Tohru Ohgaki

Vestibular projections to the spinal cord: the morphology of single vestibulospinal axons.

The three-dimensional distribution of LVST and MVST axons was examined in the cat cervical spinal cord using an intra-axonal staining method. LVST and MVST axons were electrophysiologically identified by their responses to stimulation of the vestibular nucleus, bilateral vestibular primary afferents, the LVST and the MVST were stained with injection of HRP. The axonal trajectory was reconstructed from serial histological sections. LVST axons were found to have multiple axon collaterals in the cervical cord. The maximum number of the identified collaterals for one neuron was 7. These collaterals were observed in either LVST axons terminating at the cervical cord or those projecting below Th2. The rostro-caudal extension of terminals for each collateral was very restricted (mean = 760 μm) and much narrower than intercollateral intervals (mean = 1470 μm). In the gray matter, collaterals ramified successively, pursued a delta-like path, and terminated mainly in lamina VIII and in the medial part of lamina VII and many boutons made apparent contact with the cell bodies and the proximal dendrites of motoneurons in the ventromedial nucleus. Some terminals were also distributed to the ventrolateral part of lamina VII adjacent to lamina IX. One group of LVST axons projected to lamina IX in the lateral ventral horn and terminated on large neurons there, probably motoneurons of forelimb muscles. MVST axons had one to seven axon collaterals at C1–C3 within the range of the stained axon. Stem axons ran in the ventromedial funiculus and primary collaterals arose from them at right angles. Each collateral had a very nar-row rostrocaudal spread as in LVST axons. Terminals were distributed in laminae VIII and IX, including the ventromedial nucleus, the spinal accessory nucleus, and the commissural nucleus. Many terminals seemed to make contact with retrogradely labelled motoneurons of neck muscles. Both crossed and uncrossed MVST axons had these characteristics.

Comparison of the branching patterns of lateral and medial vestibulospinal tract axons in the cervical spinal cord

The morphology of single physiologically-identified lateral and medial vestibulospinal tract (LVST and MVST) axons was analysed, using intracellular staining with horseradish peroxidase (HRP) and three-dimensional reconstruction of axonal trajectories in the cat. Axons were penetrated in the cervical cord at C1-C8 with a microelectrode filled with 7% HRP. These axons were identified as vestibulospinal axons by their monosynaptic responses to stimulation of the vestibular nerve and further classified as either LVST or MVST axons by their responses to stimulation of the LVST and MVST. The stained axons could be traced over distances of 3-16 mm rostrocaudally. Within these lengths, both LVST and MVST axons were found to have multiple axon collaterals at different segments in the cervical cord. Up to seven collaterals were given off from the stems of MVST axons and LVST axons. The LVST axons included both neurones terminating at the cervical cord and those projecting further caudally to the thoracic or lumbar cord. Each collateral of these LVST axons, after entering into the gray matter, ramified successively in a delta-like fashion and terminated mainly in lamina VIII and in the medial part of lamina VII. Many boutons of both terminal and en passant types seemed to make contact with the cell bodies and proximal dendrites of neurones in the ventromedial nucleus (VM). Each collateral had a narrow rostrocaudal extension (0.2-1.6 mm, average 0.8 mm) in the gray matter in contrast to a much wider intercollateral interval (average 1.5 mm), so that there were gaps free from terminal boutons between adjacent collateral arborizations. The morphology of axon collaterals of MVST axons was very similar to that of LVST axons. The rostrocaudal extent of single axon collaterals was very restricted (0.3-2.1 mm) in contrast to the wide spread in a mediolateral or a dorsoventral direction. MVST axons had intensive projections to the upper cervical cord with multiple axon collaterals. One to seven collaterals of single MVST axons were found at C1-C3. Terminals of MVST axons were distributed in laminae VII, VIII and IX, including the VM, the nucleus spinalis n. accessorii (SA), and the commissural nucleus. Many terminals seemed to make contact with retrogradely-labelled motoneurones of neck muscles. Both axosomatic and axodendritic contacts were observed on motoneurones in various sizes. Some collaterals gave rise to terminal arborizations in both the VM and the SA. These results suggest that single LVST and MVST axons may control excitability of multiple dorsal axial muscles concurrently with their multiple axon collaterals at multisegmental levels.

Schwannoma of the posterior pharyngeal wall : a case report

Schwannoma arising in the posterior pharyngeal wall is rare. We report on a 60-year-old man who complained of discomfort in his pharynx, from whom a tumour was excised via an intraoral approach. No recurrence was seen after an 11-year follow-up. The nerve origin of the tumour is most likely to be the peripharyngeal plexus. This is the third such case reported.

Ethyl Loflazepate in the Treatment of Tinnitus

Ethyl loflazepate (Meilax®) was administered orally to 91 patients suffering from tinnitus, 58 with tinnitus and sensorineural hearing loss, 27 with tinnitus without hearing loss, and 6 with tinnitus accompanied by sudden deafness. The clinical severity of tinnitus was evaluated every two weeks in terms of loudness, continuity and annoyance. Medication was rate of as effective in 27.5%, moderately effevtive in 33%, slightly effective in 17.6% and not effective in 21.8% at the end of treatment. Effectiveness depend on the duration of treatment. Patients treated for a relatively long period showed greater clinical improvement. Two patients complained of sleepiness as a side effect. It was concluded that ethyl loflazepate is effective in reducing severity of tinnitus.