γ‐aminobutyric acid and glycine in the baboon cochlear nuclei: An immunocytochemical colocalization study with reference to interspecies differences in inhibitory systems

Abstract

Previous studies of the cochlear nuclei in cat, rat, and guinea pig have demonstrated neural structures that are enriched in the inhibitory neurotransmitter amino acids gamma-aminobutyric acid (GABA) and glycine. In these mammals, inhibitory terminals are widely distributed throughout the nuclear complex, but somata of inhibitory neurons are concentrated in the dorsal cochlear nucleus, in granule cell regions, and in the cap area. Because these are the subdivisions that undergo the most pronounced phylogenetic changes in primates, we wanted to see whether the inhibitory systems are influenced by changes in cytoarchitecture. Therefore, we applied light microscopic postembedding immunostaining and optical densitometry to the cochlear nuclei of an anthropoid primate, the Senegalese baboon (Papio anubis). Our results demonstrate that, in baboon 1) glycinergic neurons and axons in the ventral cochlear nucleus seem to form a commissural system similar to that of other mammals; 2) the tuberculoventral system appears to be unchanged in morphology but exhibits a higher level of colocalization of GABA with glycine; 3) there is a reduction of the granule/cartwheel cell system, which is reflected in lesser numbers of inhibitory cartwheel, Golgi, and molecular layer stellate cells; 4) the cap area is larger than in rodents and carnivores and contains many neurons that colocalize GABA and glycine; and 5) throughout the nuclear complex, a higher proportion of the inhibitory terminals colocalize GABA and glycine. We conclude that modulation of the ascending auditory pathway in baboon is likely to differ from that in rodents and cat.

Effects of sodium salicylate on spontaneous and evoked spike rate in the dorsal cochlear nucleus

“…Fusiform cells receive strong glycinergic inhibitory inputs from cartwheel cells (Backoff et al, 1997; Juiz et al, 1996; Kaltenbach et al, 2005; Kaltenbach et al, 2002; Moore et al, 1996; Mugnaini, 1985; Rubio and Juiz, 2004), and recent evidence indicates that salicylate can inhibit glycine receptors containing alpha1-subunits (Lu et al, 2009). Therefore, we speculated that salicylate might increase the firing rate of fusiform cells by suppressing IPSC.…”

Auditory System

“…3 and 4;Mugnaini et al, 1980;Wouterlood et al, 1984;Ohlrogge et al, 2001;Dunn et al, 2006;Diño and Mugnaini, 2008). The granule cell areas are so prominent in many species, like the rat, that they are considered by some to form a third CN division (for review, see Diño and Mugnaini, 2008), although its presence in cetacea and primates is debated (Osen and Jansen, 1965;Osen, 1979a, 1979b;Moore et al, 1996; but see Rubio et al, 2008). Because their axons converge on the molecular layer of the DC, the granule cells and their afferents are believed to form a functionally unique system within the CNC (Dunn et al, 1996;Oertel and Young, 2004) that is thought to improve auditory performance by integrating acoustic and proprioceptive information through unknown mechanism(s).…”

“…8). The relative GABA and glycine content of these cells varies between species (Moore et al, 1996). The dendritic arbors of these cells are flattened in parallel with the pyramidal cell basal dendrites in the isofrequency planes (cat: Osen, 1983).…”

Cochlear nucleus auditory prostheses

“…Also, there is evidence that inhibition of multipolar neurons (''Off center-frequency inhibition") can enhance the multipolar neurons' sensitivity to amplitude modulation (Frisina et al, 1990), and so damage to, or loss of the inhibitory neurons would reduce the multipolar cells' sensitivity to amplitude modulation. Virtually all of the GABA-ergic and glycine-ergic (inhibitory) neurons in the ventral cochlear nucleus are located in the small cell cap (Kolston et al, 1992;Moore et al, 1996), a structure that is especially prominent in humans (Moore and Osen, 1979).…”