Submitted on November 2, 2006
Accepted on January 10, 2007
Presynaptic 
adrenoceptors in median preoptic nucleus modulate inhibitory neurotransmission from subfornical organ and organum vasculosum lamina terminalis
Miloslav Kolaj1 and Leo P. Renaud2*
1 Neuroscience, Ottawa Health Research Institute and University of Ottawa, Ottawa, Canada
2 Division of Neurology/Neurosciences, Ottawa Health Research Institute and University of Ottawa, Ottawa, Canada
* To whom correspondence should be addressed. E-mail: lprenaud{at}ohri.ca.
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 20-50µM) induced a prolonged and reversible suppression of inhibitory postsynaptic currents (IPSCs) and reduced paired pulse depression evoked by stimulation in the subfornical organ (SFO) and organum vasculosum lamina terminalis (OVLT). These events were not correlated with any observed changes in membrane conductance arising from NE activity at postsynaptic 
1 or 2 adrenoceptors. Consistent with a role for presynaptic 2 adrenoceptors, responses were selectively mimicked by an 2 adrenoceptor agonist (UK-14304) and blockable with an 2 adrenoceptor antagonist (idazoxan). While an 1 adrenoceptor agonist cirazoline or an 1 adrenoceptor antagonist prazosin was without effect on these evoked IPSCs, NE was noted to increase (via 1 adrenoceptors) or decrease (via 2 adrenoceptors) the frequency of spontaneous and tetrodotoxin-resistant miniature IPSCs. Collectively these observations imply that both presynaptic and postsynaptic 1 and 2 adrenoceptors in MnPO are capable of selective modulation of rapid GABA-A receptor mediated inhibitory synaptic transmission along the lamina terminalis, and therefore likely to exert a prominent influence in regulating cell excitability within the MnPO.
