Neuronal intranuclear hyaline inclusion disease with rapidly progressive neurological symptoms

This report describes a male patient who presented with symptoms suggestive of spinocerebellar degeneration and who died of respiratory failure at the age of 7 years but was diagnosed, at autopsy, as having neuronal intranuclear hyaline inclusion disease. Neuronal intranuclear hyaline inclusion disease is a progressive and degenerative disease; diagnosis is possible only by neuropathological analysis. This is a rare disorder; few cases with early childhood onset and rapidly progressive neurologic symptoms have been documented. According to previous reports, most neurons in the central nervous system exhibited intranuclear eosinophilic inclusion bodies; neuronal depletion appeared to be restricted to the cerebellar cortex and the medullary inferior olivary nuclei, consistent with the fact that clinical deficit appears to correspond to the site of neuronal depletion and not to where eosinophilic bodies are detected. Immunohistochemical analysis revealed that these inclusions were positive for ubiquitin. The case presented herein clearly indicates that neuronal intranuclear hyaline inclusion disease should be considered as a differential diagnosis of cases involving spinocerebellar degeneration with childhood onset.

Immunohistopathological study of the oral lichenoid lesions of chronic GVHD

BACKGROUND

Chronic graft-vs.-host disease (cGVHD) is a common and serious complication after bone marrow transplantation (BMT). However, the detailed process of oral lichenoid lesions of cGVHD is still unknown. Therefore, we investigated the immunohistopathological features of cGVHD compared with oral lichen planus (OLP) and healthy controls.

METHODS

Nineteen allogenic BMT recipients with a histopathological diagnosis of cGVHD were investigated. We investigated the immunohistopathological features of cGVHD compared with OLP and healthy controls.

RESULTS

Immunohistopathological features showed that the infiltrations of CD4-positive T cells of cGVHD and OLP were significantly larger than those of the normal oral mucosa (P < 0.005). A larger number of CD8-positive T cells was infiltrated in cGVHD and OLP compared with the normal oral mucosa (P < 0.001). The difference in the number of CD4- and CD8-positive T cells between cGVHD and OLP was not significant. The infiltrations of Langerhans cells (CD1a) in cGVHD and OLP were significantly larger than those in the normal oral mucosa (P < 0.005). The difference in the number of Langerhans cells between cGVHD and OLP was not significant. CD68-positive macrophages were more frequently seen in cGVHD and OLP than in the normal oral mucosa (P < 0.0001). The difference in the number of CD68-positive macrophages between cGVHD and OLP was not significant.

CONCLUSIONS

It is suggested that Langerhans cells and CD8-positive T cell may play a major role in the pathogenesis of the oral lichenoid lesions of cGVHD, and the immune response was inducted in OLP as well as the oral lichenoid lesion of cGVHD in this study.

Autonomic Neural Functions in Space

Autonomic neural functions are important to regulate vital functions in the living body. There are different methods to evaluate indirectly and directly autonomic, sympathetic and parasympathetic, neural functions of human body. Among various methods, microneurography is a technique to evaluate directly sympathetic neural functions in humans. Using this technique sympathetic neural traffic leading to skeletal muscles (muscle sympathetic nerve activity; MSNA) can be recorded from human peripheral nerves in situ. MSNA plays essentially important roles to maintain blood pressure homeostasis against gravity. Orthostatic intolerance is an important problem as an autonomic dysfunction encountered after exposure of human beings to microgravity. There exist at least two different types of sympathetic neural responses, low and high responders to orthostatic stress in orthostatic hypotension seen in neurological disorders. To answer the question if post-spaceflight orthostatic intolerance is induced by low or high MSNA responses to orthostatic stress, MSNA was microneurographically recorded for the first time before, during and after spaceflight in 1998 under Neurolab international research project. The same activity has been recorded during and/or after ground-based short- and long-term simulations of microgravity. MSNA was rather enhanced on the 12(th) and 13(th) day of spaceflight and just after landing day. Postflight MSNA response to head-up tilt was well preserved in astronauts who were orthostatically well tolerant. MSNA was suppressed during short-term simulation of microgravity less than 2 hours but was enhanced after long-term simulation of microgravity more than 3 days. Orthostatic intolerance after exposure to long-term simulation of microgravity was associated with reduced MSNA response to orthostatic stress with impaired baroreflex functions. These findings obtained from MSNA recordings in subjects exposed to space as well as short- and long-term simulations of microgravity indicate that sympathetic neural control is lowered when exposed to short-term microgravity but becomes enhanced after exposure to long-term microgravity. A lack of enhanced sympathetic neural response to orthostatic stress may induce orthostatic intolerance. Based on these findings effective countermeasures should be developed to prevent autonomic dysfunctions induced by exposure to microgravity. These include development of prescription and devices of physical exercise, electrical and magnetic nerve stimulations, body vibration, elastic bandage and stocking, lower body negative pressure, artificial gravity, medical drugs, and combinations of them. These countermeasures will be beneficial to prevent autonomic dysfunctions related to gravitational stress such encountered in bedridden subjects as orthostatic hypotension, atrophy of antigravity muscles and so on. This is particularly important in the present aged-society with many bedridden elderly people. The knowledge accumulated from studies on autonomic neural functions in space should be very useful to establish effective countermeasures and preventive methods for gravity-dependent autonomic dysfunctions.

Self-assembly of concentric quantum double rings

We demonstrate the self-assembled formation of concentric quantum double rings with high uniformity and excellent rotational symmetry using the droplet epitaxy technique. Varying the growth process conditions can control each ring's size. Photoluminescence spectra emitted from an individual quantum ring complex show peculiar quantized levels that are specified by the carriers' orbital trajectories.

Microneurographically Recorded Ia Discharge from the Tibial Nerve Mainly Transmits the Angular Velocity of the Ankle Joint in Humans

Investigations of the Ia afferent discharge in clarifying problems in disused and malused skeletal muscles have been carried out mainly in muscles of the upper extremities. However, such problems actually occur more frequently in the antigravity muscles of the lower extremities, such as the triceps surae muscle. An analysis of microneurographically recorded Ia discharges from the tibial nerve innervating the triceps surae muscle during dynamic movement of the ankle joint indicated that they mainly transmitted information on the angular velocity of the joint. However, the information on the position sense of the joint was not as well transmitted through Ia discharges. There was no correlation between the joint angle and the static response. However, the dynamic response of a Ia afferent was well correlated to the angular velocity. It is concluded that the human proprioception of the triceps surae muscle was not dependent on the position of the ankle joint, but largely on its movement by the stretching of the muscle.

Changes in spontaneous baroreflex sensitivity during sleep in humans

To evaluate changes in the spontaneous baroreflex sensitivity for heart rate and for muscle sympathetic nerve activity (MSNA) during sleep, we simultaneously recorded MSNA from the tibial nerve and monitored ECG, EEG, EOG, EMG and blood pressure during the resting awake stage and sleep. Blood pressure, ECG and MSNA waves were changed to equidistant time series data of each second by cubic spline interpolation. Cross correlations between the MSNA and diastolic blood pressure and between the instantaneous heart rate and systolic blood pressure were analyzed. Spontaneous baroreflex sensitivities for MSNA and for heart rate were assessed from the slope of the regression lines for each. During sleep, the spontaneous baroreflex sensitivity for MSNA gradually decreased as the non-REM sleep stages advanced. Spontaneous baroreflex sensitivity for heart rate did not show any apparent changes. These results suggest that baroreflex modulations for heart rate and for MSNA differ during sleep.

Short term fluctuations in muscle sympathetic nerve activity in man

In order to characterize the variability of muscle sympathetic nerve activity (MSNA), resting MSNA was recorded for over 30 min in 4 healthy young subjects in the supine position in a thermoneutral environment. Spectral analysis was applied to the integrated traces of MSNA and to the heart rate using maximum entropy method. Both MSNA and the heart rate spectra exhibited periodic peaks, which were superimposed on the general 1/f-like structure, at around 0.02 Hz, 0.1 Hz, 0.25 Hz and 1.0 Hz. However, the periodic peak at 0.1 Hz in the MSNA spectra was more prominent than in the heart rate spectra at the same frequency. These findings suggest that MSNA variability may have a closer causal relationship with Mayer's rhythm than with heart rate fluctuations.

Effects of aging on the arterial baroreflex control of muscle sympathetic nerve activity in healthy subjects

To determine how arterial baroreflex gains for sympathetic nerve activity are affected by aging, muscle sympathetic nerve activity (MSNA) from the tibial nerve was monitored by microneurography, and heart rate and blood pressure were recorded for the pressor or depressor responses to intravenous injections of phenylephrine or nitroglycerin in 22 healthy humans, aged 16 to 57 years old. Although the arterial baroreflex gain for the heart rate showed attenuation by aging, the gain for MSNA was not affected by aging. These data suggest a preservation of the arterial baroreflex control of sympathetic nerve activity despite attenuation of the arterial baroreflex control of the heart rate with aging in humans.

Human cardiovascular responses to a 60-min bath at 40 degrees C

This study was designed to determine human cardiovascular responses to a 60-min bath at 40 degrees C compared with a thermoneutral bath at 34.5 degrees C. We measured mean blood pressure (MBP), heart rate (HR), skin blood flow (SBF) and core temperature in 8 healthy young males bathing at two different temperatures, 34.5 degrees C and 40 degrees C. During the thermoneutral bath (34.5 degrees C), heart rate tended to decrease, but all other variables showed no significant change. Ten min after entering the 40 degrees C bath, MBP decreased while HR and SBF increased. At the same time core temperature increased. We conclude that bathing at 40 degrees C may induce remarkable changes in the cardiovascular system by increasing core temperature when immersion in a hot bath for more than 10 min.

Sympathetic nerve activity in hypotension and orthostatic intolerance

AIM

The present paper reviews how changes in sympathetic nerve activity are related to hypotensive episodes and orthostatic intolerance in humans.

RESULTS

It has been well documented that sympathetic neural traffic to skeletal muscles (muscle sympathetic nerve activity; MSNA) plays an essential role in maintaining blood pressure homeostasis mainly through baroreflex. The MSNA responded to gravitational loading from the head to the leg (+Gz) during passive head-up tilt (HUT). Patients who suffered from orthostatic hypotension with or without syncope were classified into at least two groups; low and high responders of MSNA to orthostatic loading. The typical examples belonging to the former group were patients of multiple system atrophy who had very low basal sympathetic outflow to muscle which responded extremely poorly to HUT. Patients of multiple system atrophy presented also postprandial hypotension in which muscle sympathetic response to oral glucose administration was absent. The latter group was represented by subjects who manifested vasovagal syncope with normal or even higher muscle sympathetic response to HUT, which was suddenly withdrawn concomitantly with bradycardia and hypotension. Similar withdrawal of sympathetic nerve traffic to muscle was encountered in a rare case of idiopathic non-orthostatic episodic hypotension which accompanied bradycardia. The MSNA was suppressed by short-term exposure to microgravity but was enhanced after long-term exposure to microgravity. Orthostatic intolerance after long-term exposure to microgravity was related to progressive reduction of muscle sympathetic response to orthostatic loading with impaired arterial baroreflex.

CONCLUSION

It is concluded that hypotensive episodes are closely related to poor or lack of muscle sympathetic outflow, but may depend on various neural mechanisms to induce it.

Role of the sympathetic nervous system in the generation of one-minute wave in body fluid volume during upright standing

In clarifying the role of sympathetic nerve outflow to the muscles in the genesis of one-minute waves in body fluid volume, power spectral analysis of muscle sympathetic nerve activity (MSNA) was performed. MSNA was recorded by microneurography in an upright standing position simultaneously with the measurements of body circumference, venous pressure at the dorsum pedis veins, intrathoracic fluid volume, soleus EMG, and calf fluid volume. Subjects were seven healthy male volunteers aged 18 to 32 years. Spectral analysis revealed the one-minute oscillation in MSNA as well as in other variables. Cross spectral analysis between the soleus EMG and each variable revealed a phase order of the one-minute oscillations. It was as follows: 1) an increase in calf fluid volume; 2) a decrease in intrathoracic fluid volume; 3) an increase in venous pressure at the dorsum pedis veins; 4) an increase in the soleus EMG activation; 5) an activation of MSNA; 6) a decrease in calf fluid volume; and 7) an increase in intrathoracic fluid volume. It is concluded that sympathetic nerve activity as well as cardiovascular variables have a cyclic rhythm with a duration of one minute to maintain hemodynamic homeostasis in humans in an upright standing position.

[Effects of gravitational unloading on blood supply of working muscles]

Exposure to the conditions of simulated gravitational unloading (head down tilting, dry immersion) produces a material effect on blood supply of working muscles in humans that may depend on type of work (local or global) and posture (vertical or horizontal). Peak blood flow in the calf after exposure to HDT and dry immersion reduces by 7 to 20% and the post-contraction hyperemia (PCH) following a standard work of the calf extensors noticeably increases. In contrast to PCH, blood flow during natural locomotion diminishes as a result of simulated gravitational unloading. Standard bicycling by sitting and supine human subjects moderates and exaggerates the post-work hyperemia, respectively. Consideration is given to possible causes of these effects.

A comparative cytogenetic study of chromosome homology between chicken and Japanese quail

In order to construct a chicken (Gallus gallus) cytogenetic map, we isolated 134 genomic DNA clones as new cytogenetic markers from a chicken cosmid DNA library, and mapped these clones to chicken chromosomes by fluorescence in situ hybridization. Forty-five and 89 out of 134 clones were localized to macrochromosomes and microchromosomes, respectively. The 45 clones, which localized to chicken macrochromosomes (Chromosomes 1-8 and the Z chromosome) were used for comparative mapping of Japanese quail (Coturnix japonica). The chromosome locations of the DNA clones and their gene orders in Japanese quail were quite similar to those of chicken, while Japanese quail differed from chicken in chromosomes 1, 2, 4 and 8. We specified the breakpoints of pericentric inversions in chromosomes 1 and 2 by adding mapping data of 13 functional genes using chicken cDNA clones. The presence of a pericentric inversion was also confirmed in chromosome 8. We speculate that more than two rearrangements are contained in the centromeric region of chromosome 4. All 30 clones that mapped to chicken microchromosomes also localized to Japanese quail microchromosomes, suggesting that chromosome homology is highly conserved between chicken and Japanese quail and that few chromosome rearrangements occurred in the evolution of the two species.

Long-term response to zonisamide in patients with West syndrome

The long-term effectiveness of zonisamide (ZNS) was evaluated in 11 patients with West syndrome (7 symptomatic) who had cessation of spasms with ZNS monotherapy. During the follow-up period (24 to 79 months, mean = 53 months), this response was maintained in 7 patients (3 symptomatic, relapse rate = 36%), including 2 children in whom ZNS was successfully discontinued. No serious adverse reactions were noted. ZNS may be both effective and well tolerated for the treatment of West syndrome.

Enhanced Hoffman-reflex in human soleus muscle during exposure to microgravity environment

Responses of Hoffman-reflex in the soleus muscle to changes of gravity levels created by parabolic flight of a jet airplane were investigated in four healthy male subjects. The subjects maintained a sitting position with seat belts fastened, keeping the anterior ankle and posterior knee angles at approximately 135 degrees. The gravity levels were altered from 1- to 2-G, and then microgravity was created for approximately 20 s. The levels were recovered from 1.5- to 1-G during the descending phase. The time interval between the stimulation and either M- or H-wave was not influenced by the changes in gravity levels. The amplitude of the M-wave during hyper- and microgravity was identical to that obtained at 1-G. However, the H-wave amplitude was increased when the subjects were exposed to microgravity (approximately four times vs. 1-G level). The H/M ratio was also elevated during microgravity. Further, such a phenomenon was maintained throughout the 20 s of microgravity exposure. Hypergravity at 1.5- or 2-G had no effect on the H-wave amplitude. It is suggested that an acute exposure to microgravity increases the excitability of the soleus motor pool and the increased excitability is restored immediately when the gravity level is elevated.

Influence of vestibulo-sympathetic reflex on muscle sympathetic outflow during head-down tilt

To clarify the response of muscle sympathetic nerve activity (MSNA) to static stimulation of otolith organs in a craniocaudal direction (+Gz) in humans, we examined the effect of otolith stimulation on MSNA without changing the effect of cardiopulmonary baroreceptors using a 6-8.5 degrees head-down tilt (HDT) and lower body negative pressure (LBNP) device. Before the study, we established that 6-8.5 degrees HDT with 10 mmHg LBNP caused a fluid shift to the degree that the thoracic impedance was the same as the supine position without LBNP. Subjects were young male volunteers aged 22.1 +/- 3.8 years who gave informed consent. MSNA was recorded from the tibial nerve by microneurography simultaneously with heart rate (ECG), thoracic fluid volume (impedance method), and blood pressure (tonometric method). During 6-8.5 degrees HDT with 10 mmHg LBNP, MSNA was suppressed slightly without significantly changing heart rate, thoracic impedance, or mean arterial blood pressure. The results suggest that the sympathosuppression was related not to the result of cardiopulmonary [correction of cardioplumonary] loading but to the -Gz change (caudocranial direction [correction of dirction]) of 0.1 G. It is estimated that the vestibulo-sympathetic reflex may suppress sympathetic outflow to muscles in humans.

Tissue-specific expression of an anti-proliferative hybrid transgene from the human smooth muscle alpha-actin promoter suppresses smooth muscle cell proliferation and neointima formation

The retinoblastoma protein (Rb), a key regulator of cell cycle progression, can bind the transcription factor E2F converting it from a positive transcriptional factor capable of driving cells into S phase into a negative complex which arrests cells in G1. We have created a potent transcriptional repressor of E2F-dependent transcription by fusing the C-terminal fragment of Rb (p56) to the DNA and DP1-binding domains of E2F. Because the expression of E2F/56 fusion protein from a constitutive promoter was incompatible with virus growth, adenovirus constructs were prepared where transgenes were expressed from a fragment of the smooth muscle alpha-actin (SMA) promoter. Immunoblot and beta-galactosidase staining demonstrated smooth muscle-specific expression of this transcriptional element in vitro. The SMA-p56 and SMA-E2F/p56 adenoviral constructs also induced G0/G1 cell cycle arrest specifically in smooth muscle cells. Following administration to rat tissues, the SMA-beta-galactosidase construct exhibited expression in balloon-injured carotid arteries, but not in liver, bladder or skeletal muscle. Local delivery of the SMA-E2F/p56 adenoviral construct to balloon-injured carotid arteries inhibited intimal hyperplasia. Our results demonstrate that local delivery of the SMA-E2F/p56 adenoviral construct can limit intimal hyperplasia in balloon-injured vessels, while avoiding toxicity that could occur from the dissemination and expression of the viral transgene.

Effect of simulated microgravity exposure on thermoregulatory control of sweating

The purpose of the present study was to investigate the alterations in thermoregulatory control following 14 days of head-down bed rest (HDBR). The threshold temperature for sweating onset and sweating sensitivity were determined from sweating rates on the chest and forearm, and tympanic temperature as an index of core temperature (Tc) in nine healthy males exposed to a 60-min heat stress with a water-perfused blanket before and after HDBR. The threshold temperature for sweating onset, that is, the Tc at which sweating began on the chest and forearm was 36.75 +/- 0.14 and 36.72 +/- 0.13 degrees C before HDBR, respectively. The value significantly increased to 37.05 +/- 0.09 (p<0.05) for the chest and 37.04 +/- 0.08 degrees C (p<0.05) for the forearm after HDBR. On the other hand, the sweating sensitivity which was indicated as a slope of the Tc-sweating rate relationship significantly decreased from 4.20 +/- 1.15 to 2.32 +/- 1.18 for the chest (p<0.05) and from 4.20 +/- 1.06 to 2.92 +/- 0.98 mg/min/cm2/degrees C for the forearm (p<0.05) after HDBR. These findings suggest that the heat-dissipatory function was attenuated after 14 days of HDBR.

Long-term administration of amlodipine prevents decompensation to diastolic heart failure in hypertensive rats

OBJECTIVES; We assessed the effects of long-term amlodipine administration in a diastolic heart failure (DHF) rat model with preserved systolic function as well as the relationship between changes in left ventricular (LV) myocardial stiffening and alterations in extracellular matrix.

BACKGROUND

Although the effect of long-term administration of amlodipine has been shown to be disappointing in patients with systolic failure, the effect is unknown in those with DHF.

METHODS

Dahl salt-sensitive rats fed a high-salt diet for seven weeks were divided into three groups: eight untreated rats (DHF group), eight rats given high-dose amlodipine (10 mg/kg/day; HDA group) and seven rats given low-dose amlodipine (1 mg/kg/day; LDA group).

RESULTS

High-dose administration of amlodipine decreased systolic blood pressure and controlled excessive hypertrophy, without a decrease in the collagen content, and prevented the elevation of LV end-diastolic pressure at 19 weeks. Low-dose administration of amlodipine with subdeppressive effects did not control either hypertrophy or fibrosis; however, it prevented myocardial stiffening and, hence, the elevation of LV end-diastolic pressure. The ratio of type I to type III collagen messenger ribonucleic acid levels was significantly lower in both the HDA and LDA groups than in the DHF group.

CONCLUSIONS

Long-term administration of amlodipine prevented the transition to DHF both at the depressor and subdepressor doses. Amlodipine did not decrease the collagen content, but attenuated myocardial stiffness, with inhibition of the phenotype shift from type III to type I collagen. Thus, amlodipine may exert beneficial effects through amelioration of collagen remodeling in the treatment of DHF.

Static handgrip exercise modifies arterial baroreflex control of vascular sympathetic outflow in humans

To examine effects of static exercise on the arterial baroreflex control of vascular sympathetic nerve activity, 22 healthy male volunteers performed 2 min of static handgrip exercise at 30% of maximal voluntary force, followed by postexercise circulatory arrest (PE-CA). Microneurographic recording of muscle sympathetic nerve activity (MSNA) was made with simultaneous recording of arterial pressure (Portapres). The relationship between MSNA and diastolic arterial pressure was calculated for each condition and was defined as the arterial baroreflex function. There was a close relationship between MSNA and diastolic arterial pressure in each subject at rest and during static exercise and PE-CA. The slope of the relationship significantly increased by >300% during static exercise (P < 0.001), and the x-axis intercept (diastolic arterial pressure level) increased by 13 mmHg during exercise (P < 0.001). These alterations in the baroreflex relationship were completely maintained during PE-CA. It is concluded that static handgrip exercise is associated with a resetting of the operating range and an increase in the reflex gain of the arterial barorelex control of MSNA.

Ventricular production of natriuretic peptides and ventricular structural remodeling in hypertensive heart failure

OBJECTIVES

Brain natriuretic peptide (BNP) is a strong predictor of left ventricular (LV) hypertrophy (LVH) and dysfunction. However, our recent studies suggested that LVH is not necessarily associated with enhanced production of BNP in hypertension. This study aimed to clarify the relation of the characteristics of hypertrophy with the degree of gene expression of BNP in the developmental process of hypertensive heart failure.

METHODS

Serial changes in LV geometry, histology and atrial natriuretic peptide (ANP) and BNP mRNA levels, were assessed in a hypertensive heart failure model using Dahl salt-sensitive rats (n = 24). We further studied effects of alpha1-receptor antagonist (doxazosin: 1 mg/kg per day, n = 5) and angiotensin II type 1 receptor (AT1R) antagonist (candesartan cilexetil: 1 mg/kg per day, n = 5).

RESULTS

The BNP mRNA level was not elevated at the compensatory hypertrophic stage when ANP mRNA level was elevated. BNP mRNA level was increased with further progression of hypertrophy and development of fibrosis. AT1R blockade prevented such fibrosis and further progression of hypertrophy with normalization of BNP mRNA levels. Compensatory hypertrophy was not suppressed; therefore, ANP mRNA level, although decreased, was still beyond the normal level. The alpha1-receptor blockade slightly attenuated LV hypertrophy with a slight decrease in ANP mRNA levels. LV fibrosis was not prevented, and the BNP mRNA level was not decreased.

CONCLUSIONS

BNP gene expression is not enhanced by initial compensatory hypertrophy, but is enhanced by LV fibrosis and late stage progression of hypertrophy dependent on AT1R-mediated signaling pathway.

Muscle sympathetic nerve activity in blood pressure control against gravitational stress

Muscle sympathetic nerve activity (MSNA) can be directly recorded from human peripheral nerves in situ using microneurography. MSNA plays an essential role to control systemic blood pressure against gravitational stress. MSNA was enhanced by changing posture against terrestrial gravity from lying to sitting, and from sitting to standing. This activity was enhanced by head-up tilt depending on the gravitational input from the head to the leg (+Gz) in the human body. Orthostatic hypotension occurred when MSNA response to gravitational stress was impaired both in high and low responders of this sympathetic outflow. Syncope was preceded and/or associated by a withdrawal of MSNA. MSNA was suppressed by short-term exposure to microgravity but was enhanced after long-term exposure to microgravity. Orthostatic intolerance after exposure to prolonged microgravity was associated with a reduction of increased MSNA response to gravitational stress. Aging influenced gravity-related responses of MSNA.

Effects of lower body positive pressure on muscle sympathetic nerve activity response to head-up tilt

The present study was performed to test the hypothesis that application of lower body positive pressure (LBPP) during orthostasis would reduce the baroreflex-mediated enhancement in sympathetic activity in humans. Eight healthy young men were exposed to a 70 degrees head-up tilt (HUT) on application of 30 mmHg LBPP. Muscle sympathetic nerve activity (MSNA) was microneurographically recorded from the tibial nerve, along with hemodynamic variables. We found that in the supine position with LBPP, MSNA remained unchanged (13.4 +/- 3.3 vs. 11.8 +/- 2.3 bursts/min, without vs. with LBPP; P > 0.05), mean arterial pressure was elevated, but arterial pulse pressure and heart rate did not alter. At 70 degrees HUT with LBPP, the enhanced MSNA response was reduced (33.8 +/- 5.0 vs. 22.5 +/- 2.2 bursts/min, without vs. with LBPP; P < 0.05), mean arterial pressure was higher, the decreased pulse pressure was restored, and the increased heart rate was attenuated. We conclude that the baroreflex-mediated enhancement in sympathetic activity during HUT was reduced by LBPP. Application of LBPP in HUT induced an obvious cephalad fluid shift as well as a restoration of arterial pulse pressure, which reduced the inhibition of the baroreceptors. However, the activation of the intramuscular mechanoreflexes produced by 30 mmHg LBPP might counteract the effects of baroreflexes.