持续光照或摘除松果腺对仓鼠视交叉上核神经元褪黑素敏感性的影响

Effects of constant illumination or pinealectomy on the sensitivity to melatonin of hamster suprachiasmatic nucleus neurons

为探讨视交叉上核 (SCN)神经元对褪黑素敏感性的昼夜节律改变的机制 ,先对仓鼠进行持续光照或摘除松果腺 ,然后制成下丘脑薄片 ,记录昼夜周期中 SCN神经元的自发单位放电 ,并观察其对褪黑素的反应。结果表明 ,取自正常光照动物的脑薄片 ,SCN对外源性褪黑素产生抑制反应的单位数量有昼多夜少的节律性。取自持续光照条件下或摘除松果腺动物的 SCN,对外源性褪黑素反应的昼夜节律性消失。持续光照条件下 ,起抑制反应的单位数量增加 ,引起反应的阈值无明显改变 ;在摘除松果腺后 ,起抑制反应的单位数量减少 ,引起反应的阈值升高。实验结果提示 ,SCN神经元对外源性褪黑素敏感性 ,与内源性褪黑素水平和褪黑素受体的适应性调制有关 ,还可能与松果腺和内源性褪黑素的其他神经生化作用有关。

To explore the mechanism of the circadian rhythm of melatonin sensitivity in the suprachiasmatic nucleus (SCN) neurons, the effects of melatonin on the spontaneous unit discharge of SCN neurons were studied in hypothalamic slices taken from pinealectomized hamsters or from those exposed to constant illumination (LL). Results indicated that the number of units recorded from slices taken from normal light dark cycle (LD) animals showed a circadian rhythm in their sensitivity to melatonin. The proportion of melatonin suppressed units was high during the day and fell during the night. This daily rhythmicity in melatonin responsiveness of SCN units disappeared either in the LL exposed or in the pinealectomized animals. The overall number of the melatonin suppressed units rose and no significant change in response threshold was found after LL exposure. After pinealectomy the number of melatonin suppressed units fell and the response threshold rose. The results suggested that the circadian rhythm in the sensitivity of SCN neurons to exogenous melatonin was dependent on both the level of endogenous melatonin and the availability of receptors for melatonin. Other neurochemical actions of melatonin and pineal gland may be also related to the sensitivity of SCN neurons. [