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I Koizuka

Publications and source records attributed to I Koizuka.

44 records · Page 3Linked to original sources
PubMed1983

In vivo 31P NMR studies on experimental cerebral infarction.

Sequential metabolic changes in rat brain were monitored by in vivo measurements of 31P NMR spectra using a topical magnetic resonance (TMR) spectrometer, during the course of experimentally induced cerebral infarction and also during recovery produced by restoration of circulation. The experimental cerebral infarction was rendered by a slightly modified version of the method of Pulsinelli and Brierley (1979). The bilateral coagulation of the vertebral arteries at the level of alar foramina of the first cervical vertebra (preinfarction) did not show any change in NMR spectrum, but the subsequent bilateral ligation of internal carotid arteries produced a decrease in the peaks of ATP and phosphocreatine and a concomitant increase in the peak of inorganic phosphate within a few minutes. Intracellular pH, calculated from the chemical shift of inorganic phosphate, declined. These changes became maximal at approximately 30 min after the infarction. Reinstatement of blood flow to the cerebrum, produced by untying the ligature of internal carotid arteries, resulted in an immediate restoration of the peaks of ATP and phosphocreatine, which was followed by a reduction in the peak of inorganic phosphate within a few minutes. The spectrum recovered to its preinfarction pattern about 30 min after the restoration of the circulation. These experiments demonstrate that phosphorus compounds change very rapidly during infarction, and that these changes were reversible at least during a 30 min period.

Adenosine Triphosphate↗
PubMedDate not supplied

Vestibulo-ocular reflex in eccentric rotation in squirrel monkeys.

In addition to angular acceleration, eccentric rotation (ECR) imparts linear acceleration to the head positioned eccentric to the axis of rotation. Using ECR in squirrel monkeys, the effects of otolith organ stimulation by linear acceleration on vestibulo-ocular reflex (VOR) gain were investigated. With the animal's head facing away from the rotation axis, ECR significantly enhanced VOR gain over that seen in centric rotation (CR) at 1.0 Hz, but not at 0.5 Hz. However, no enhancement of VOR gain at 1.0 Hz was observed in eccentriclateral rotation when the animal faced tangentially. After bilateral ablation of the otolith organs (sacculectomy and utricular neurectomy), the ECR did not increase VOR gain, even at 1.0 Hz. In animals in which the lateral and posterior semicircular canals were plugged bilaterally, horizontal sinusoidal eye movements were induced by ECR at 1.0 Hz; no clear compensatory eye movement occurred during CR at 1.0 Hz. These findings demonstrate that during ECR, tangential acceleration along the interaural axis stimulates the utricular maculae, inducing horizontal eye movements in addition to those induced by the semicircular canal, thus resulting in an enhancement of VOR gain. Our results also suggest synergistic interactions of the otolith organs and semicircular canals. We conclude that ECR is a useful clinical test of the function of the otolith organs.

Animals↗
PubMedDate not supplied

Functional imaging of the human olfactory cortex by magnetic resonance imaging.

Our understanding of the neural mechanism of human olfaction is still equivocal. Several recent reports document that functional magnetic resonance imaging (MRI) has a potential to visualize dynamic brain function in humans without invasion. In the present study, we applied functional MRI with odor stimulation for the purpose of clarifying the localization of olfactory cortices in the human. We obtained a significant increase in cerebral blood flow in the piriform cortex, orbitofrontal cortex, and inferior medial frontal lobe, corresponding to olfactory cortices. These results suggest that, in the near future, precise diagnosis of the patients with olfactory disorders will be possible using functional MRI with odor stimulation.

Adult↗
PubMedDate not supplied

Recovery of the otolith-ocular reflex after unilateral deafferentation of the otolith organs in squirrel monkeys.

The enhancement of the vestibulo-ocular reflex (VOR) gain in the eccentric rotation is mediated by the otolith organs. Functional recovery of the otolith-ocular reflex after deafferentation of the otolith organs was examined in squirrel monkeys, using the enhancement of the eccentric VOR gain as an indicator of the reflex. After unilateral deafferentation of the otolith organs, the enhancement of the eccentric VOR gain decreased and then recovered completely within eight weeks. However, the eccentric VOR gain was not enhanced after contralateral side lesions. These findings demonstrate that functional recovery of the otolith-ocular reflex is achieved after unilateral deafferentation of the otolith organs, and that afferents from the remaining otolith organs are necessary for the functional compensation.

Animals↗
PubMedDate not supplied

Reorientation of poststimulus nystagmus in tilted humans.

Recent studies indicate that the direction of postrotatory nystagmus and optokinetic afternystagmus reorients toward earth-horizontal in tilted subjects. To further examine this phenomenon in humans, we studied 8 adults (4M, 4F) with no history of neurologic or otologic disease. Vestibular stimulation consisted of yaw off-vertical axis rotation (OVAR) trapezoids with eyes open in the dark at 60 degrees/s constant velocity with a tilt angle of 30 degrees and a deceleration at 100 degrees/s2 to a stop in either the right-ear-down or the left-ear-down position. The optokinetic stimulus consisted of 5 degrees wide black and white stripes projected against a cylindrical visual surround 1 m in diameter rotated at a constant velocity of 30 degrees/s. The projector, visual surround, and subject were all tilted by 30 degrees; subjects were placed either in the right-ear-down or left-ear-down position. Eye position was measured using the magnetic scleral search coil technique. Each trial was scrutinized for the presence of reorientation of nystagmus in the subject's roll plane by looking for vertical nystagmus in the appropriate direction. Results indicated that reorientation of postrotatory nystagmus following OVAR was variable but often present. Reorientation of optokinetic afternystagmus was neither as consistent nor as robust as that seen following OVAR. These findings confirm that humans exhibit a predilection for eye rotations in the earth-horizontal plane.(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗
PubMedDate not supplied

Influence of otolith organs, semicircular canals, and neck afferents on post-rotatory nystagmus.

The duration of post-rotatory nystagmus is known to be shortened by head tilt, a phenomenon that has been attributed to rapid discharge of the velocity storage mechanism. The relative importance of the various sensory signals associated with post-rotatory head tilt is unknown. Using both earth-vertical axis and off-vertical axis rotation, we investigated this issue in humans by combining sudden termination of constant velocity rotation with several post-rotatory maneuvers that stimulated combinations of otolith organ, somatosensory, and vertical semicircular canal afferents. Results indicated that horizontal post-rotatory nystagmus was shortened by maneuvers that move the head from upright to off-vertical and by cessation of dynamic otolith stimuli. Somatosensory, neck afferent, and transient vestibular stimulation had no consistent effect. We conclude that tilt suppression of postrotatory nystagmus and the short time constant following off-vertical axis rotation is primarily a function of otolith influence on the velocity storage system.

Adult↗
PubMedDate not supplied

Effects of caloric vestibular stimulation on parietal and temporal blood flow in human brain: a consecutive technetium-99m-HMPAO spect study.

The effects of caloric vestibular stimulation on regional cerebral blood flow (rCBF) of the parietal and temporal cortex were examined in 10 healthy volunteers. The consecutive 99mTe-hexamethyl-propyleneamine oxime (99mTc-HMPAO) single-photon emission computed tomography (SPECT) method with region of interest analysis was used. Changes in rCBF induced by caloric stimulation with cold air (25 degrees C) were evaluated in comparison with those induced by control stimulation with air at body temperature (37 degrees C). Caloric stimulation with cold air induced vertigo in 4 subjects, dizziness in 2, and no sensation of self-motion in the remaining 4 subjects, whereas, control stimulation did not induce the sensation of self-motion in any subject. Although both parietal and temporal rCBF were slightly decreased during caloric stimulation, a correlation could be established between the magnitude of left-right differences in change of parietal rCBF and the degree of self-motion perception induced by cold-air caloric stimulation, as compared to control stimulation. Left-right differences in change of parietal rCBF in subjects with vertigo during caloric stimulation were significantly higher than those in subjects without any sensation of self-motion. In contrast, there was no correlation between the magnitude of left-right difference in change of parietal rCBF and maximum slow phase eye velocity induced by caloric stimulation. These findings suggest that the parietal lobe is involved in the perception of vertigo due to vestibular stimulation, but not in the vestibulo-ocular reflex.

Adult↗