Takanori Saika

Localization of glycine receptor α1 subunit mRNA-containing neurons in the rat brain: An analysis using in situ hybridization histochemistry

The localization of glycine receptors in the rat brain was examined by means of in situ hybridization histochemistry using an oligonucleotide probe to the sequence of the alpha 1 subunit. Strongly- or moderately-labeled neurons were found in the cranial nuclei, sensory nuclei such as the spinal trigeminal nucleus, principal trigeminal nucleus, gracile and cuneate nuclei, dorsal and ventral cochlear nuclei, superior olivary nucleus, medial and lateral trapezoid nuclei, lateral lemniscus and vestibular nuclei, red nucleus, parabrachial area, cerebellar nuclei, dorsal tegmental nucleus, reticular formation and parafascicular nucleus. This study thus demonstrated the localization of neurons which are regulated by glycine via strychnine-sensitive glycine receptors in the rat brain.

Effects of nerve crush and transection on mRNA levels for nerve growth factor receptor in the rat facial motoneurons.

We found that the level of nerve growth factor receptor (NGF-R) mRNA in facial motoneurons was increased after both facial nerve crushing and transection by means of in situ hybridization histochemistry. The increased level of NGF-R mRNA was maintained for at least 8 weeks after facial nerve transection, while facial nerve crushing caused only a transient increase. Thus, expression of NGF-R mRNA paralleled the axonal regeneration process. In addition, the increase of NGF-R mRNA with crushing was more pronounced than with transection from the 3rd to the 14th day after the insult.

Changes in expression of peptides in rat facial motoneurons after facial nerve crushing and resection

In situ hybridization histochemistry was used to study changes in mRNAs coding neuropeptides such as alpha-calcitonin gene-related peptide (CGRP), beta-CGRP, cholecystokinin (CCK) and galanin, in rat facial motoneurons following axotomy of the facial nerve. In control rats, 38%, 55% and 7% of the facial motoneurons expressed alpha-CGRP, beta-CGRP and CCK mRNAs, respectively. No galanin mRNA-containing motoneurons were observed in these animals. The levels of mRNA for alpha-CGRP, CCK and galanin were increased while the beta-CGRP mRNA level was decreased after axotomy. The levels of mRNAs for these peptides returned to the control values by 2-4 weeks after nerve crush, whereas nerve resection had more prolonged effects. Within 3-4 weeks after injury, nerve resection had greater effects on beta-CGRP, CCK and galanin mRNAs than did nerve crush. Thus, there appear to be differences in the regulation of mRNA expression of these peptides in axotomized motoneurons.

Role of the flocculus in the development of vestibular compensation: immunohistochemical studies with retrograde tracing and flocculectomy using Fos expression as a marker in the rat brainstem

After unilateral labyrinthectomy in rats, Fos-like immunoreactive neurons appeared in the ipsilateral medial vestibular nucleus, contralateral prepositus hypoglossal nucleus and contralateral inferior olive beta subnucleus. and thereafter gradually disappeared in accordance with the development of vestibular compensation. This finding indicated that the activation of these nuclei is the initial event of vestibular compensation. In the present study, retrograde tracing experiments revealed that these Fos-like immunoreactive neurons project a proportion of their axons to the vestibulocerebellum (uvula-nodulus, flocculus). Before vestibular compensation was accomplished, right, left or bilateral flocculectomy was performed in right-labyrinthectomized rats. All these treatments caused reappearance of unilateral labyrinthectomy-induced behavioral deficits and Fos expression in the left medial vestibular nucleus and right prepositus hypoglossal nucleus. Since floccular efferents are GABAergic, these results indicate that the neurons in which Fos expression was detected by flocculectomy had been inhibited after unilateral labyrinthectomy by floccular Purkinje neurons and that disinhibition of these neurons induced by flocculectomy caused decompensation. Based on our present findings, we propose a hypothesis that the bilateral flocculus serves the restoration of balance between intervestibular nuclear activities to induce vestibular compensation after unilateral labyrinthectomy.

Effects of MK801 on Fos expression in the rat brainstem after unilateral labyrinthectomy

Unilateral labyrinthectomy (UL) causes ocular and postural asymmetries, which disappear over time in the processes of equilibrium recovery known as vestibular compensation. It has been reported that N-methyl-D-aspartate (NMDA) receptors are involved in vestibular compensation. In the present study, in order to elucidate the NMDA receptor-mediated neural circuit responsible for the development of vestibular compensation, we used Fos expression as a marker of neural activation and examined the effects of MK801, a specific antagonist of NMDA receptors, on UL-induced Fos expression in the rat brainstem. After UL, Fos-like immunoreactive (-LIR) neurons were observed in the ipsilateral medial vestibular nucleus (ipsi-MVe), the contralateral prepositus hypoglossal nucleus (contra-PrH) and the contralateral inferior olive beta subnucleus (contra-IOb). Fos-LIR neurons gradually disappeared in the processes of vestibular compensation. It is suggested that the activation of the ipsi-MVe, the contra-PrH and the contra-IOb neurons after UL are the initial event of vestibular compensation. Intraperitoneal injection of MK801 in the processes of vestibular compensation caused reappearance of UL-induced behavioral deficits. During the decompensation induced by MK801, Fos-LIR neurons appeared in the contra-MVe, the ipsi-PrH and the bilateral-IOB. It is suggested that the contra-MVe, the ipsi-PrH and the bilateral-IOb neurons are inhibited by glutamatergic synapses driving inhibitory neurons via NMDA receptors in the processes of vestibular compensation and that disinhibition of these nuclei induced by MK801 causes decompensation. However, MK801 caused neither Fos expression nor behavioral decompensation after vestibular compensation is accomplished. All these findings that the NMDA receptor-mediated inhibitory modulation in the central vestibular system plays an important role for the initial processes of the development of vestibular compensation.

Effects of Exposing the Opened Endolymphatic Sac to Large Doses of Steroids to Treat Intractable Meniere's Disease

To enhance the effect of treatment for intractable Menieres disease, we exposed the opened endolymphatic sac to high concentrations of steroids. This technique — endolymphatic sac drainage and steroid instillation surgery — involves the application of a mass of prednisolone followed by absorbable gelatin sponges soaked in a high concentration of dexamethasone into a sac lumen opened and expanded with a bundle of absorbable gelatin film. These sponges are also placed around the sac and coated with biochemical adhesive so that the medicine is slowly delivered into the sac over a prolonged period of time by means of a natural sustained-release vehicle. The short-term results (6 to 14 months) in 12 patients with Menieres disease, including those in stage IV, treated by the above techniques showed that definitive spells were completely controlled in all cases. Hearing was improved, and annoyance due to tinnitus was decreased in all cases except one.

Changes in Fos and Jun Expression in the Rat Brainstem in the Process of Vestibular Compensation

By means of immunohistochemical technique, we examined the changes in Fos and Jun expression after unilateral labyrinthectomy (UL) in the rat brainstem. We observed Fos-like immunoreactivity (-LIR) in the ipsilateral medial vestibular nucleus (ipsi-MVe), the contralateral prepositus hypoglossal nucleus (contra-PrH) and the contralateral inferior olive beta subnucleus (contra-IOb) 1 h after UL. Then, Fos expression in the contra-PrH and the contra-IOb disappeared 3 days after surgery. However, we still found the residual expression in the ipsi-MVe, which disappeared within 7 days. On the other hand, no Jun-LIR was detected in the vestibular or vestibular-related nuclei before or after the operation. Fos expression in the MVe, PrH and IOb was induced immediately after UL. Then, the Fos expression disappeared in accordance with the development of the vestibular compensation. These findings suggest that the transient Fos expression in the vestibular and vestibular related nuclei is a trigger of vestibular compensation.

Role of cholinergic mossy fibers in medial vestibular and prepositus hypoglossal nuclei in vestibular compensation

Several lines of evidence have suggested that acetylcholine is a possible neurotransmitter/neuromodulator involved in vestibular compensation. Further, the central vestibular system, oculo- and spino-motor neurons and peripheral vestibular efferents contain abundant cholinergic neurons. However, details of cholinergic effective sites during vestibular compensation remain to be clarified. In the present study, we selectively damaged rat vestibulo-floccular and vestibulo-uvulonodular cholinergic mossy fibers using ethylcholine mustard aziridinium ions. In these treated animals, unilateral labyrinthectomy caused more severe vestibulo-ocular deficits especially during the initial stage. From these findings we suggest that vestibulo-floccular and vestibulo-uvulonodular cholinergic mossy fibers contribute to the restoration of a balance between intervestibular nuclear activities for the induction of vestibular compensation during the initial stage.

Changes in preproenkephalin mRNA after unilateral and bilateral labyrinthectomy in the rat medial vestibular nucleus

We examined the expression of preproenkephalin (PPE) mRNA in the vestibular nuclei in rats using in situ hybridization histochemistry. In normal rats, PPE mRNA-positive cells were observed in the medial and spinal vestibular nuclei. After unilateral labyrinthectomy, PPE mRNA was increased in the medial vestibular nucleus on the operated side from the 1st through the 3rd day after the surgery. It is suggested that the changes in PPE mRNA level after labyrinthectomy are involved in vestibular compensation.

Effects of Pre-flocculectomy on Fos Expression and NMDA Receptor-mediated Neural Circuits in the Central Vestibular System after Unilateral Labyrinthectomy

In this study in order to elucidate the role of the flocculus in the whole process of vestibular compensation from the very early stage to the chronic stage, we first examined unilateral labyrinthectomy (UL)-induced spontaneous nystagmus (SN), a behavioral marker of vestibular compensation, and Fos expression, a marker of neural activity, in the vestibular brainstem in pre-unilateral flocculectomized (pre-UF) rats. UL in pre-UF rats caused more severe vestibulo-ocular deficits at the very early stage than it did in floccular-intact rats. Fos expression occurred in the medial vestibular nucleus contralateral to the UL side (contra-MVe) and the prepositus hypoglossal nucleus ipsilateral to the UL side (ipsi-PrH), whereas Fos expression was never seen after UL in floccular-intact rats. Therefore, these findings suggest the UL in pre-UF rats activates the contra-MVe and ipsi-PrH neurons and causes great imbalance between intervestibular nuclear activities, inducing more severe vestibular symptoms at the very early stage than those in floccular-intact rats. Next, we observed MK801 (a specific antagonist on the NMDA receptor)-induced SN in pre-UF rats at the chronic stage after UL. MK801 administration to pre-UL rats caused reappearance of SN even 14 days after UL, while administration to floccular-intact rats at a post-UL interval of 14 days never induced decompensation. Therefore, these findings suggest that the flocculus takes part in NMDA receptor-mediated neural circuits involved in vestibular compensation and modifies the neural interactions at the chronic stage after UL. Taken together, those results suggest that the flocculus plays important roles in the restoration of a balance between intervestibular nuclear activities, to reduce vestibular symptoms during the very early stage, and thereafter in the modification of NMDA receptor-mediated neural interactions in the central vestibular system at the chronic stage.In this study in order to elucidate the role of the flocculus in the whole process of vestibular compensation from the very early stage to the chronic stage, we first examined unilateral labyrinthectomy (UL)-induced spontaneous nystagmus (SN), a behavioral marker of vestibular compensation, and Fos expression, a marker of neural activity, in the vestibular brainstem in pre-unilateral flocculectomized (pre-UF) rats. UL in pre-UF rats caused more severe vestibulo-ocular deficits at the very early stage than it did in floccular-intact rats. Fos expression occurred in the medial vestibular nucleus contralateral to the UL side (contra-MVe) and the prepositus hypoglossal nucleus ipsilateral to the UL side (ipsi-PrH), whereas Fos expression was never seen after UL in floccular-intact rats. Therefore, these findings suggest the UL in pre-UF rats activates the contra-MVe and ipsi-PrH neurons and causes great imbalance between intervestibular nuclear activities, inducing more severe vestibular symptoms at the very early stage than those in floccular-intact rats. Next, we observed MK801 (a specific antagonist on the NMDA receptor)-induced SN in pre-UF rats at the chronic stage after UL. MK801 administration to pre-UL rats caused reappearance of SN even 14 days after UL, while administration to floccular-intact rats at a post-UL interval of 14 days never induced decompensation. Therefore, these findings suggest that the flocculus takes part in NMDA receptor-mediated neural circuits involved in vestibular compensation and modifies the neural interactions at the chronic stage after UL. Taken together, those results suggest that the flocculus plays important roles in the restoration of a balance between intervestibular nuclear activities, to reduce vestibular symptoms during the very early stage, and thereafter in the modification of NMDA receptor-mediated neural interactions in the central vestibular system at the chronic stage.