Effects of VPAC2 receptor activation on membrane excitability and GABAergic transmission in subparaventricular zone neurons targeted by suprachiasmatic nucleus.

作者:	M L H J Hermes, M Kolaj, P Doroshenko, E Coderre, L P Renaud
语言:	Eng.
日期:	2009-09-03
学报:	Journal of neurophysiology (0022-3077)
发行:	J Neurophysiol. 2009 Sep;102(3):1834-42
摘要:	The hypothalamic suprachiasmatic nucleus (SCN) harbors the master circadian pacemaker. SCN neurons produce the amino acid gamma-aminobutyric acid (GABA) and several peptide molecules for coordination and communication of their circadian rhythms. A subpopulation of SCN cells synthesizes vasoactive intestinal polypeptide (VIP) and provides a dense innervation of the subparaventricular zone (SPZ), an important CNS target of the circadian pacemaker. In this study, using patch-clamp recording techniques and rat brain slice preparations, the contribution of VIP to SCN efferent signaling to SPZ was evaluated by examining membrane responses of SPZ neurons to exogenous VIP receptor ligands. In approximately 50% of the SPZ neurons receiving monosynaptic GABAA receptor-mediated inputs from SCN, bath-applied VIP (0.5-1 microM) resulted in a membrane depolarization caused by tetrodotoxin-resistant inward currents reversing at approximately -23 mV. These data suggest the existence of postsynaptic receptors that activate a nonselective cationic conductance. In addition, a subset of SPZ neurons showed an increase in the amplitude of SCN-evoked GABAergic inhibitory postsynaptic currents (IPSCs) and a decrease in their paired-pulse ratios. This, together with an increase in frequency of spontaneous and miniature IPSCs, implies the presence of presynaptic receptors that facilitate GABA release from SCN and possibly other synaptic terminals. The effects occurred in separate neurons and could be mimicked by the selective VPAC2 receptor agonist BAY 55-9837 (0.2-0.5 microM) and partially blocked by the VIP receptor antagonist VIP(6-28) (5 microM). The results indicate that VIP acts via both post- and presynaptic VPAC2 receptors to differentially modulate SCN GABAergic signaling to distinct subpopulations of SPZ neurons.
版权:	Journal of neurophysiology Neurosciences, Ottawa Hospital Research Institute and University of Ottawa, 725 Parkdale Avenue, Ottawa, Ontario, Canada K1Y 4E9.
全文:	DOI - Journal of neurophysiology (DOI) EBSCO - HTML (需要捐款) HighWire Press - HTML (需要捐款)
科目:	Animals, Bicuculline, Biophysics, Electric Stimulation, GABA Antagonists, Inhibitory Postsynaptic Potentials, Male, Membrane Potentials, Neurons, Paraventricular Hypothalamic Nucleus, Patch-Clamp Techniques, Peptide Fragments, Rats, Rats, Wistar, Receptors, Vasoactive Intestinal Peptide, Type II, Suprachiasmatic Nucleus, Synaptic Transmission, Vasoactive Intestinal Peptide, gamma-Aminobutyric Acid