Changes in the immunohistochemical localization of the glycine receptor in the superior olivary complex of adult circling mice

Glycine is a transmitter in the human and chimpanzee cochlear nuclei

Introduction

Auditory information is relayed from the cochlea via the eighth cranial nerve to the dorsal and ventral cochlear nuclei (DCN, VCN). The organization, neurochemistry and circuitry of the cochlear nuclei (CN) have been studied in many species. It is well-established that glycine is an inhibitory transmitter in the CN of rodents and cats, with glycinergic cells in the DCN and VCN. There are, however, major differences in the laminar and cellular organization of the DCN between humans (and other primates) and rodents and cats. We therefore asked whether there might also be differences in glycinergic neurotransmission in the CN.

Methods

We studied brainstem sections from humans, chimpanzees, and cats. We used antibodies to glycine receptors (GLYR) to identify neurons receiving glycinergic input, and antibodies to the neuronal glycine transporter (GLYT2) to immunolabel glycinergic axons and terminals. We also examined archival sections immunostained for calretinin (CR) and nonphosphorylated neurofilament protein (NPNFP) to try to locate the octopus cell area (OCA), a region in the VCN that rodents has minimal glycinergic input.

Results

In humans and chimpanzees we found widespread immunolabel for glycine receptors in DCN and in the posterior (PVCN) and anterior (AVCN) divisions of the VCN. We found a parallel distribution of GLYT2-immunolabeled fibers and puncta. The data also suggest that, as in rodents, a region containing octopus cells in cats, humans and chimpanzees has little glycinergic input.

Discussion

Our results show that glycine is a major transmitter in the human and chimpanzee CN, despite the species differences in DCN organization. The sources of the glycinergic input to the CN in humans and chimpanzees are not known.

Human Superior Olivary Nucleus Neuron Populations in Subjects With Normal Hearing and Presbycusis

INTRODUCTION

Normative data on superior olivary nucleus neuron counts derived from human specimens are sparse, and little is known about their coherence with structure and function of the cochlea. The purpose of this study was to quantify the neuron populations of the divisions of the superior olivary nucleus in human subjects with normal hearing and presbycusis and investigate potential relationships between these findings and histopathology in the cochlea and hearing phenotype Methods: Histopathologic examination of temporal bone and brainstem specimens from 13 subjects having normal hearing or presbycusis was undertaken. The following was determined for each: number and density of superior olivary nucleus and cochlear nucleus neurons, inner and outer hair cell counts, spiral ganglion cell counts, and pure tone audiometry.

RESULTS

The results demonstrate a significant relationship between cells within structures of the cochlear nucleus and the number of neurons of the medial superior olivary nucleus. No relationship between superior olivary nucleus neuron counts/density and cochlear histopathology or hearing phenotype was encountered.

CONCLUSION

Normative data for superior olivary nucleus neuron populations are further established in the data presented in this study that includes subjects with normal hearing and also presbycusis.