Anatomy of the ventral nucleus of the lateral lemniscus in rats: A nucleus with a concentric laminar organization

Abstract

The lateral lemniscus contains relay nuclei of the auditory pathway in which the neurons have been grouped into dorsal and ventral (VNLL) nuclei. The data about the cytoarchitecture of the VNLL are controversial 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 colliculus (CNIC) have been studied by using different tracers. Rats were iontophoretically 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 low-, medium-, or high-frequency regions of the CNIC. Group 3 rats were double injected, with horseradish peroxidase placed in the high-frequency region of the CNIC, and with biocytin in the low-frequency one. The distribution of retrogradely labeled neurons in the ipsilateral VNLL was three-dimensionally reconstructed by use of a computer microscope. The analysis of labeled neurons and Nissl material suggests that the VNLL contains flat stellate neurons. Labeled flat stellate neurons and fibers are oriented in parallel and form fibrodendritic laminae. The projection from the VNLL to the CNIC is topographically organized: neurons in peripheral laminae project to dorsolateral, low-frequency regions of the CNIC, and those of central laminae project to ventromedial, high-frequency regions. Each VNLL lamina forms a continuous ventrodorsal structure which resembles a helicoid.

Auditory System

“…Remarkable progress has been achieved in understanding the anatomy and physiology of the rat nuclei of the lateral lemniscus (NLL) over the past two decades (Glenn and Kelly, 1992;Li and Kelly, 1992;Bajo et al, 1993Bajo et al, , 1998Merchán et al, 1994;Kelly, 1995b, c, 1996;Kidd and Kelly, 1996;Fu et al, 1996Fu et al, , 1997aFu et al, , 1997bMerchán and Berbel, 1996;Kelly et al, 1998aKelly et al, , 1998bKelly et al, , 2009Wu, 1998Wu, , 1999van Adel et al, 1999;Kelly and Kidd, 2000;Riquelme et al, 2001;Zhao and Wu, 2001;Irfan et al, 2005;Nayagam et al, 2005Nayagam et al, , 2006Kelly, 2006a, 2006b;Kelly et al, 2009). Unfortunately, however, the terminology used to refer to subdivisions of the NLL is problematic.…”

“…Unfortunately, however, the terminology used to refer to subdivisions of the NLL is problematic. Several cytoarchitectonic schemes have been proposed for different species by various authors (e.g., cat: Adams, 1979;Glendenning et al, 1981;Malmierca et al, 1998;Bajo et al, 1999;bat: Covey and Casseday, 1991;Covey 1993aCovey , 1993bYang et al, 1996;rat: Paxinos and Watson, 2014;Bajo et al, 1993;Caicedo and Herbert, 1993;Merchán et al, 1994;Merchán and Berbel, 1996;Riquelme et al, 2001;Nayagam et al, 2005Nayagam et al, , 2006. Most authors agree on the boundaries of the dorsal nucleus of the lateral lemniscus (DLL; Fig.…”

“…The rat VLL exhibit a variety of neuronal types with different shapes and sizes as seen in Nissl stained sections (Merchán and Berbel, 1996). These authors also demonstrate that the neurons form a partly continuous laminar structure and that VLL projections to the IC are topographically organized with respect to the sound frequency.…”

“…These authors also demonstrate that the neurons form a partly continuous laminar structure and that VLL projections to the IC are topographically organized with respect to the sound frequency. Thus, Merchán and Berbel (1996) concluded that the rat VLL is a single nucleus, composed of isofrequency laminae extending through the whole dorsoventral and rostrocaudal length of the complex. Although previous anatomical and physiological studies Guinan et al, 1972aGuinan et al, , 1972bWhitley and Henkel, 1984;Nayagam et al, 2005Nayagam et al, , 2006Kelly, 2006a, 2006b) argued against a tonotopic organization, it seems that the VLL may indeed be tonotopically organized (Merchán and Berbel, 1996;Malmierca et al, 1998;gerbil: Benson and Cant, 2008).…”

Anisotropic organization of the rat superior paraolivary nucleus

“…Therefore, the SPON joins many other auditory nuclei that have been characterized as possessing neurons with clearly flattened dendritic arbors. Such nuclei include the dorsal cochlear nucleus (Blackstad et al 1984;Berrebi and Mugnaini 1991), LSO (Cajal 1904;Scheibel and Scheibel 1974;Sanes et al 1990Sanes et al , 1992Vetter and Mugnaini 1992), MSO (Scheibel and Scheibel 1974), VLL (Merchán and Berbel 1996;Malmierca et al 1998), dorsal nucleus of the lateral lemniscus (Merchán et al 1994;Bajo et al 1999), and IC (Morest 1964;Faye-Lund and Osen 1985;Malmierca 1991;Oliver et al 1991;Malmierca et al 1993). …”