Reduced Glutamate Binding in Rat Dorsal Vagal Complex After Nodose Ganglionectomy

Quantitative receptor autoradiography with L-[3H]glutamate was employed to examine the distribution and properties of glutamate binding sites in the rat brain 14 days after excision of the right nodose ganglion. Slide-mounted coronal sections of the brain showed reduced L-[3H]glutamate binding in the nucleus tractus solitarius/dorsal motor nucleus of the vagus in the ipsilateral relative to the sham-operated side. Densitometric and saturation analyses of binding data indicated a significant reduction in the density of glutamate binding sites (57% decrease relative to sham), while there was a significant increase in receptor affinity (40% greater than sham). Binding was unaltered in the inferior olivary complex. Glutamate receptors are likely to exist on synaptic nerve terminals of vagal afferent fibres within the nucleus tractus solitarius and on vagal preganglionic neurones within the dorsal motor nucleus of the vagus and/or their dendritic processes within the nucleus tractus solitarius. Additionally, our receptor autoradiographic studies provide evidence for L-glutamate being a transmitter of vagal afferent neurones.