Characteristics of spontaneous and evoked GABAergic synaptic currents in cardiac vagal neurons in rats

Despite the importance of GABAergic input to cardiac vagal neurons the elec trophysiological properties and possible origins of this innervation have n ot yet been studied. Individual cardiac vagal neurons were identified by a retrograde fluorescent tracer and were studied in an in vitro slice prepara tion using patch-clamp electrophysiology. Cardiac vagal neurons received sp ontaneous GABAergic inhibitory post-synaptic currents (IPSCs) that were blo cked by the GABA, receptor antagonist bicuculline. The spontaneous presynap tic GABAergic input to cardiac vagal neurons in the nucleus ambiguus occurr ed at a significantly lower frequency than that recorded in cardiac vagal n eurons in the dorsal motor nucleus of the vagus. To identify a possible sou rce of the GABAergic innervation to cardiac vagal neurons the nucleus tract us solitarius was electrically stimulated. GABAergic synaptic currents in c ardiac vagal neurons, in both the dorsal motor nucleus of the vagus (DMNX) and the nucleus ambiguus (NA), were consistently evoked upon stimulation of the nucleus tractus solitarius and these responses were also blocked by bi cuculline. (C) 2001 Elsevier Science B.V. All rights reserved.