Patterns of convergence in the central nucleus of the inferior colliculus of the Mongolian gerbil: organization of inputs from the superior olivary complex in the low frequency representation.

Nell B. Cant

doi:10.3389/fncir.2013.00029

Abstract

Projections to the inferior colliculus (IC) from the lateral and medial superior olivary nuclei (LSO and MSO) were studied in the gerbil (Meriones unguiculatus) with neuroanatomical tract-tracing methods. The terminal fields of projecting axons were labeled via anterograde transport of biotinylated dextran amine (BDA) and were localized on series of horizontal sections through the IC. In addition, to make the results easier to visualize in three dimensions and to facilitate comparisons among cases, the data were also reconstructed into the transverse plane. The results show that the terminal fields from the low frequency parts of the LSO and MSO are concentrated in a dorsal, lateral, and rostral area that is referred to as the “pars lateralis” of the central nucleus by analogy with the cat. This region also receives substantial input from both the contralateral and ipsilateral cochlear nuclei (Cant and Benson, 2008) and presumably plays a major role in processing binaural, low frequency information. The basic pattern of organization in the gerbil IC is similar to that of other rodents, although the low frequency part of the central nucleus in gerbils appears to be relatively greater than in the rat, consistent with differences in the audiograms of the two species.

Highlights

The inferior colliculus (IC) receives input from most of the auditory nuclei in the brainstem, as well as from a number of areas in the forebrain, including the auditory cortex
NOTE ON NOMENCLATURE In order to avoid excessive and potentially confusing use of terminology based on relative position, I have employed nomenclature used in descriptions of the IC of other species but not applied previously to the gerbil
This designation is adopted from the classic description of the cat IC (Morest and Oliver, 1984; Oliver and Morest, 1984). (This region probably corresponds to the part of the rat IC referred to as the “lemniscal zone” by Faye-Lund and Osen, 1985)

Summary

Introduction

The inferior colliculus (IC) receives input from most of the auditory nuclei in the brainstem, as well as from a number of areas in the forebrain, including the auditory cortex (reviewed, e.g., in Casseday et al, 2002; Malmierca, 2005). Similar to results in the cat, differential termination of inputs from some of the major afferent sources to the IC have been reported in rodents (e.g., projections from the cochlear nucleus: Oliver et al, 1999; Malmierca et al, 2005; Cant and Benson, 2008; projections from the superior olivary complex: Fathke and Gabriele, 2009; Saldaña et al, 2009; projections from the nuclei of the lateral lemniscus: Gabriele et al, 2000; commissural projections: Malmierca et al, 2009; projections from the auditory cortex: Saldaña et al, 1996; Bajo and Moore, 2005), but there are no detailed published descriptions of the terminal distribution of the inputs from the LSO and MSO, two brainstem nuclei that extract binaural cues important for sound localization and other perceptual processes. The extent to which the gerbil IC appears different from that of the cat or rat may be explained by a differential representation of specific frequency ranges in each species

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