ANATOMY OF THE VENTRAL NUCLEUS OF THE LATERAL LEMNISCUS IN RATS - A NUCLEUS WITH A CONCENTRIC LAMINAR ORGANIZATION

The lateral lemniscus contains relay nuclei of the auditory pathway in which the neurons have been grouped into dorsal and ventral (VNLL) nu clei. The data about the cytoarchitecture of the VNLL are controversia l and no agreement exists concerning its tonotopical organization. In this paper, the cytoarchitecture of VNLL and the spatial distribution of its neurons projecting to the central nucleus of the inferior colli culus (CNIC) have been studied by using different tracers. Rats were i ontophoretically injected in the CNIC and grouped in three sets. Group 1 rats received large injections of biotinylated dextran amine (BDA). Group 2 animals received restricted single injections of BDA in the l ow-, medium-, or high-frequency regions of the CNIC. Group 3 rats were double injected, with horseradish peroxidase placed in the high-frequ ency region of the CNIC, and with biocytin in the low-frequency one. T he distribution of retrogradely labeled neurons in the ipsilateral VNL L was three-dimensionally reconstructed by use of a computer microscop e. The analysis of labeled neurons and Nissl material suggests that th e VNLL contains flat stellate neurons. Labeled flat stellate neurons a nd fibers are oriented in parallel and form fibrodendritic laminae. Th e projection from the VNLL to the CNIC is topographically organized: n eurons in peripheral laminae project to dorsolateral, low-frequency re gions of the CNIC, and those of central laminae project to ventromedia l, high-frequency regions. Each VNLL lamina forms a continuous ventrod orsal structure which resembles a helicoid. (C) 1996 Wiley-Liss, Inc.