N-methyl-D-aspartate receptors are present in vagal afferents and their dendritic targets in the nucleus tractus solitarius

N-Methyl-D-aspartate receptors are present in the nodose ganglion, which co ntains the cell bodies of vagal afferents, and in the nucleus tractus solit arius, where these afferent fibers terminate. This suggests that N-methyl-D -aspartate receptors are located presynaptically on visceral vagal afferent s and/or their target neurons in the nucleus tractus solitarius. To lest th is hypothesis, we combined anterograde transport of biotinylated dextran am ine, following injections into the left nodose ganglion, with electron micr oscopic immunogold labeling of antipeptide antiserum against the R1 subunit of the N-methyl-D-aspartate receptor in the nucleus tractus solitarius of rat brain. Within the medial nucleus tractus solitarius, the N-methyl-D-asp artate receptor R1 immunoreactivity was seen in dendrites (39% of 639 profi les), axons and axon terminals (41%), and a few neuronal perikarya and glia . Many vagal afferent axons and terminals (40% of 468 profiles) contained N -methyl-D-aspartate receptor R1 immunogold labeling. In addition, 42% of th e dendrites contacted by vagal afferent terminals (n = 206) contained N-met hyl-D-aspartate receptor R1 immunoreactivity. In axons and dendrites, the g old particles were occasionally seen within asymmetric postsynaptic junctio ns or at non synaptic sites on the plasma membrane. More commonly, however, N-methyl-D-aspartate receptor R1 labeling was seen on membranes of vesicul ar cytoplasmic organelles, suggesting that there is abundant N-methyl-D-asp artate receptor protein available for activity-dependent mobilization to th e plasmalemma. Since many vagal afferents are glutamatergic, our results implicate N-methy l-D-aspartate receptors in autoregulation of the presynaptic release and po stsynaptic responses to glutamate at the level of the first central synapse in the nucleus tractus solitarius. (C) 1999 IBRO. Published by Elsevier Sc ience Ltd.