Analysis of electrophysiological properties and transmissions in rat suprachiasmatic nucleus neurons

对体外培养的大鼠视交叉上核（SCN）脑切片神经元进行细胞外和细胞内记录。大多数SCN神经元（85%）表现出频率为2-10 Hz的自发动作电位放电。动作电位前有去极化前电位，超极化后有浅而短的尖峰。施加超极化直流电流或河豚毒素阻断自发动作电位。向SCN神经元注入持续时间为400 msec的去极化电流，可引起动作电位的强直性放电，但没有明显的调节作用。通过注入持续时间为200 msec的内向电流脉冲，超极化电紧张电位的膜电阻“凹陷”随时间和电压的变化而降低。电压-电流关系在负电位大于- 80mv时表现为向内整流。胞外Cs（2 mM）阻断了向内整流，Ba（200 mM）不阻断。SCN神经元在无ca溶液和Cd（500 muM）或Co（1 mM）阻断的超极化电流松弛时也表现出反弹的缓慢去极化反应。4-AP增强了慢去极化。Cd和Cs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、内向整流和电流是决定SCN神经元自发放电活动速率的重要因素。视交叉刺激可诱发SCN神经元的EPSP和IPSP。应用CNQX和APV可阻断EPSP，表明EPSP是由NMDA和非NMDA受体介导的。由于IPSP被双核碱阻断，GABA_A受体可能介导IPSP。这些结果表明，这些突触活动可能调节SCN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.