Abstract
The ascending projections to the lateral lemniscal nuclei and the inferior colliculus were investigated in the albino rat by using Fluoro-Gold, either alone or in combination with other retrograde tract tracers. Injections were made into the central nucleus of the inferior colliculus (ICC), the dorsal nucleus of the lateral lemniscus (DNLL), the intermediate nucleus of the lateral lemniscus (INLL), or the ventral nucleus of the lateral lemniscus (VNLL). The ICC receives both ipsilateral and contralateral projections from the DNLL and the lateral superior olive, major ipsilateral projections from the INLL, VNLL, medial superior olive, and superior paraolivary nucleus, and major contralateral projections from both dorsal and ventral cochlear nucleus. The DNLL receives a similar pattern of projections from the auditory lower brainstem nuclei. The INLL, in contrast, receives its major projections from the ipsilateral VNLL, lateral superior olive, medial superior olive, superior paraolivary nucleus, and medial nucleus of the trapezoid body, but does not receive a heavy projection from the contralateral lateral superior olive. It receives a major contralateral projection from the ventral cochlear nucleus, but a much lighter projection from the contralateral dorsal cochlear nucleus. The VNLL receives projections from the ipsilateral medial nucleus of the trapezoid body and the contralateral ventral cochlear nucleus, but does not receive projections from the medial or lateral superior olives, the superior paraolivary nucleus, or the dorsal cochlear nucleus. Thus, the three primary subdivisions of the rat's lateral lemniscus can be distinguished from each other on the basis of their distinctive projection patterns.