Visual, lateral line, and auditory ascending pathways to the dorsal telencephalic area through the rostrolateral region of the lateral preglomerular nucleus in cyprinids

Abstract

Fiber connections of the rostrolateral region of the lateral preglomerular nucleus (PGlr) were studied by tract-tracing methods in carp and goldfish. The PGlr receives fibers from the optic tectum, ventrolateral nucleus of semicircular torus, ventromedial thalamic nucleus, medial pretoral nucleus, anterior tuberal nucleus, subglomerular nucleus, and (unexpectedly) also from the retina. Dendritic morphology of tecto-preglomerular neurons suggests that they receive retinal inputs. The PGlr can be further subdivided into dorsal (PGlr-d) and ventral (PGlr-v) zones, both of which are composed of somata and neuropil layers. Retinal and tectal fibers terminate mostly in the neuropil layer of the PGlr-d with the retinal terminals concentrated medially and tectal terminals laterally. Lateral line toral fibers terminate mainly in a lateral portion and ventromedial thalamic fibers in a medial portion of the somata layer of the PGlr-d. Auditory fibers from the medial pretoral nucleus and anterior tuberal nucleus terminate in the PGlr-v. The central nucleus of the semicircular torus also projects sparse fibers to the PGlr-v. The PGlr projects to the lateral, central, and medial parts of the dorsal telencephalic area, and the latter telencephalic part sends descending fibers to the PGlr. Differential distribution patterns of PGlr-d and PGlr-v fibers are noted within the dorsal telencephalic parts, suggesting that different sensory modalities may be represented in distinct regions at least to a certain degree.