Cellular Neurophysiology of the Rat Suprachiasmatic Nucleus: ElectricalProperties, Neurotransmission, Mechanisms of Synchronization

摘要

Early experiments included sharp-intracellular-electrode analyses of amino-acid-mediated synaptic transmission and intrinsic membrane properties, designed in part to reveal the degree to which SCN neurons are homogenous or heterogenous. This work showed that glutamate and GABA play critical roles in synaptic transmission in the SCN, and that SCN neurons are not homogenous in terms of their electrophysiological properties, although they could not be grouped into distinct neuron classes. Multiple-unit extracellular recordings showed synchronous bursts of action potentials in the SCN in low Ca2+ solutions containing amino-acid-receptor antagonists (demonstrated to block chemical synapses), thus suggesting that SCN neurons are capable of communicating through nonsynaptic mechanisms. Whole-cell patch-clamp data showed that SCN neurons have a novel delayed outward-rectifier K+ current and a transient K+ current (i.e., A-current), both of which are present in all SCN neurons. More recently, we have studied local synaptic circuits and GABA-mediated inhibition in the SCN. Using glutamate microapplication to selectively stimulate only SCN neurons, we have provided physiological evidence that SCN neurons are interconnected by inhibitory circuits.