Ascending auditory projections to the inferior colliculus in the adult gerbil, Meriones unguiculatus

Abstract

Ascending auditory projections to the inferiorcolliculus (1C) of the adult gerbil were studied using the retrograde transport of horseradish perpxi‐dase. Our results indicate that in gerbils. The ICreceives afferent projections from most brainstem auditory nuclei. A strong contralateral projection orig‐inates in the cochlenr nuclear complex (CN). A smaller but consistent pro‐jection from all three divisions of ipsilateral CN is also present. The medial superior olive (MSO), superior parolivary nucleus, and ventral nucleus of the lateral lemniscus all maintain ipsilateral projections to the IC. Bilateral projections arise from the lateral superior olive, lateral nucleus of the tra‐pezoid body, and dorsal nucleus of the lateral lemniscus. Previous investigations in other mammalian species provide conflicting data concerning the magnitude of a direct ipsilateral projection from CN to the IC. Our quantitative data indicate that the ipsilateral projection from CN in the gerbil is nearly one third as large as the projection from ipsilateral MSO. The projection from contralateral CN is six times larger than the MSO projection. The distribution of labeled cells across the rostrocaudal extent of MSO and the three divisions of the cochlear nuclear complex are presented.