Altered glycinergic synaptic activities in guinea pig brain stem auditory nuclei after unilateral cochlear ablation

This paper reviews efforts to determine if a unilateral hearing loss altere d inhibitory glycinergic synapses in the cochlear nucleus (CN) and the supe rior olive. In young adult guinea pigs, 2-147 days after unilateral cochlea r ablation, we quantified the electrically evoked release and the high-affi nity uptake of [C-14]glycine as measures of transmitter release from glycin ergic presynaptic endings and glycine removal from extracellular spaces. Th e specific binding of [H-3]strychnine was quantified to measure synaptic gl ycine receptor activity and/or expression. Three types of post-lesion chang e were observed. First, several tissues exhibited changes consistent with a persistent deficiency in glycinergic inhibitory transmission. Deficient bi nding prevailed on the ablated side in the anterior and caudal anteroventra l CN, the posteroventral CN and the lateral superior olive (LSO), while gly cine release was near normal and uptake was elevated (except in the LSO). H owever, deficient release prevailed in the dorsal CN, bilaterally, and was accompanied by elevated uptake. Second, the LSO on the intact side exhibite d changes consistent with strengthened glycinergic inhibition, as binding w as elevated while release and uptake were near normal. Third, several tissu es exhibited various transient changes in activity. These types of post-les ion change might contribute to altered auditory functions, which often acco mpany hearing loss. (C) 2000 Elsevier Science B.V. All rights reserved.