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T Ohgaki

Publications and source records attributed to T Ohgaki.

23 records · Page 2Linked to original sources
PubMed1987

Anatomy of physiologically identified eye-movement-related pause neurons in the cat: pontomedullary region.

Pause neurons (PNs) are inhibitory neurons close to the midline at the pontomedullary junction that fire tonically and then cease firing just prior to quick eye movements of visual or vestibular origin. Previous physiological evidence has shown that these neurons have a role of central importance in the generation of rapid eye movements in any direction and all major models of ocular motor control incorporate PNs as major elements. In this study in cats, we injected horseradish peroxidase intracellularly into somata or axons of physiologically identified PNs. After appropriate tissue preparation, cell body and axonal reconstructions were performed, with the aid of a camera lucida-equipped microscope. Fifty-three PNs were stained and reconstructed. These consisted of 17 cell bodies and dendrites and 36 axons. Seven of these included both cell bodies and axons. PN somas lay close to the midline in the nucleus raphe pontis and centralis superior, had extensive dendritic arborizations tending to arise from either pole of the elongated soma, and had axons which typically crossed the midline and bifurcated into long branches which extended rostrally and caudally, inferior to the medial longitudinal fasciculus. There were major terminal arborizations and boutons in areas just rostral and caudal to the abducens nucleus in areas where two types of premotor neurons, excitatory and inhibitory burst neurons, are concentrated. Many axosomatic contacts were noted. Other terminal arborizations and boutons were found close to the midline in a region rostral to abducens nucleus containing other neurons known to burst prior to quick eye movements, and in the nucleus reticularis gigantocellularis. Rostral stem axons could be traced to the level of the trochlear nucleus and inferior to the medial longitudinal fasciculus. The caudal stem axons could be traced parallel to the midline and inferior to the medial longitudinal fasciculus and as far caudally as the hypoglossal nucleus.

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PubMed1987

Tetrodotoxin-insensitive central depression by grayanotoxin-III in mice.

The effect of systemic administration of grayanotoxin (GTX)-III, a constituent in leaves of Pieris japonica D. Don with an ability to activate the voltage-sensitive sodium channels in excitable tissues, on general behaviors of animals was studied using Std-ddy mice. Intraperitoneal administration of the toxin (0.1-0.25 mg/kg b. wt.) resulted in a dose-dependent manner in a significant and reversible muscle relaxation, and a profound and long lasting (greater than or equal to 60 min) depression of locomotor activity. Pretreatment with GTX-III caused a profound potentiation of the duration of loss of righting reflex by pentobarbital with a concomitant delay of the onset of convulsive seizures by various convulsants such as strychnine, picrotoxin and pentetrazol. Neither tetrodotoxin (1-5 micrograms/kg, i.p.) nor Ro15-1788 (1-5 mg/kg, i.p.) prevented the GTX-III-induced suppression of locomotor activity. These results suggest that GTX-III may elicit a central depressant action in mice through a molecular mechanism other than activation of the voltage-sensitive sodium channels in the brain.

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PubMed1986

The morphology of single lateral vestibulospinal tract axons in the lower cervical spinal cord of the cat.

The intraspinal morphology of single lateral vestibulospinal tract (LVST) axons was investigated with the method of intra-axonal staining with horseradish peroxidase (HRP) and three-dimensional reconstruction of the axonal trajectory. Axons penetrated in the ventral funiculus at C5-C8 were identified as LVST axons by their monosynaptic responses to stimulation of the ipsilateral vestibular nerve and by their direct responses to stimulation of the ipsilateral Deiters' nucleus and LVST. Reconstructions were made from 34 well-stained LVST axons. Of these, 23 terminated in the brachial segments (C5-Th1) and the other 11 projected below Th2. These axons were traced over distances of 2.9-16.3 mm rostrocaudally. Within these lengths, one to seven axon collaterals (mean +/- S.D., 3.2 +/- 2.0, N = 19) were given off at right angles from the stem axons of LVST axons terminating in the brachial segments. The mean diameters of stem axons and primary collaterals were 4.5 microns and 1.6 micron, respectively. In the gray matter, collaterals ramified successively, pursued a delta-like path, and terminated mainly in laminae VII and VIII or lamina IX. The rostrocaudal extension of a single collateral was very restricted (mean +/- S.D., 760 +/- 220 microns, N = 16), in contrast to the extensive dorsoventral and mediolateral extent of the terminal arborization. There were usually gaps between adjacent collateral arborizations from the same stem axons, since the intercollateral distances ranged from 400 to 4,300 microns (mean = 1,490 microns). LVST axons terminating in brachial segments were divided into two groups--a medial group and a lateral group--on the basis of their projection sites in the transverse plane of the gray matter. The axons of the medial type had their main projection to laminae VII and VIII of Rexed, while those of the lateral type terminated in lamina IX. The terminal arborizations of the medial type LVST axons were mainly distributed over lamina VIII, where synaptic boutons appeared to make contact with proximal dendrites or somata of medium-sized and large neurons in the ventromedial nucleus and also in the medial portion of lamina VII adjacent to the central canal and dorsal to lamina VIII. Five out of 15 medial type axons had a bilateral projection. One or two collaterals of each of these axons crossed the midline through the anterior commissure and terminated in lamina VII or VIII. It was concluded that the contralateral projection was sparse.(ABSTRACT TRUNCATED AT 400 WORDS)

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