Glutamate and GABA-mediated synaptic currents in neurons of the rat dorsal motor nucleus of the vagus.

We report the presence of excitatory and inhibitory spontaneous and evoked synaptic currents in the dorsal motor nucleus of the vagus (DMV) in the rat upon vagal and perivagal stimulation. Whole cell current-clamp recordings from anatomically identified DMV neurons in rat brain stem slices show that these neurons are capable of sustained slow-frequency action potential firing probably because of the presence of pacemaker current. Spontaneously occurring, tetrodotoxin-resistant miniature inhibitory and excitatory synaptic potentials were observed. Stimulation of the vagus mostly induced antidromic action potentials in DMV neurons. However, careful positioning of the stimulating electrode in the tissue surrounding the recording neuron, and sometimes in the vagus itself, was capable of evoking orthodromic-evoked mixed inhibitory-excitatory postsynaptic potentials, and eventually, action potentials. Whole cell voltage-clamp recordings of the synaptic currents corresponding to these synaptic potentials in the presence of pharmacological antagonists of the neurotransmitters gamma-aminobutyric acid (GABA), glutamate, and glycine receptor subtypes indicate that the inhibitory synaptic currents are mediated by GABA-activated Cl- channels, while the excitatory synaptic currents are due to activation of ionotropic glutamate receptors of the N-methyl-D-aspartic acid (NMDA) and non-NMDA subtypes.