Strychnine blocks binaural inhibition in lateral superior olivary neurons

Abstract

The present study seeks to identify neurotransmitters mediating binaural inhibition in lateral superior olivary nucleus neurons. Neurons in this auditory structure receive inputs from both ears and are thought to code for localization of sound in space. Iontophoretic application of glycine during monaural stimulation was found to mimic the inhibition observed with binaural stimulation. Binaural inhibition was blocked by application of the glycine receptor antagonist, strychnine, as were the effects of iontophoretic application of glycine. The post-strychnine recovery time course for return of synaptically mediated binaural inhibition and recovery of the effects of iontophoretic glycine application were identical. Although the superior olivary complex (SOC) neurons displaying binaural inhibition could in some cases be inhibited by GABA, the binaural inhibition rarely was blocked by iontophoretic application of the GABA receptor antagonist, bicuculline. These findings suggest that glycine may be a neurotransmitter mediating binaural inhibition in certain SOC neurons and that the projection to the lateral superior olivary nucleus from the medial nucleus of the trapezoid body may be glycinergic.The superior olivary complex (SOC) is the first structure in the ascending auditory pathway to receive bilateral input (for review see Boudreau and Tsuchitani, 1970;Brugge and Geisler, 1978; Tsuchitani, 1978). The auditory nerve on each side projects from the cochlea to the cochlear nucleus on that side. Binaural neurons in the lateral superior olive (LSO) receive their predominant contralateral input from the opposite ventral cochlear nucleus (VCN) via a secure synapse in the ipsilateral medial nucleus of the trapezoid body (MNTB; see Fig. 1). Ipsilateral input comes directly from the homolateral VCN to the same neuron. Ultrastructural studies indicate the existence of at least three types of synaptic endings upon the neurons of the medial superior olive (MSO). The morphological characteristics of these endings suggest that some may be inhibitory but others may be excitatory (Clark, 1969;Perkins, 1973; Schwartz, 1980 trophysiological evidence indicates the existence of neurons in both the MS0 and LSO which are excited by inputs from one ear and inhibited by simultaneous stimulation of the opposite ear (Galambos et al., 1959; Brown, 1968, 1969;Guinan et al., 1972a, b; Tsuchitani, 1977 Tsuchitani, , 1978. The nature of the neurotransmitter mechanisms mediating this inhibition is not known, but the existence of binaural neurons within the SOC provides an opportunity to study the interaction between excitatory and inhibitory synaptic inputs by varying the acoustic stimulus to each ear. Recently, Zarbin et al. (1981), using autoradiographic evidence, demonstrated that strychnine, the specific glycine antagonist, displays significant receptor binding in the rat LSO and minimal binding in the rat MSO.The present study examines binaural inhibition and attempts to antagonize the synaptically mediated binaural inhibition b...

Glycine transporters are differentially expressed among CNS cells

“…Numerous studies have demonstrated both a-subunit receptor immunoreactivity (Aoki et al, 1988) and high binding of 'H-strychnine in the LSO (Sanes et al, 1987;Glendennig and Baker, 1988). Electrophysiological data have shown the presence of strychnine-sensitive synapses in the LSO (Moore and Caspary, 1983;Wu and Kelly, 1991). Other studies have shown a high-affinity uptake of ?H-glycine in terminals in the LSO (Schwartz, 1985).…”

Lateralization of Interimplant Timing and Level Differences in Children Who Use Bilateral Cochlear Implants

“…Two specialized nuclei of the SOC, the lateral superior olive (LSO) and the medial superior olive (MSO) are responsible for encoding ILDs and ITDs, respectively. The lateral superior olive (LSO), responsible for processing ILDs, consists of bipolar neurons excited by ipsilateral stimulation and inhibited by contralateral stimulation (Boudreau and Tsuchitani 1968;Moore 2000;Moore and Caspary 1983). The net result of excitatory and inhibitory inputs to each LSO encodes the range of ILDs, which can thus be further processed and interpreted at higher centres of the auditory system.…”

NMDA Currents Modulate the Synaptic Input–Output Functions of Neurons in the Dorsal Nucleus of the Lateral Lemniscus in Mongolian Gerbils

“…This fast, usually glycine-mediated inhibition is involved in coincidence detection (Brand et al, 2002;Pecka et al, 2008) and the temporally precise suppression of excitation (Tsuchitani and Boudreau, 1966;Boudreau and Tsuchitani, 1968;Moore and Caspary, 1983;Tollin and Yin, 2005). In the ascending pathways on the level of the dorsal nucleus of the lateral lemniscus (DNLL), GABAergic inputs suddenly generate an inhibition of a different time domain.…”