Anatomical connections of auditory and lateral line areas of the dorsal telencephalon (Dm) in the osteoglossomorph teleost, Gnathonemus petersii

Abstract

Local field potentials evoked either by auditory or by mechanosensory (water displacement) lateral line stimuli were recorded in sensory subregions of the telencephalic nucleus dorsalis pars medialis (Dm) in the weakly electric fish Gnathonemus petersii. The neural tracer Neurobiotin was injected into these two physiologically defined subregions. A reciprocal connection between the two subregions of Dm, as well as cell bodies and terminals in other telencephalic regions, whose distribution was somewhat different for the two injection types, were found. The course of labeled fibers outside the telencephalon was similar after injections in both Dm regions. Fibers were seen running through the lateral forebrain bundle (lfb) to the ventral surface area of the brain within the diencephalic preglomerular region (PGv). Within a narrow streak along the ventral side of the brain densely arranged cell bodies were labeled. The locations of labeled cells within PGv were indistinguishable after tracer was injected into either acoustical or lateral line areas of Dm. Only after injection into the mechanosensory Dm region labeled cell bodies were found in the anterior preglomerular nucleus (PGa), in addition. When crystals of the fluorescent tracer DiI were inserted in the ventral part of PGv, a path of labeled fibers similar to that after telencephalic injections was found. Labeled terminals, but no cell bodies, were located both in the acoustical and in the mechanosensory regions of Dm as well as in several other telencephalic areas. Even though sensory regions in Dm that process acoustical and mechanical stimuli are segregated and unimodal, they both receive input from neurons of PGv. The specificity of the mechanosensory region of Dm might originate from the additional input from PGa and from other endbrain areas.