Chiharu Sekiguchi

Inhibition of Bone Resorption by Pamidronate Cannot Restore Normal Gain in Cortical Bone Mass and Strength in Tail‐Suspended Rapidly Growing Rats

To clarify how the changes in bone formation and resorption affect bone volume and strength after mechanical unloading, the effect of inhibition of bone resorption by a potent bisphosphonate, pamidronate, on bone mineral density (BMD), histology, and strength of hind limb bones was examined using tail‐suspended growing rats. Tail suspension for 14 days reduced the gain in the BMD of the femur at both the metaphysis rich in trabecular bone and the diaphysis rich in cortical bone. Treatment with pamidronate increased the total BMD as well as that of the metaphysis of the femur but had almost no effect on the BMD of the diaphysis in both control and tail‐suspended rats. Histological examinations revealed that 14‐day tail suspension caused a loss of secondary cancellous bone with a reduction in the trabecular number and thickness in comparison with control rats. In the femoral diaphysis, the diameter and cortical bone thickness increased to a lesser degree in tail‐suspended rats when compared with rats without tail suspension, and a marked reduction in bone formation and the layers of alkaline phosphatase–positive cells was observed at the periosteal side. Pamidronate treatment increased secondary cancellous bone but could not restore normal growth‐induced periosteal bone apposition and bone strength. Because the material strength of the femoral diaphysis at the tissue level was not affected by pamidronate treatment, the inability of pamidronate to prevent the reduction in physical strength of the femoral diaphysis does not appear to be due to a change in the quality of newly formed bone. These results demonstrate that tail suspension reduces the growth‐induced periosteal modelling drift and that the antiresorptive agent pamidronate is unable to restore normal periosteal bone apposition.

Effects of 14 days of spaceflight and nine days of recovery on cell body size and succinate dehydrogenase activity of rat dorsal root ganglion neurons

The cross-sectional areas and succinate dehydrogenase activities of L5 dorsal root ganglion neurons in rats were determined after 14 days of spaceflight and after nine days of recovery. The mean and distribution of the cross-sectional areas were similar to age-matched, ground-based controls for both the spaceflight and for the spaceflight plus recovery groups. The mean succinate dehydrogenase activity was significantly lower in spaceflight compared to aged-matched control rats, whereas the mean succinate dehydrogenase activity was similar in age-matched control and spaceflight plus recovery rats. The mean succinate dehydrogenase activity of neurons with cross-sectional areas between 1000 and 2000 microns2 was lower (between 7 and 10%) in both the spaceflight and the spaceflight plus recovery groups compared to the appropriate control groups. The reduction in the oxidative capacity of a subpopulation of sensory neurons having relatively large cross-sectional areas immediately following spaceflight and the sustained depression for nine days after returning to 1 g suggest that the 0 g environment induced significant alterations in proprioceptive function.

Factor structure of psychobiological seven-factor model of personality: a model-revision

Abstract The purpose of this study was to examine the factor structure in the Temperament and Character Inventory [TCI; Cloninger, C. R., Svrakic, D. M., & Przybeck, T. R. (1993). A psychobiological model of temperament and character. Archives of General Psychiatry, 50, 975–990.] and to determine appropriate subscales and items to assess the psychobiological seven-factor model with a nonclinical Japanese sample by the use of the TCI short version. Among 383 ex-members of the Japanese Antarctic Research Expedition, confirmatory factor analysis of the TCI showed that temperament consisted of four factors and character of three, as the original model suggested. Harm Avoidance, Reward Dependence, Self Transcendence and Cooperativeness may be interpreted as a constellation of interrelated but possibly discrete dimensions. Most of the items were loaded into each corresponding subscale, although a few of the items were not confirmed as appropriate. Implications and the future direction of personality research are discussed.

Influence of Spaceflight on Succinate Dehydrogenase Activity and Soma Size of Rat Ventral Horn Neurons

Succinate dehydrogenase (SDH) activities and soma cross-sectional areas (CSA) of neurons in the dorsolateral region of the ventral horn at the L5 segmental level of the spinal cord in the rat were determined after 14 days of spaceflight and after 9 days of recovery on earth. The results were compared to those in age-matched ground-based control rats. Spinal cords were quick-frozen, and the SDH activity and CSA of a sample of neurons with a visible nucleus were determined using a digitizer and a computer-assisted image analysis system. An inverse relationship between CSA and SDH activity of neurons was observed in all groups of rats. No change in mean CSA or mean SDH activity or in the size distribution of neurons was observed following spaceflight or recovery. However, there was a selective decrease in the SDH activity of neurons with soma CSA between 500 and 800 microns2 in the flight rats, and this effect persisted for at least 9 days following return to 1 g. It remains to be determined whether the selected population of motoneurons or the specific motor pools affected by spaceflight may be restricted to specific muscles.

Comparison of the response of motoneurons innervating perineal and hind limb muscles to spaceflight and recovery.

The succinate dehydrogenase (SDH) activities and cell body sizes of motoneurons in the dorsomedial (DM) region of the ventral horn at the lower portion of the L5 and the L6 segmental levels of the rat spinal cord were determined following 14 days of spaceflight and after 9 days of recovery on Earth and compared with those in the retrodorsolateral (RDL) region of the ventral horn at the same segmental levels. No changes in the mean SDH activity of motoneurons in the DM region were observed following spaceflight or after recovery. However, a decrease in the mean SDH activity of motoneurons with cell body sizes between 500 and 900 μm2 in the RDL region was observed following spaceflight and after recovery. These data indicate that moderate‐sized motoneurons in the RDL region, which are most likely associated with the hind limb musculature, were responsive to the microgravity environment. In contrast, the motoneurons in the DM region associated with the perineal muscles (associated with predominantly fast, low‐oxidative muscles which are recruited for relatively brief periods at high activation levels and have no load‐bearing function at 1G) were not affected by microgravity.

Effects of 10 Min Tilt and Visual Directional Information on Ocular Counterrolling

The effects of 10 min of static tilt on ocular counterrolling (OCR) were investigated. Seven healthy volunteers were tilted 45 degrees around the naso-occipital axis, fixed at that position for 10 min, and the pre- and post-tilt OCRs were recorded. OCR was video-recorded using an infrared CCD camera and subjected to computer image analysis. The subjects were directed to fixate on an imagined target in the dark (experiment 1), or viewed an earth vertical, striped pattern placed in front of his/her eyes to enhance the recognition of extent of body tilt (experiment 2). In experiment 1, the average OCRs recorded before and after 10 min of tilt showed no significant changes. However, in experiment 2, OCR decreased significantly after 10 min of tilt. These results suggest that visual perception of spatial verticality can produce time-dependent adaptation of OCR.

Effect of transdermally administered scopolamine on the vestibular system in humans

In order to elucidate the effect of scopolamine on the vestibular system in humans, various experimentally-induced forms of nystagmus, i.e. caloric nystagmus, rotational nystagmus, optokinetic nystagmus, visual-vestibular interaction and optokinetic after nystagmus, were evaluated before and after the administration of two pieces of Scopoderm-TTS or placebo patches retro-auricularly. Scopolamine reduced the responses of both the caloric and optokinetic after nystagmus compared with the placebo. The possible action site of this drug is discussed.

Effect of head up tilt on cerebral circulation.

This study was performed to study the effect of the head up tilt (HUT) on cerebral circulation across the time course (60 degrees HUT for 15 minutes) and across the different angles of HUT (15, 30, 45, 60 degrees HUT for 15 minutes). Cerebral circulation was continuously monitored during 15 minutes of HUT by the carotid Doppler flow meter, the transcranial Doppler flow meter, and the near infra-red spectrophotometer. The results show that the cerebral blood flow decreased during HUT and that the cerebral blood volume decreased initially and then gradually increased. And the magnitude of the effect may have the relationship with the angles of the HUT.

Eye Movement Elicited by Linear Acceleration

So far, stimuli to investigate eye movement elicited by the otolith organ have been mainly given by parallel swing, counter rolling, up and down motion or eccentric rotation. In this paper we report eye movement of normal subjects stimulated by sinusoidal lateral linear acceleration on a sled chair. This work is a part of the space medicine research program in Japan.