Eiju Watanabe

Three-dimensional digitizer (neuronavigator): New equipment for computed tomography-guided stereotaxic surgery

A new device was invented as an adjunct for computed tomography (CT)-guided stereotaxic or open neurosurgery. It is composed of a multijoint three-dimensional digitizer (sensor arm) and a microcomputer, which indicates the place of the sensor arm tip on preoperative CT images. Computed tomography scan is performed preoperatively with three markers placed on the nasion and ears. At surgery, after fixing the patients head and the sensor arm, sampling of the standard points was done to translate the position of the tip of the sensor arm onto the CT images displayed on a computer screen. In this way positional data from conventional preoperative CT scan can be directly transferred into the surgical field. This system has the unique feature of introducing CT-guided stereotaxis into conventional open neurosurgery.

Neuronal events correlated with long-term adaptation of the horizontal vestibulo-ocular reflex in the primate flocculus

The activity of flocculus Purkinje cells was examined in Japanese monkeys during sustained vestibular-visual stimulation which caused adaptation of the horizontal vestibulo-ocular reflex (H-VOR). In the floccular area related to the H-VOR by microstimulation. Purkinje cells consistently changed their simple spike responsiveness to head rotation in parallel with the adaptive H-VOR gain change. Similar changes occurred even after the H-VOR had been extinguished by lesioning of the vestibular nuclei. The complex spike discharge, on the other hand, modulated during vestibular-visual stimulation with a reciprocal pattern to the adaptive changes in the simple spike discharge. These results support the hypothesis that the flocculus adaptively modifies the H-VOR through their simple spike activity under the influence of visual climbing fiber signals.

Demonstration of zonal projections from the cerebellar flocculus to vestibular nuclei in monkeys (Macaca fuscata)

Purkinje cells in the flocculus of macaque monkeys were labeled by retrograde axonal transport of horseradish peroxidase from the vestibular nuclei. These neurons are organized in three adjacent, narrow bands which span all folia of the ipsilateral flocculus. The central band, 500-750 micrometer wide, projects to the medial vestibular nucleus, while the two adjacent bands, each 300-500 micrometer wide, innervate the superior vestibular nucleus. These three bands cover about one-half of the total area of the Purkinje cell layer of flocculus. Thus, the pattern of zonal projections in monkeys is the same as reported in rabbits and cats.

Role of the primate flocculus in adaptation of the vestibulo-ocular reflex

Neuronal events associated with adaptation of the horizontal vestibulo-ocular reflex (HVOR) induced by sustained vestibular-visual mismatching were investigated in the primate flocculus. The floccular area related to the HVOR (H-zone) was identified by electrical micro-stimulation which induced ipsilaterally directed horizontal eye movement. It was thus found that Purkinje cells in the H-zone consistently changed their simple spike responses to head rotation in parallel with the adaptive HVOR gain change. This was demonstrated by observing the change of simple spike firing of Purkinje cells during adaptation of HVOR either in a population study or an individual study. Since similar changes occurred even after bilateral lesioning of vestibular nuclei had extinguished the HVOR, these changes appear to represent vestibular, but not eye velocity, mossy fiber responsiveness. The complex spike discharge, on the other hand, modulated during vestibular-visual stimulation with a reciprocal pattern to the adaptive changes in the simple spike discharge. These results are consistent with the hypothesis that the flocculus Purkinje cells adaptively control the HVOR through their simple spike activity under influences of retinal error signals conveyed by visual climbing fiber pathways.

Functional representation of eye movements in the flocculus of monkeys (Macaca fuscata)

The flocculus of the monkey was mapped with microstimulation methods in chronic preparations. Three types of low threshold, disconjugate eye movements were elicited: (1) a lateral deviation of the ipsilateral eye, (2) a downward deviation of the ipsilateral eye and (3) counterclockwise rotation of the ipsilateral eye. Horizontal eye movements were obtained from folia 2, 3, 4 and 6-10 of the flocculus, and the region eliciting horizontal eye movements was traced in the sagittal plane over a distance of 4 mm in one animal. However, sites flanking these horizontal movement sites produced either vertical movements, rotatory movements or failed to produce a movement of either eye. These findings suggest a zonal organization of flocculus functions in monkeys that is consistent with the differential projections of flocculo-vestibular connections revealed by retrograde tracing studies [2].

Evidence of a collateralized climbing fiber projection from the inferior olive to the flocculus and vestibular nuclei in rabbits

In albino rabbits, horseradish peroxidase injections confined to vestibular nuclei retrogradely labeled neurons in the dorsal cap of the contralateral inferior olive. Mapping with stimulating electrodes revealed that stimulation of the lateral aspect of the medial vestibular nucleus and the medial aspect of the inferior vestibular nucleus evoked field potentials representing antidromic activation of contralateral dorsal cap neurons. These responses interfered with the antidromic response evoked from the contralateral flocculus and orthodromic responses evoked from the contralateral retina, suggesting that dorsal cap neurons which both receive retinal input and project to the flocculus send collaterals to vestibular nuclei.

Loss of vision-guided adaptation of the vestibulo-ocular reflex after depletion of brain serotonin in the rabbit.

Brain serotonin in pigmented rabbits was depleted by intraventricular injection of 5,7-dihydroxytryptamine (5,7-DHT). Before depletion, an adaptive increase in the gain of the horizontal vestibulo-ocular reflex (HVOR) could be induced regularly by continuously rotating the animals in combination with optokinetic stimulus. After the depletion, such an increase in HVOR gain did not occur, even though dynamic characteristics of the HVOR and of the optokinetic eye movement were not altered. 5,7-DHT treatment also reduced brain norepinephrine, but depletion of norepinephrine to a similar extent by intraventricular injection of 6-hydroxydopamine in other rabbits did not affect the HVOR adaptation. These results suggest that brain serotonin plays an important role in maintaining adaptive modifiability of the HVOR.

How Does Mannitol Reduce Edema Water in Focal Cerebral Ischemia

The development of massive brain edema following cerebral ischemia is sometimes a matter of great concern. The use of hyperosmolar agents like mannitol or glycerol is still the first and most effective treatment, but long term systemic use is not always possible, because of side effects such as systemic dehydration or disturbance of electrolyte balance. Although the fact that mannitol reduces the intracranial pressure in such a situation is well known (4), it is not yet fully understood whether mannitol actually reduces edema water, or if so, from which compartment of the brain (2). In the present study, we have developed a new technique which allows enough of the agents perfused to reach a high concentration throughout the ischemic tissue, and investigated the action of mannitol to shed further light on these questions.