Endothelin-1 increases the neuronal activity and augments the responses to glutamate in the NTS

The aims of this study were to determine 1) whether endothelin (ET)-1 affects the neuronal activity of the NTS neurons, 2) whether specific ET receptor antagonists affect the neuronal activity of the NTS neurons, and 3) whether ET-1 or ET receptor antagonists modulate the responses of the nucleus of the solitary tract (NTS) neurons to l-glutamate (Glu). The single-unit discharge was extracellularly recorded with a fine electrode from medulla brain slice preparations of rats. ET-1 and Glu were iontophoretically applied to the recorded neuron. Both ET-1 and Glu increased the neuronal activity. The ET receptor antagonist BQ-123 attenuated the basal neuronal activity. ET-1 augmented the magnitude of the increases in the neuronal activity evoked by Glu, and these responses were antagonized by BQ-123. These studies suggest the following conclusions: 1) ET-1 increases the neuronal activity of the NTS neurons via ET receptors, 2) endogenous ET plays a controlling role of the neuronal activity of NTS neurons, and 3) ET-1 augments the responses evoked by Glu, believed to be the neurotransmitter from the solitary tract, via ET receptors. These results suggest that ET-1 facilitates synaptic transmission in the NTS.