UNSPECIFIED. (2003) Orexins induce increased excitability and synchronisation of rat sympathetic preganglionic neurones. JOURNAL OF PHYSIOLOGY-LONDON, 549 (3). pp. 809-821. ISSN 0022-3751

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Abstract

The neuropeptides orexin A and B are synthesised by perifornical and lateral hypothalamic (LH) neurones and exert a profound influence on autonomic sympathetic processes. LH neurones project to spinal areas containing sympathetic preganglionic neurones (SPNs) and therefore may directly modulate sympathetic output. In the present study we examined the possibility that orexinergic inputs from the LH influence SPN activity. Orexin-positive neurones in the LH were labelled with pseudorabies virus injected into the liver of parasympathetically denervated animals and orexin fibres were found adjacent to the soma and dendrites of SPNs. Orexin A or B (10-1000 nm) directly and reversibly depolarised SPNs in spinal cord slices. The response to orexin A was significantly reduced in the presence of the orexin receptor 1 (OX1R) antagonist SB334867A at concentrations of 1-10 mum. Single cell reverse transcriptase-polymerase chain reaction revealed expression of mRNA for both OX1R and OX2R in the majority of orexin-sensitive SPNs. The orexin-induced depolarisation involved activation of pertussis toxin-sensitive G-proteins and closure of a K+ conductance via a protein kinase A (PKA)-dependent pathway that did not require an increase in intracellular Ca2+. Orexins also induced biphasic subthreshold membrane potential oscillations and synchronised activity between pairs of electrically coupled SPNs. Coupling coefficients and estimated junctional conductances between SPNs were not altered indicating synchronisation is due to activation of previously silent coupled neurones rather than modulation of gap junctions. These findings are consistent with a direct excitation and synchronisation of SPNs by orexinergic neurones that in vivo could increase the frequency and coherence of sympathetic nerve discharges and mediate LH effects on sympathetic components of energy homeostasis and cardiovascular control.

Item Type:	Journal Article
Subjects:	R Medicine > RC Internal medicine > RC0321 Neuroscience. Biological psychiatry. Neuropsychiatry Q Science > QP Physiology
Journal or Publication Title:	JOURNAL OF PHYSIOLOGY-LONDON
Publisher:	CAMBRIDGE UNIV PRESS
ISSN:	0022-3751
Official Date:	15 June 2003
Volume:	549
Number:	3
Number of Pages:	13
Page Range:	pp. 809-821
Identification Number:	10.1113/jphysiol.2002.033290
Publication Status:	Published
URI:	http://wrap.warwick.ac.uk/id/eprint/9607

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