AFFERENT AND EFFERENT CONNECTIONS OF THE DORSOCENTRAL TELENCEPHALON IN AN ELECTROSENSORY TELEOST, GYMNOTUS-CARAPO

Biotinylated dextran amine was injected unilaterally into dorsal regio ns of the telencephalon of the weakly electric fish Gymnotus carapo in order to study the afferent and efferent connections of specific dors al regions with ventral regions of the telencephalon and with other re gions of the central nervous system. Efferent pathways from the dorsol ateral area of the telencephalon project ipsilaterally to the anterior hypothalamic nucleus. the ventral thalamus and magnocellular tegmenta l nucleus, whose axons reach the spinal cord. Anterograde labeling sho wed that the central division of the dorsal telencephalon sends effere nt projections through the lateral forebrain bundle towards the ipsila teral lateral and medial preglomerular nucleus, the prerectal nucleus, the optic tectum and the dorsal torus semicircularis, regions that ar e all involved in the processing of electrosensory and/or multisensory information. In addition, when biotinylated dextran amine was injecte d into the dorsal torus semicircularis, retrogradely labeled neurons w ere observed in the dorsocentral area of the telencephalon. The dorsoc entral area is also a target of the extra-telencephalic afferents orig inating from rostral, lateral and medial regions of preglomerular comp lex. Within the telencephalon, neurons of many ventral subdivisions pr oject ipsilaterally to the dorsocentral area. The dorsocentral, dorsol ateral and dorsomedial areas are connected ipsilaterally and reciproca lly. The dorsocentral area is reciprocally connected with its contrala teral homologue through the anterior commissure.