SOME FOREBRAIN CONNECTIONS OF THE GUSTATORY SYSTEM IN THE GOLDFISH CARASSIUS-AURATUS VISUALIZED BY SEPARATE DSI APPLICATION TO THE HYPOTHALAMIC INFERIOR-LOBE AND THE TORUS LATERALIS

The neuroanatomical connections of the diencephalic torus lateralis an d inferior lobe of the goldfish (Carassius auratus) were studied by re trograde and anterograde labeling with the carbocyanine dye DiI. Both structures have afferents originating in the central zone of the dorsa l telencephalic area as well as in the supracommissural nucleus of the ventral telencephalic area, and in the secondary gustatory, tertiary gustatory, and posterior thalamic nuclei. Both structures investigated have efferents to the tertiary gustatory and posterior thalamic nucle i, as well as to the dorsal hypothalamus (dorsal hypothalamic neuropil ) and superior reticular formation. The torus lateralis receives addit ional afferents from the secondary general visceral nucleus and, spars ely, from the dorsal tegmental nucleus. The inferior lobe receives add itional afferents from the medial zone of the dorsal telencephalic are a: as well as from the suprachiasmatic, posterior pretectal, central p osterior thalamic, caudal preglomerular, two tegmental nuclei (T1 and T2), corpus mamillare, and, sparsely, from the cerebellar valvula. The inferior lobe has additional efferents to the dorsal and ventral thal amus and subglomerular nucleus. The lateral torus and inferior lube ar e also mutually interconnected. The lateral torus and inferior lobe ma p topographically onto the vagal-related (intraoral) or onto the facia l-related (extraoral) portions, respectively, of both the secondary an d tertiary gustatory nuclei. Because the posterior thalamic nucleus is reciprocally connected with the lateral torus and inferior lobe and i s further known to project in turn to the area doralis telencephali, i t Likely represents a quaternary gustatory projection nucleus to the t elencephalon in cyprinids. Whereas the lateral torus seems to be exclu sively involved with gustatory and general visceral systems, the infer ior lobe has inputs from additional sensory (e.g., octavolateralis, vi sual) systems, and, thus, likely represents a multisensory integration center. (C) 1998 Wiley-Liss, Inc.