Ascending gustatory pathways to the telencephalon in goldfish

Abstract

Ascending pathways to the telencephalon from the secondary gustatory nucleus (SGN), preglomerular tertiary gustatory nucleus (pTGN), and medial preglomerular nucleus (PGm) were examined by tract-tracing experiments in goldfish Carassius auratus. Tracer injections to the SGN suggest the presence of direct ascending pathways to the supracommissural and the dorsal parts of the ventral telencephalic area, and the medial part of the dorsal telencephalic area (Dm), restricted to its ventral region. The SGN experiments also suggest projections to the pTGN and PGm, and several neuronal types in the primary gustatory centers were newly found to give rise to ascending fibers to the SGN. Injections to the pTGN suggest reciprocal connections of the nucleus with the dorsal region of the Dm (dDm). Injections to the PGm resulted in labeled cells in the dorsal part of the SGN, the secondary general visceral nucleus, and the posterior part of the dorsal telencephalic area, suggesting that this preglomerular nucleus receives gustatory, general visceral, and olfactory inputs. Fibers labeled from the PGm terminated in the central part of the dorsal telencephalic area and the dDm; the latter region contained many labeled somata. The terminal zone of PGm fibers in the dDm is located laterally adjacent to that from the pTGN. Injection experiments to the pTGN and PGm also suggest connections of these nuclei with the inferior lobar nuclei and torus lateralis. Based on the results of the present as well as recent studies, an updated map is provided that shows by and large distinct sensory representation within the goldfish dorsal telencephalic area.