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¹ Department of Biological Sciences, University of Warwick, Coventry CV4 7AL, UK² Neurosciences Program, Ottawa Health Research Institute and University of Ottawa, Ottawa, Ontario, Canada, K1Y 4E9

The role of GABA receptors in synaptic transmission to neonatal rat sympathetic preganglionic neurones (SPNs) was investigated utilizing whole-cell patch clamp recording techniques in longitudinal and transverse spinal cord slice preparations. In the presence of glutamate receptor antagonists (NBQX, 5 µM and D-APV, 10 µM), electrical stimulation of the ipsilateral or contralateral lateral funiculi (iLF and cLF, respectively) revealed monosynaptic inhibitory postsynaptic potentials (IPSPs) in 75% and 65% of SPNs, respectively. IPSPs were sensitive to bicuculline (10 µM) in all neurones tested and reversed polarity around -55 mV, the latter indicating mediation via chloride conductances. In three neurones IPSPs evoked by stimulation of the iLF (n= 1) or cLF (n= 2) were partly sensitive to strychnine (2 µM). The expression of postsynaptic GABA_A and GABA_B receptors were confirmed by the sensitivity of SPNs to agonists, GABA (2 mM), muscimol (10–100 µM) or baclofen (10–100 µM), in the presence of TTX, each of which produced membrane hyperpolarization in all SPNs tested. Muscimol-induced responses were sensitive to bicuculline (1–10 µM) and SR95531 (10 µM) and baclofen-induced responses were sensitive to 2-hydroxy-saclofen (100–200 µM) and CGP55845(200 nM). The GABA_C receptor agonist CACA (200 µM) was without significant effect on SPNs. These results suggest that SPNs possess postsynaptic GABA_A and GABA_B receptors and that subsets of SPNs receive bilateral GABAergic inputs which activate GABA_A receptors, coupled to a chloride conductance. At resting or holding potentials close to threshold either single or bursts (10–100 Hz) of IPSPs gave rise to a rebound excitation and action potential firing at the termination of the burst. This effect was mimicked by injection of small (10–20 pA) rectangular-wave current pulses, which revealed a time-dependent, Cs⁺-sensitive inward rectification and rebound excitation at the termination of the response to current injection. Synaptic activation of a rebound excitation mediated by a time-dependent inward rectification expressed intrinsically by SPNs may provide a novel mechanism enabling SPNs to be entrained to rhythms driven from the brainstem or higher centres.

(Received 23 September 2003; accepted after revision 9 December 2003; first published online 12 December 2003)
Corresponding author D. Spanswick: Department of Biological Sciences, University of Warwick, Coventry CV4 7AL, UK.  Email: d.c.spanswick{at}warwick.ac.uk

This article has been cited by other articles:

				L. Wang, E. Spary, J. Deuchars, and S. A. Deuchars Tonic GABAergic Inhibition of Sympathetic Preganglionic Neurons: A Novel Substrate for Sympathetic Control J. Neurosci., November 19, 2008; 28(47): 12445 - 12452. [Abstract] [Full Text] [PDF]