mRNAs coding for neurotransmitter receptors and voltage-gated sodium channels in the adult rabbit visual cortex after monocular deafferentiation

Modulation of GABA receptor subunits in rat facial motoneurons after axotomy

Facial nerve axotomy is a good model for studying neuronal plasticity and regeneration in the peripheral nervous system. In the present study, we investigated the effect of axotomy on the different subunits of GABA(A) and GABA(B) receptors of facial motoneurons. The facial nerve trunk was unilaterally sectioned and operated rats were sacrificed at 1, 3, 8, 30, and 60 days later. mRNAs coding for alpha1, beta2, and gamma2 of GABA(A) receptors and for GABA(1B) and GABA(B2) receptors were down-regulated by axotomy. This decrease began as soon as 1 or 3 days after axotomy, and the minimum was 8 days post-lesion; the mRNA levels remained lower than normal at day post-lesion 60. The abundance of mRNAs coding for the three other alpha2, beta1, and beta3 facial subunits of GABA(A) receptors and for the pre-synaptic GABA(B1A) subunit remained unchanged during the period 1-8 days post-lesion. Immunohistochemistry using specific antibodies against alpha1, gamma2 subunits of GABA(A) and against GABA(B2) subunits confirmed this down-regulation. Colchicine treatment and blockade of action potential by tetrodotoxin significantly decreased GABA(A)alpha1 immunoreactivity in the axotomized facial nucleus after 7 days. Finally, muscle destruction by cardiotoxin or facial palsy induced by botulinum toxin failed to change GABA(A)alpha1 subunit expression. Our data demonstrate that axotomy strongly reduced the amounts of alpha1, beta2, and gamma2 subunits of GABA(A) receptors and B(1B) and B(2) subunits of GABA(B) receptors in the axotomized facial motoneurons. The loss of GABA(A)alpha1 subunit was most probably induced by both the loss of trophic factors transported from the periphery and a positive injury signal. It also seems to be dependent on activity disruption.

An in situ hybridization and immunofluorescence study of GABAA and GABAB receptors in the vestibular nuclei of the intact and unilaterally labyrinthectomized rat

We investigated whether the production of the sixteen subunits of the GABA(A) receptors and of the different variants of GABA Breceptors are modulated in rat medial vestibular nuclei (MVN) following unilateral labyrinthectomy. Specific alpha1-6, beta1-3, gamma1-3 and delta GABA(A) and GABA(B) B1 and B2receptor radioactive oligonucleotides were used for in situ hybridization to probe sections of rat vestibular nuclei. Specific antibodies against alpha1, beta2, beta3 and gamma2 subunits of GABA(A) receptors and against GABA( B)receptors were also used to detect a potential protein expression modulation. No asymmetry was observed by autoradiography in the intact and deafferented MVN at any time (5 h to 8 days) following the lesion and for any of the oligonucleotide probes used. Also, no difference in the alpha1, beta2, beta3 and gamma2 of the GABA(A) and in the GABA(B) receptor immunohistochemical signal could be detected between the intact and deafferented vestibular nuclei at any time following the lesion. Our data suggest that GABA(A) and GABA Breceptor density changes most probably were not involved in the early stage of the vestibular compensation process, i.e., in the restoration of a normal resting discharge of the deafferented vestibular neurons and consequently in the recovery of a normal posture and eye position.

Modulation of the beta1-3 voltage-gated sodium channels in rat vestibular and facial nuclei after unilateral labyrinthectomy and facial nerve section: an in situ hybridization study

We investigated whether the production of the mRNAs for the auxiliary beta subunits of the Na channels are modulated in deafferented medial vestibular nucleus (MVN) and in axotomized facial motoneurons. No beta1-3 mRNAs modulation was detected at any time following unilateral labyrinthectomy in the deafferented and intact medial vestibular nucleus. In contrast, beta1 gene expression in the axotomized facial nucleus decreased compared to controls as soon as day post-lesion 3.

Modulation of the voltage-gated sodium- and calcium-dependent potassium channels in rat vestibular and facial nuclei after unilateral labyrinthectomy and facial nerve transsection: an in situ hybridization study

We investigated whether the expression in the vestibular and facial nuclei of the voltage-dependent Na alpha I and Na alpha III channels and of the Ca(2+)-activated K(+)-channel subunits, small-conductance (SK) 1, SK2 and SK3, is affected by unilateral inner-ear lesion including both labyrinthectomy and transsection of the facial nerve. Specific sodium (Na alpha I, Na alpha III) and potassium (SK1, SK2, SK3) radioactive oligonucleotides were used to probe sections of rat vestibular and facial nuclei by in situ hybridization methods. The signal was detected with films or by emulsion photography. Animals were killed at various times following the lesion: 1 day, 3 days, 8 days or 30 days. In normal adult animals, mRNAs for Na alpha I, and SK1, SK2, and SK3 channels were found in several brainstem regions including the lateral, medial, superior and inferior vestibular nuclei and the facial nuclei. In contrast, there was little Na alpha III subunit mRNA anywhere in the brainstem. Following unilateral inner ear lesion in rats, the medial vestibular nuclei were probed with Na alpha I, Na alpha III, SK1, SK2 and SK3 oligonucleotide probes: autoradiography indicated no difference between the two sides, at any of the times studied. Na alpha I and SK2 mRNAs were less abundant and Na alpha III, SK1 and SK3 mRNAs were more abundant in the axotomized facial nuclei motoneurons than in controls. Removal of vestibular input did not affect the abundance of the mRNAs for the sodium- or calcium-dependent potassium channels in the deafferented vestibular nuclei. There is thus no evidence that modulation of these conductances contributes to the recovery of a normal resting discharge of the deafferented vestibular neurons and consequently to the functional recovery of the postural and oculomotor deficits observed at the acute stage. However, facial axotomy induced a long-term modulation of both Na and SK conductances mRNAs in the facial motoneurons ipsilateral to the lesion. Presumably, retrograde injury factors resulting from axotomy were able to alter durably the membrane properties and thus the excitability of the facial motoneurons.