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Am J Physiol Regul Integr Comp Physiol 292: R1907-R1915, 2007. First published January 11, 2007; doi:10.1152/ajpregu.00763.2006
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NEUROHUMORAL CONTROL OF CARDIOVASCULAR FUNCTION

Presynaptic {alpha}-adrenoceptors in median preoptic nucleus modulate inhibitory neurotransmission from subfornical organ and organum vasculosum lamina terminalis

Miloslav Kolaj and Leo P. Renaud

Neurosciences, Ottawa Health Research Institute and University of Ottawa, Ottawa, Ontario, Canada

Submitted 2 November 2006 ; accepted in final form 10 January 2007

The median preoptic nucleus (MnPO) in the lamina terminalis receives a prominent catecholaminergic innervation from the dorsomedial and ventrolateral medulla. The present investigation used whole cell patch-clamp recordings in rat brain slice preparations to evaluate the hypothesis that presynaptic adrenoceptors could modulate GABAergic inputs to MnPO neurons. Bath applications of norepinephrine (NE; 20–50 µM) induced a prolonged and reversible suppression of inhibitory postsynaptic currents (IPSCs) and reduced paired-pulse depression evoked by stimulation in the subfornical organ and organum vasculosum lamina terminalis. These events were not correlated with any observed changes in membrane conductance arising from NE activity at postsynaptic {alpha}1- or {alpha}2-adrenoceptors. Consistent with a role for presynaptic {alpha}2-adrenoceptors, responses were selectively mimicked by an {alpha}2-adrenoceptor agonist (UK-14304) and blockable with an {alpha}2-adrenoceptor antagonist (idazoxan). Although the {alpha}1-adrenoceptor agonist cirazoline and the {alpha}1-adrenoceptor antagonist prazosin were without effect on these evoked IPSCs, NE was noted to increase (via {alpha}1-adrenoceptors) or decrease (via {alpha}2-adrenoceptors) the frequency of spontaneous and tetrodotoxin-resistant miniature IPSCs. Collectively, these observations imply that both presynaptic and postsynaptic {alpha}1- and {alpha}2-adrenoceptors in MnPO are capable of selective modulation of rapid GABAA receptor-mediated inhibitory synaptic transmission along the lamina terminalis and therefore likely to exert a prominent influence in regulating cell excitability within the MnPO.

{alpha}1-adrenoceptors; {alpha}2-adrenoceptors; inhibitory postsynaptic currents


Address for reprint requests and other correspondence: L. P. Renaud, Neurosciences, Ottawa Health Research Institute, 725 Parkdale Ave., Ottawa, Ontario, Canada K1Y 4E9 (e-mail: lprenaud{at}ohri.ca)






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