Immunohistochemical detection of glutamate in rat vagal sensory neurons

Vagal primary afferent neurons have their cell bodies located in the nodose (inferior) and jugular (superior) vagal ganglia and send terminals into the nucleus tractus solitarii (NTS) which lies in the dorsomedial medulla. The presence of glutamate (Glu)-containing neurons in the rat nodose ganglion was investigated using immunohistochemistry. Glu-immunoreactivity on nodose sections was found in neuronal perikarya and nerve fibers, but not in non-neuronal elements such as Schwann cells and satellite cells. Both immunoreactive and non-immunoreactive ganglion cells were observed. The immunoreactive ganglion cells amounted to about 60% of the nodose population. No specific intraganglionic localization was observed for the non-immunoreactive cells. Immunoreactive perikarya were slightly smaller than the non-immunoreactive ones, but no relationship was found between size and staining intensities of immunoreactive neurons. The present data indicate that immunodetectable Glu is present in a large population of vagal afferent neurons. They therefore add to a growing body of evidence suggesting that Glu may be the main neurotransmitter released by vagal afferent terminals within the nucleus tractus solitarii.