Mitochondrial ultrastructure and apoptotic protein expression in the vestibular nucleus complex following unilateral labyrinthectomy

Expression of glycine receptors and gephyrin in rat medial vestibular nuclei and flocculi following unilateral labyrinthectomy

The medial vestibular nucleus (MVN) and the cerebellar flocculus have been known to be the key areas involved in vestibular compensation (VC) following unilateral labyrinthectomy (UL). In this study, we examined the role of gephyrin and glycine receptor (GlyR) in VC using Sprague-Dawley rats, in an aim to gain deeper insight into the mechanisms responsible for VC. The expression of the α1 and β subunits of GlyR and gephyrin was immunohistochemically localized in rat MVN and flocculi. The mRNA and protein expression of GlyR (α1 and β subunits) and gephyrin was quantitatively determined by RT-qPCR and western blot analysis at 8 h, and at 1, 3 and 7 days following UL. It was found that in the ipsilateral MVN, the mRNA and protein expression of the β subunit of GlyR was significantly increased in comparison to the sham-operated (P<0.01) rats, and in comparison to the contralateral side (P<0.01) at 8 h following UL. In the ipsilateral flocculi, GlyR β protein expression was significantly elevated (P<0.01 for all), as compared to the sham-operated rats at 8 h, and at 1 and 3 days and to the contralateral side 8 h, 1 and 3 days following UL. No significant differences were observed in the mRNA and protein expression of GlyR α1 and gephyrin in the MVN or flocculi between the two sides (ipsilateral and contralateral) in the UL group, and between the sham-operated group and the UL group at any time point. The findings of our study thus suggest that GlyR plays a major role in the recovery of the resting discharge of the deafferented MVN neurons in the central vestibular system.

The changes in mGluR2 and mGluR7 expression in rat medial vestibular nucleus and flocculus following unilateral labyrinthectomy

It is known that the medial vestibular nucleus (MVN) and the cerebellar flocculus are the key areas, which contribute to the behavioral recovery ("vestibular compensation") after unilateral labyrinthectomy (UL). In these areas, how the genetic activities of the metabotropic glutamate receptors mGluR2 and mGluR7 performance after UL is unknown. With the means of quantitative real-time PCR, Western blotting, and immunohistochemistry, we analyzed the expression of mGluR2 and mGluR7 in the bilateral MVN and the flocculus of rats in different stages after UL (the 1st, 3rd, and 7th day). Our results show that in the MVN, the mRNA, and protein expressions of mGluR7 were ipsilaterally decreased at the 1st day following UL. However, in the MVN, no change was observed in the mRNA and protein expressions of mGluR2. On the other hand, the mRNA and protein expression of mGluR2 were enhanced in the ipsilateral flocculus at the 1st day following UL, while in the flocculus no change was shown in mGluR7 mRNA and protein expressions. Our results suggest that mGluR2 and mGluR7 may contribute to the early rebalancing of spontaneous resting activity in the MVN.

Postnatal expression of TrkB receptor in rat vestibular nuclear neurons responsive to horizontal and vertical linear accelerations

We examined the maturation expression profile of tyrosine kinase B (TrkB) receptor in rat vestibular nuclear neurons that were activated by sinusoidal linear acceleration along the horizontal or vertical axis. The otolithic origin of Fos expression in these neurons was confirmed with labyrinthectomized controls and normal controls, which showed only sporadically scattered Fos-labeled neurons in the vestibular nucleus. In P4-6 test rats, no Fos-labeled neurons were found in the vestibular nucleus, but the medial and spinal vestibular neurons showed weak immunoreactivity for TrkB. The intensity of TrkB immunoreactivity in vestibular nuclear neurons progressively increased in the second postnatal week but remained low in adults. From P7 onward, TrkB-expressing neurons responded to horizontal or vertical otolithic stimulation with Fos expression. The number of Fos-labeled vestibular nuclear neurons expressing TrkB increased with age, from 13-43% in P7 rats to 85-90% in adult rats. Our results therefore suggest that TrkB/neurotrophin signaling plays a dominant role in modulating vestibular nuclear neurons for the coding of gravity-related horizontal head movements and for the regulation of vestibular-related behavior during postnatal development.