failed to show the usual rhythm and even tended to rise at night. Overall melatonin responsiveness rose after LL exposure so that 50% of cells were suppressed and 21% activated. LL exposure also increased the proportions of cells which showed regular baseline firing rates. Control studies indicated that pressure artifacts did not account for either suppression or activation by melatonin, while the composition of the saline vehicle appeared to be responsible for the activations recorded. The results indicate that brief LL exposure alters SCN sensitivity to melatonin and SCN rhythmicity in Syrian hamsters, perhaps as a result of the loss of the daily melatonin secretion rhythm. Physiological melatonin patterns may have important effects on the rodent circadian pacemaker.
在脑片标本中，记录了叙利亚仓鼠视交叉上核（SCN）神经元的自发放电频率节律以及对褪黑素压力喷射的反应性节律。在处于明暗周期（LD 14:10）的动物中，SCN细胞在预计的白天具有较高的放电频率，而在预计的夜间则较低。褪黑素抑制的细胞比例（总体为35%）在白天也较高，在夜间下降，而褪黑素在所有阶段激活约23%的细胞。为了评估褪黑素反应性节律的来源，将仓鼠暴露于持续光照（LL）约48小时以抑制褪黑素分泌。在制备脑片之前暴露于LL会改变放电频率和褪黑素反应性节律。放电频率未显示出早晨峰值并保持在低水平，没有每日节律的迹象。褪黑素反应性也未显示出通常的节律，甚至在夜间有上升趋势。总体而言，LL暴露后褪黑素反应性增加，因此50%的细胞被抑制，21%被激活。LL暴露还增加了显示规则基线放电频率的细胞比例。对照研究表明，压力伪迹不能解释褪黑素的抑制或激活作用，而生理盐水载体的成分似乎是记录到的激活作用的原因。结果表明，短暂的LL暴露会改变叙利亚仓鼠SCN对褪黑素的敏感性和SCN节律，这可能是由于每日褪黑素分泌节律丧失的结果。生理褪黑素模式可能对啮齿动物的昼夜节律起搏器有重要影响。
