Changes of amino acid concentrations in the rat vestibular nuclei after midline lesions.

Changes in concentrations of amino acids, especially GABA, glutamate, and aspartate, occur in vestibular nuclei after removal of cerebellar and labyrinth inputs. Here, we examined the effects of transecting midline-crossing connections between the two vestibular nuclear complexes, which especially include commissural connections. Three rats were euthanized at each of 2, 7, and 30 days after a midline cut at the level of the vestibular nuclei. Two sham-lesioned rats were prepared for surgery but no cut made. Samples of superior (SuVN), dorsal and ventral lateral (LVNd and LVNv), dorsal and ventral medial (MVNd and MVNv), and spinal vestibular nuclei (SpVN) were microdissected from freeze-dried coronal sections and assayed for amino acid concentrations. Reductions of GABA concentration occurred by 2 days and continued through 30 days after surgery in most regions. Glutamate and aspartate concentrations decreased by 2 days in LVN and MVN, then glutamate showed some recovery by 30 days. Glutamine and taurine concentrations increased in almost all regions. Glycine concentration decreased in MVN and LVNv. Our results support association of GABA, glutamate, aspartate, and to some extent glycine, with vestibular crossed connections. Comparisons to our previous studies suggest some complex lesion effects, especially in LVNd.