Analysis of electrophysiological properties and transmissions in rat suprachiasmatic nucleus neurons

在离体大鼠含视交叉上核（SCN）的脑片上进行细胞外和细胞内记录。大多数SCN神经元（85%）显示自发放电，频率为2-10 Hz.动作电位之前是去极化前电位，然后是浅而短的尖峰后超极化。自发动作电位被阻断超极化直流电流或河豚毒素。向SCN神经元注入持续时间为400毫秒的去极化电流，诱发动作电位的强直性放电，其中不包括明显的调节。通过注入持续时间为200毫秒的内向电流脉冲，产生了超极化电紧张性电位上的膜电阻“下垂”的时间和电压依赖性降低。电压-电流关系显示，在电位负大于-80 mV时，内向整流。内向整流被细胞外Cs（2 mM），但不是由Ba（200 μ M）。SCN神经元也表现出反弹缓慢去极化响应于超极化电流的松弛，在无钙溶液中被阻断，并通过应用镉（500 μ M）或钴（1 mM）。4-AP使慢去极化增强。镉和铯抑制去极化前电位，导致SCN神经元放电率下降。这些结果表明，低阈值钙峰、内向整流和A电流是决定SCN神经元自发放电活动速率的重要因素。刺激视交叉可引起SCN神经元EPSP和IPSP。应用CNQX和APV均阻断EPSP，表明EPSP由NMDA和非NMDA受体介导。由于荷包牡丹碱可阻断IPSP，因此GABA_A受体可能介导IPSP的发生。这些结果表明，这些突触活动可以调节SCN的自发活动的速率。

Extracellular and intracellular recordings were made from neurons in brain slice containing suprachiasmatic nucleus(SCN)of the rat, in vitro. A majority of SCN neurons(85 %)displayed a spontaneous firing of action potential with frequency of 2-10 Hz. The action potential was preceded by a depolarizing prepotential and followed by a shallow and short spike after-hyperpolarization. Spontaneous action potentials were blocked by applying hyperpolarizing DC current or by tetrodotoxin. Injection of depolarizing current with duration of 400 msec to SCN neurons evoked a tonic discharge of action potentials which comprised of no obvious accommodation. A time and voltage-dependent decrease in the membrane resistance 'sag' on hyperpolarizing electrotonic potential was produced by injection of inward current pulses with duration of 200 msec. Voltage-current relationship showed an inward rectification at potentials more negative than -80 mV. The inward rectification was blocked by extracellular Cs(2 mM)but not by Ba(200 muM). SCN neurons also displayed a rebound slow depolarization in response to relaxation of hyperpolarizing current that was blocked in Ca-free solution and by application of Cd(500 muM)or Co(1 mM). 4-AP enhanced the slow depolarization. Cd and Cs depressed the depolarizing pre-potential, resulting in a decreased rate of firings in SCN neurons. These results suggest that the low-threshold Ca-spike, the inward rectification and the Acurrent are important factors for determining the rate of spontaneous firing activity in SCN neurons. Stimulation of optic chiasma elicited EPSP and IPSP in SCN neurons. The EPSP is blocked by application of both CNQX and APV, suggesting that the EPSP is mediated by both NMDA and non-NMDA receptors. Since the IPSP was blocked by bicuculline, GABA_A receptors may mediate the IPSP. These results suggest that these synaptic activities may modulate the rate of spontaneous activity of the SCN.