gms | German Medical Science

The lateral nucleus of the trapezoid body (LNTB) in the brainstem receives excitatory input predominantly from the ipsilateral ventral cochlear nucleus and LNTB neurons send ipsilateral descending projections to the cochlear nucleus and cochlea as well as ascending projections to the medial and lateral superior olive and the inferor colliculus. The majority of LNTB neurons is immunoreactive for inhibitory neurotransmitters GABA and/or glycine and consequently provides inhibitory input to the projection targets.

To assess potential age dependent changes in LNTB a quantitative light microscopic analysis in frontal brainstem sections at the level of the facial nerve tract was performed. In 9 young (< 1 year) and 16 old (> 3 years) gerbils neighbouring sections immunostained with antibodies against GABA, glycine or Nissl stained were selected for the analysis.

We did not observe significant age dependent changes for the cross sectional area of LNTB (young: 0.069 ± 0.013 mm²; old: 0.061 ± 0.013 mm²), the number of GABA- (young: 20.8 ± 4.6, old: 22.3 ± 2.2) and glycine-immunoreactive (young: 23.8 ± 4.4, old: 26.3 ± 4.1) neurons or the total number of neurons (Nissl stained; young: 45.4 ± 10.0 old: 48.0 ± 7.1) that were present in a single section. However, we observed a highly significant age dependent reduction of soma size (Spearman rank correlation, N = 25, p < 0.001) for GABA- (young 174µm², old 138 µm²) as well as glycine-immunoreactive (young 159µm², old 142 µm²) LNTB neurons.

These results demonstrate neither an age dependent shrinkage of LNTB nor a cell loss. However, inhibitory LNTB neurons were significantly smaller in old as compared to young animals. The reduced soma size in old animals could reduce the availability of GABA and glycine in the projection targets of LNTB.

Supported by the DFG Str275/4-4.