Skip to main page content
U.S. flag

An official website of the United States government

Dot gov

The .gov means it’s official.
Federal government websites often end in .gov or .mil. Before sharing sensitive information, make sure you’re on a federal government site.

Https

The site is secure.
The https:// ensures that you are connecting to the official website and that any information you provide is encrypted and transmitted securely.

Access keys NCBI Homepage MyNCBI Homepage Main Content Main Navigation
. 2014 Mar:309:44-54.
doi: 10.1016/j.heares.2013.11.005. Epub 2013 Nov 28.

Effects of cochlear ablation on amino acid levels in the rat cochlear nucleus and superior olive

Donald A Godfrey  1 , Yong-Ming Jin  2 , Xiaochen Liu  2 , Matthew A Godfrey  2
Affiliations

Effects of cochlear ablation on amino acid levels in the rat cochlear nucleus and superior olive

Donald A Godfrey et al. Hear Res. 2014 Mar.

Abstract

Amino acids have important roles in the chemistry of the auditory system, including communication among neurons. There is much evidence for glutamate as a neurotransmitter from auditory nerve fibers to cochlear nucleus neurons. Previous studies in rodents have examined effects of removal of auditory nerve input by cochlear ablation on levels, uptake and release of glutamate in cochlear nucleus subdivisions, as well as on glutamate receptors. Effects have also been reported on uptake and release of γ-aminobutyrate (GABA) and glycine, two other amino acids strongly implicated in cochlear nucleus synaptic transmission. We mapped the effects of cochlear ablation on the levels of amino acids, including glutamate, GABA, glycine, aspartate, glutamine, taurine, serine, threonine, and arginine, in microscopic subregions of the rat cochlear nucleus. Submicrogram-size samples microdissected from freeze-dried brainstem sections were assayed for amino acid levels by high performance liquid chromatography. After cochlear ablation, glutamate and aspartate levels decreased by 2 days in regions receiving relatively dense innervation from the auditory nerve, whereas the levels of most other amino acids increased. The results are consistent with a close association of glutamate and aspartate with auditory nerve fibers and of other amino acids with other neurons and glia in the cochlear nucleus. A consistent decrease of GABA level in the lateral superior olive could be consistent with a role in some lateral olivocochlear neurons. The results are compared with those obtained with the same methods for the rat vestibular nerve root and nuclei after vestibular ganglionectomy.

PubMed Disclaimer

Figures

Figure 1
Figure 1
Maps of microdissected freeze-dried transverse sections for lesioned-side (left side) and contralateral (right side) cochlear nuclei of a rat with 7 days survival after left cochlear ablation, with glutamate levels in mmol/kg dry weight plotted onto sample locations. Section numbers are presented at bottom; lower numbers are more caudal. In the maps, thick solid lines are outside borders of the freeze-dried sections, thick dashed lines are inside regional boundaries seen in the freeze-dried sections, dotted lines are regional boundaries traced from adjacent stained sections, and thin solid lines are tracings of the cuts made to isolate samples for assay. Scale bar at right shows dorsal (D), ventral (V), lateral (L), and medial (M) directions. Regional abbreviations are A, anteroventral cochlear nucleus (AVCN); G, granular region; I, interstitial nucleus (IN, or auditory nerve root); P, posteroventral cochlear nucleus (PVCN); d, f, and m, deep, fusiform soma, and molecular layers of dorsal cochlear nucleus.
Figure 2
Figure 2
Maps of the same microdissected freeze-dried transverse sections as in Figure 1, with taurine levels in mmol/kg dry weight plotted onto sample locations. Details and abbreviations as in Figure 1.
Figure 3
Figure 3
Comparisons between lesioned (left) and unlesioned (right) sides of amino acid levels in cochlear nucleus regions of rats with cochlear ablations and various survival times. Lesioned-side level minus unlesioned side level is expressed as percentage of the unlesioned-side (contralateral) level in each case. Standard errors and statistically significant differences are shown in Tables 2 and 3, and the significant differences between the two sides are repeated here: *p < 0.01, **p < 0.001. Some of the bars for IN (ANR) were allowed to go off scale in order to keep the same scale as for the other plots. Exact values can be calculated from the tables.
Figure 4
Figure 4
Plots of amino acid levels (mean ± SEM) vs. post-surgical survival time and lateral-to-medial position in the lateral superior olivary nucleus (LSO) on each side of one rat at 2 days, 7 days, 1 month (31 days), and 2 months (62 days) after left cochlear ablation surgery. For each LSO, 4 samples were dissected, so that n = 4 for each data point in the plots of the left column. Since the LSO was not dissected into lateral-to-medial sample locations for the left side of the rat with 1 month survival, the data points for the plots in the right column represent the averages for the rats with 2 days, 7 days, and 2 months survival (n = 3). The differences in GABA level between left (lesioned side) and right (contralateral) LSO were statistically significant at 7 days (P = 0.036), 1 month (P = 0.002), and 2 months (P = 0.014), and in positions 2 (second from lateralmost, P = 0.032) and 4 (medialmost, P = 0.025). For all samples combined (n = 16), the GABA level difference between left and right LSO was significant at P = 0.000008.
Figure 5
Figure 5
Comparison of effect of nerve transection on amino acid levels in the central portions (nerve roots) of the auditory and vestibular nerves. The data for the auditory nerve root (or interstitial nucleus) are from the present study, in which the nerve was transected by the cochlear ablation, while those for the vestibular nerve root are from a previous study (Godfrey et al., 2004b), in which the nerve was transected by vestibular ganglionectomy. Percentage differences between lesioned-side and contralateral nerve roots are compared at 1 week and 1 month after surgery, the two survival times that match between the studies. Because of the very low concentrations of GABA in the nerve roots, the sizeable percentage changes correspond to only small mmol/kg dry wt changes: −0.1 and +0.2 for ANR and −0.4 and +1.0 for VNR at 1 week and 1 month, respectively.
See this image and copyright information in PMC

Similar articles

See all similar articles

Cited by

See all "Cited by" articles

References

    1. Abbott SD, Hughes LF, Bauer CA, Salvi R, Caspary DM. Detection of glutamate decarboxylase isoforms in rat inferior colliculus following acoustic exposure. Neuroscience. 1999;93:1375–1381. - PubMed
    1. Albrecht J, Schousboe A. Taurine interaction with neurotransmitter receptors in the CNS: an update. Neurochem Res. 2005;30:1615–1621. - PubMed
    1. Aldskogius H, Kozlova EN. Central neuron-glial and glial-glial interactions following axon injury. Prog Neurobiol. 1998;55:1–26. - PubMed
    1. Alibardi L. Ultrastructural distribution of glycinergic and GABAergic neurons and axon terminals in the rat dorsal cochlear nucleus, with emphasis on granule cell areas. J Anat. 2003;203:31–56. - PMC - PubMed
    1. Apostolides PF, Trussell LO. Rapid, activity-independent turnover of vesicular transmitter content at a mixed glycine/GABA synapse. J Neurosci. 2013;33:4768–4781. - PMC - PubMed

Publication types