EXCITATORY AMINO-ACID PROJECTIONS TO THE NUCLEUS OF THE SOLITARY TRACT IN THE RAT - A RETROGRADE TRANSPORT STUDY UTILIZING D-[H-3]ASPARTATE AND [H-3] GABA

Afferents to the nucleus tractus solitarius utilizing excitatory amino acid transmitters were described in rat brain by autoradiography following microinfusion and retrograde transport of D-[H-3]aspartate. Parallel experiments with the injection of [H-3]GABA were employed to establish the transmitter-selective nature of the retrograde labelling found with D-[H-3]aspartate, Following infusion of D-[H-3]aspartate, perikaryal labelling was heaviest in myencephalon, where at least 16 discrete nuclei were labelled. Heaviest labelling was localized bilaterally in the trigeminal nucleus with cells extending through its subdivisions and the entire rostrocaudal axis. Intense labelling was also obtained in the inferior olive, predominantly contralaterally, and non-perikaryal labelling noted. Vestibular, reticular and raphe nuclei contained heavily labelled perikarya. In cervical spinal cord, a moderate density of labelled cells was found in dorsal horn, adjoining the central canal (lamina X) and in the central cervical nucleus, along with appreciable labelling of processes and non-perikaryal labelling. The relative density of labelled perikarya in