Topographic organization of the dorsal nucleus of the lateral lemniscus in the cat

Abstract

The dorsal nucleus of the lateral lemniscus (DNLL) is an auditory structure of the brainstem. It plays an important role in binaural processing and sound localization and it provides the inferior colliculus with an inhibitory projection. The DNLL is a highly conserved auditory structure across mammals, but differences among species in its detailed organization have been reported. The main goal of this study was to analyze the topographic organization of the cat DNLL. Single, small iontophoretic injections of biotinylated dextran amine were made at different loci in the central nucleus of the inferior colliculus (CNIC). The distribution of the labeled structures in the ipsi‐ and contralateral DNLL was computer reconstructed in three dimensions. In individual sections, a band of labeling is seen in the DNLL on both sides. These two labeled bands occupy symmetric locations and are made of retrogradely labeled neurons with flattened dendritic arbors oriented parallel to each other. Moreover, the ipsilateral labeled band contains labeled terminal fibers parallel to the labeled dendrites. With three‐dimensional reconstructions, it becomes evident that the labeled band seen in each individual DNLL section represents a slice through a rostrocaudally oriented lamina. The shape, size, orientation, and location of this lamina change as the injection site is shifted along the tonotopic axis of the CNIC. An injection in the low‐frequency region of the CNIC, produces a lamina that resembles a flattened tube located in the dorsolateral corner of the DNLL. An injection in the high‐frequency region of the CNIC, by contrast, results in a lamina that is an elongated sheet located at the ventromedial surface of the DNLL. The laminae of the DNLL might constitute the structural basis for its tonotopical organization. Previous studies (Merchán MA, et al. 1994. J Comp Neurol 342:259–278) in conjunction with our current results suggest that the laminar organization in the DNLL might be common among mammals. J. Comp. Neurol. 407:349–366, 1999. © 1999 Wiley‐Liss, Inc.

Plasticity in the Development of Afferent Patterns in the Inferior Colliculus of the Rat after Unilateral Cochlear Ablation

“…Given the relative isolation of decussating DNLL fibers from other ascending inputs to the IC, the midline commissure was severed to ensure complete labeling of the projections of interest. Labeling in every case yielded detectable axonal labeling that spanned the entire frequency-axis of the central nucleus, as well as retrogradely labeled cells present throughout DNLL isofrequency contours (Tanaka et al, 1985;Merchán et al, 1994;Bajo et al, 1999;Saint-Marie et al, 1999). Importantly, examination of retrogradely filled DNLL cells under high magnification revealed no evidence of collaterals to the ipsilateral IC.…”

Auditory System

“…Although a concentric tonotopic model has been suggested on the basis of functional mapping studies with c-fos (Friauf, 1992) single unit recordings are inconclusive and did not show a tonotopic organization Kelly et al, 1998a). In the cat Shneiderman et al, 1988;Bajo et al, 1999) the tonotopic sequence differs slightly from the rodent model.…”

“…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.…”

A Discontinuous Tonotopic Organization in the Inferior Colliculus of the Rat

“…Tonotopic maps are found throughout the auditory system from cochlear nucleus to auditory cortex (Ryan et al, 1988;Kaltenbach and Lazor, 1991;Friauf, 1992;Spirou et al, 1993;Malmierca et al, 1998;Bajo et al, 1999;Doron et al, 2002). Some appear to be continuous, whereas others are stepwise.…”