An immunogold investigation of the distribution of GABA and glycine in nerve terminals on the somata of spherical bushy cells in the anteroventral cochlear nucleus of guinea pig

Abstract

Spherical bushy neurons in the anteroventral cochlear nucleus receive glutamatergic primary terminals from the cochlear nerve and terminals of noncochlear (i.e. nonprimary) origin, many of which colocalize gamma-aminobutyric acid (GABA) and glycine. Here the relationship between GABA and glycine in these terminals has been investigated using postembedding immunogold labelling. A significant negative correlation was found between the density of terminal labelling for GABA and for glycine in four guinea pigs. Terminals could be divided into three categories, GABA-only, glycine-only, or colocalizing depending on whether they had a significantly higher labelling density for either amino acid than the primary terminals. The overall labelling density in all four animals was significantly greater for GABA in GABA-only terminals than colocalizing ones but similar for glycine in both. Within the terminals, the labelling density over synaptic vesicles, nonvesicular regions of cytoplasm and mitochondria was also investigated. No significant difference was detected in the labelling density of vesicles compared with nonvesicular regions for either amino acid. However, a significant difference was found between the overall labelling density over mitochondria and nonvesicular regions for both. There was also significantly more mitochondrial GABA labelling in GABA-only terminals compared to colocalizing terminals but mitochondrial glycine labelling was similar in glycine-only and colocalizing terminals. Thus the level of GABA is higher in single than in colocalizing terminals, particularly in the mitochondria, but similar for glycine in both. It is possible therefore that the presence of glycine affects the level of GABA in the nonprimary terminals but that the presence of GABA does not affect the level of glycine.

Transmission of phase-coupling accuracy from the auditory nerve to spherical bushy cells in the Mongolian gerbil

“…Since the analysis of our data confirmed earlier results by Caspary et al (1993Caspary et al ( , 1994, and Backoff et al (1997), who also found no differences between bicuculline and strychnine application in AVCN bushy cells, we subjected experiments with both drugs to an integrated analysis. This is in accordance with the immunocytochemical verification of GABA and glycine colocalization in afferent structures of the SBCs (Juiz et al, 1996;Mahendrasingam et al, 2004). To exclude the possibility that the observed effects were due to others than effects of the respective drugs, we performed control experiments (n ¼ 9), where the carrier was applied without the drug.…”

Developmental Shift of Inhibitory Transmitter Content at a Central Auditory Synapse

“…Anatomical studies in mature guinea pigs and rats have shown glycinergic, GABAergic and terminals colocalizing GABA and glycine on SBCs (Juiz et al, 1996; Mahendrasingam et al, 2000, 2004; Luján et al, 2008). Consistent with these results, the present data show putative glycinergic and GABAergic inputs on SBCs and, in addition, ~1/5 of pixels colocalizing markers for both transmitters at P25 and P60 (Figure 6).…”

Inhibition in the auditory brainstem enhances signal representation and regulates gain in complex acoustic environments

“…These SBCs receive suprathreshold excitatory input from auditory nerve fibers (ANF) via large axosomatic terminals, the endbulbs of Held (Brawer and Morest, 1975; Schwartz and Gulley, 1978; Ryugo and Sento, 1991; Nicol and Walmsley, 2002). In addition, inhibitory inputs on SBCs have been reported, which provide surprisingly slow acoustically evoked inhibition mediated by glycine and GABA (Wu and Oertel, 1986; Kolston et al, 1992; Juiz et al, 1996; Lim et al, 2000; Mahendrasingam et al, 2004; Xie and Manis, 2013), with glycine dominating (Nerlich et al, 2014b). …”