褪黑素对大鼠下丘脑薄片视交叉上核神经元放电昼夜节律性的调制

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：⑴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ＣＴ１８－２０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

Modulation of circadian rhythm of discharges of suprachiasmatic nucleus neurons in rat hypothalamic slices by melatonin

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.