【摘要】 先用持续光照和松果腺切除预处理大鼠 ,然后制成下丘脑薄片 ,记录其视交叉上核 (SCN)神经元的自发放电 ,观察其昼夜变化和褪黑素 (MEL)对它的影响。实验结果表明 :(1)在正常光照 (光照∶黑暗 =12∶12 )条件下 ,SCN神经元自发放电频率呈现昼高夜低的节律性。在昼夜时间 (CT) 6～ 8出现放电高峰 ,频率约为 8 3Hz ;在CT18～ 2 0出现低谷 ,频率约为 3 8Hz。松果腺切除后 ,SCN神经元自发放电的昼夜节律性基本保持 ,但在持续光照条件下 ,昼夜节律基本消失。 (2 )SCN神经元对MEL反应以抑制为主。在正常光照条件下 ,在白昼SCN神经元对MEL反应性较高 ,最大抑制率在CT8～ 10 ,约为 42 % ;在黑夜较低 ,最大抑制率在CT2 2～ 2 4,约为 2 6 %。在持续光照和松果腺切除条件下 ,SCN神经元都失去对MEL反应的昼夜节律性 ,且反应性增高。 (3)ML 1受体拮抗剂luzindole能阻断由MEL引起的SCN神经元自发放电抑制 ,而ML 2受体拮抗剂哌唑嗪却不能阻断。实验结果提示 ,松果腺作为大鼠昼夜节律组构的一个调整器 ,通过MEL作用于SCN中的高亲和性ML 1受体 ,在反应的两个时间窗口 (CT8～ 10和CT2 2～ 2 4)调节SCN的昼夜节律活动。更多还原

【Abstract】 Spontaneous firing of suprachiasmatic nucleus (SCN) neurons and the effect of melatonin (MEL) were examined in hypothalamic slices made from pinealectomized rats or from the rats exposed to constant light. The results are as follows. (1) Under normal light cycle (light∶dark=12∶12), SCN neurons displayed a circadian rhythm in spontaneous discharges. A peak about 8 3 Hz was presented at CT (circadian time) 6～8 and a trough about 3 8 Hz at CT18～20. The circadian rhythm persisted after pinealectomy, but disappeared after constant light exposure. (2) The response of SCN neurons to MEL was mainly inhibitory. Under normal light exposure, the inhibitory proportion was higher during the subjective day with the largest proportion of about 42% at CT8～10, and was lower during the subjective night with the largest proportion of about 26% at CT22～24. Under both constant light exposure and pinealectomy, the circadian rhythm of the response of SCN neurons to MEL disappeared. (3) The inhibitory effect of MEL on spontaneous discharges of SCN neurons was blocked by ML 1 receptor antagonist luzindole, but not by ML 2 receptor antagonist prazosin. The above results suggest that pineal gland, as a regulator of the organization of circadian rhythm, regulates the circadian rhythm of SCN neurons at two responsive time windows (CT8～10 and CT22～24) through high affinity ML 1 receptors in SCN.更多还原