GLYCINE IMMUNOREACTIVE PROJECTIONS FROM THE DORSAL TO THE ANTEROVENTRAL COCHLEAR NUCLEUS

The aim of the present study was to investigate whether projections from the dorsal cochlear nucleus (DCN) to the anteroventral cochlear nucleus (AVCN) use either of two inhibitory transmitters, glycine or GABA. Retrograde HRP labeling of DCN-to-AVCN projection neurons was combined with postembedding immunocytochemistry in the DCN of guinea pigs. Following injections of HRP in the anterior or posterior divisions of AVCN, large numbers of neurons were labeled in the DCN. All of these were located in the deep layer, except for a few granule cells. Nearly all (96%) of the projection neurons were immunoreactive for glycine and most had dendritic and somatic morphologies corresponding to those of elongate neurons (so-called 'corn' cells); only a few resembled small stellate neurons. Few (3%) retrogradely labeled neurons were immunoreactive for GABA. The results suggest that projections from the deep DCN to the AVCN are formed primarily by glycinergic elongate neurons. These projections could have a substantial inhibitory influence on the output of neurons in the AVCN.