Histological analysis of the aortic nerve in the rat raised in space (Rapid communication on Neurolab Project).

To study development of the aortic nerve baroreflex under conditions of microgravity, we examined the cross section of the left aortic nerve (LAN), which is the afferent of the baroreflex, in the neonate rats aged 25 days raised in microgravity on the space shuttle Columbia (flight:FLT group) for 16 days. In this paper, we report a part of the result obtained from the data of the myelinated fibers of LAN analyzed with an electron microscope. Two kind of ground control groups were compared to the FLT group; one was asynchronous ground control (AGC) group where the rats were housed in the same cage as that on the shuttle, and the other was vivarium(VIV) group where the rats were housed in a commercial cage. The LANs in each group were extirpated the from rats perfused with a fixative and embedded for histological analysis. We observed the transverse sections of LAN and took pictures of several areas (magnified to x 2K to x 200K). No irregular myelination was found in all fibers of FLT group when they were compared with two control groups. The thickness of myelin of the maximally myelinated fibers were 0.55 +/- 0.17 micrometer in FLT(n=5), 0.45 +/- 0.10 micrometer in AGC(n=5), and O.47 +/- 0.06 micrometer meter in VIV(n=5). There was no significant difference among three groups (unpared t-test). The results suggest that there is no effect of space environment on the myelin formation of each nerve fiber in the aortic nerve.     

Effects of space flight on the histological characteristics of the aortic depressor nerve in the adult rat: electron microscopic analysis.

The effects of microgravity on the histological characteristics of the aortic depressor nerve, which is the afferent of the aortic baroreflex arc, were determined in 10 female adult rats. The rats were assigned for nursing neonates in the Space Shuttle Columbia or in the animal facility on the ground (NASA Neurolab, STS-90), and were housed for 16 days under microgravity in space (microg, n=5) or under one force of gravity on Earth (one-g, n=5). In the Schwann cell unit in which the axons of unmyelinated fibers are surrounded by one Schwann cell, the average number of axons per unit in the microg group was 2.1 +/- 1.6 (mean +/- SD, n=312) and significantly less than that in the one-g group (3.0 +/- 2.9, n=397, p<0.05). The proportion of unmyelinated fibers in the aortic depressor nerve in the microg group was 64.5 +/- 4.4% and significantly less than that in the one-g group (74.0 +/- 7.3%, p<0.05). These results show that there is a decrease in the number of high-threshold unmyelinated fibers in the aortic depressor nerve in adult rats flown on the Shuttle Orbiter, suggesting that the aortic baroreflex is depressed under microgravity during space flight.     

Structural and functional characteristics of the aortic nerve in the rabbit raised in head-down tilt posture

When human returns to the earth from space, the reverse shift of body fluid to the shift caused by microgravity. The physical phenomenon produces probably cardiovascular deconditioning due to a disturbance of the baroreflex for regulating blood pressure. To clarify the disturbance, the nervous control mechanisms of cardiovascular system in mammals exposed to microgravity should be investigated. Head-down tilt (HDT) is one of the methods to simulate the headward shift of the body fluid. To understand the effect of microgravity on the cardiovascular nervous control system, we studied effects of headward shift of the body fluid on structural and functional development of the aortic nerve and the aortic baroreflex in the young rabbit raised in a head-down and tail-up posture.     

Effects of microgravity on organ development of the neonatal rat.

We analyzed various organs in the same rats to study effects of gravitational condition on organ development of the neonatal rat in this study. Eight-day old and 14-day old Sprague-Dawley rats were flown for 16 days on the Space Shuttle Columbia (April 17-May 3, 1998). The organs were weighed and the ratio of the organ weight to the body weight (organ weight ratio; OBR) was calculated. Tissues were analyzed using anatomical, immunohistochemical and molecular biological technique. Six animals of the 8-day old group were reared on the ground for 30 more days after landing. The differences between flight and control rats in 8-day group were drastic. The lung, heart, kidney and adrenal glands in flight rats were significantly larger than that of control rats in OBR comparison. However, only the lung and kidney were still larger after 30 more days on ground. The kidney in flight rats performed pelvis expansion with down-regulation of aquaporin-2 expression confirmed by immunohistochemistry. The thymus, spleen, mesentery and pancreas were smaller in OBR. But the thymus in flight rats was heavier after 30 more days. The organs in flight rats which had no differences in OBR showed normal characteristics in histological analysis. We also found that the number of unmyelinated fibers of the aortic nerve in flight rats of 8-day group was smaller than that in control rats. In flight rats of the 14-day group, only the kidney was heavier and the ovary was lighter as compared to the controls. These results implied the second week of life was important for development during spaceflight. And the sensitivity and the critical period on neonatal development under microgravity might differ in each organ.     

Mechanical tensile properties of the aortic wall in the premature rat exposed to the microgravity environment during space flight for 16 days

Under microgravity environment, blood shifts headward and thereafter decrease in volume to adapt to the environment, which could affect cardiovascular hemodynamics and their regulatory mechanisms. Baroreceptor sensitivity is known to be reduced in newborn animals and to gradually increase with development. The baroreceptor is a stretch receptor; therefore its function is closely related to the rheological properties and fine structure of the aortic wall in which the baroreceptor lies. The mechanical and histological properties could be altered under microgravity conditions in the process of development with change in circulatory function. In the present study, we investigated the mechanical tensile characteristics and histological structure of the aortic wall in the proximal thoracic aorta of premature rats bred in the microgravity environment of the space shuttle for 16 days.     

Effects of the spaceflight on organ-development in the neonatal rats: results in the Neurolab (STS-90)]

In the Neurolab mission, we found that spaceflight affects the development of the aortic baroreflex system and the body weight of the flight rats was significantly lighter [correction of lightess] than that of the control group. The aim of this study is to examine the structural and functional development in various tissues and organs. One hundred and eighteen nine-day old rats and seven fifteen-day old rats, which were launched at these ages and nursed by their dams in the space shuttle Columbia for 16 days, were served for this study. Two hundred and twenty one neonates were used as the ground controls (VIV: vivarium and AGC: asynchronous ground controls). On the landing day after they returned to the earth, the rats were perfused with a fixative under deep urethane anesthesia, and the organs were weighed and the ratio of the organ weight to the body weight was calculated. Six animals of the nine-day old group were reared on the ground for 30 more days after landing and also examined in the same protocol as the landing-day-examination. The organs obtained to examine were heart, lung, spleen, thymus, adrenal glands, kidney, liver, small intestine, large intestine, mesentery, pancreas, testis and ovary. Paraffin sections were made from some organ tissues and prepared for HE staining and immunohistochemistry. We compared these organs in the flight rat with those in the ground controls. All organs except the lung of nine-day old group were significantly smaller. In the ratio of organ weight to body weight, the lung and heart were significantly larger. The weight and ratio of the liver showed no significant difference. The thymus, spleen, mesentery and pancreas were smaller in the weight and the ratio. There were no differences in the body weight among 30-day reared groups, but the lung in the flight group is significantly heavier than the control groups and thymus also tends to be relatively heavy. In flight rats of the fifteen-day group, the kidney was heavy and the ovary was light as compared to the controls. The adipose tissue was macroscopically little found around the thoracic and abdominal organs in all rats of the flight group. These results suggest that the organs related to oxygen supply like as the lung and heart have priority in development over the mesentery and immune system organs even during spaceflight. Lightness of the mesentery in space rats is due to small contents of adipose tissues, and may reflect amounts of the food taken by the flight dams. Lightness of the organs like as the thymus, spleen and pancreas suggests that spaceflight may affect the immune system and also affect continuously the lung and thymus development even after landing.     

Skeletal muscle adaptations to microgravity exposure in the mouse.

To investigate the effects of microgravity on murine skeletal muscle fiber size, muscle contractile protein, and enzymatic activity, female C57BL/6J mice, aged 64 days, were divided into animal enclosure module (AEM) ground control and spaceflight (SF) treatment groups. SF animals were flown on the space shuttle Endeavour (STS-108/UF-1) and subjected to approximately 11 days and 19 h of microgravity. Immunohistochemical analysis of muscle fiber cross-sectional area revealed that, in each of the muscles analyzed, mean muscle fiber cross-sectional area was significantly reduced (P < 0.0001) for all fiber types for SF vs. AEM control. In the soleus, immunohistochemical analysis of myosin heavy chain (MHC) isoform expression revealed a significant increase in the percentage of muscle fibers expressing MHC IIx and MHC IIb (P < 0.05). For the gastrocnemius and plantaris, no significant changes in MHC isoform expression were observed. For the muscles analyzed, no alterations in MHC I or MHC IIa protein expression were observed. Enzymatic analysis of the gastrocnemius revealed a significant decrease in citrate synthase activity in SF vs. AEM control.     

A model for studying the baroreflex in microgravity and hypergravity

The study on development in altered gravity has been investigated in a wide range of animal species from a molecular level or cell culture to mammalian bodies. However development of the baroreflex has been studied in limited mammalian species even on the ground except the turtle to study diving reflex. The rat or mouse has been selectively used for studying the relationship between development of various functions and gravity especially microgravity, because of the limited body size for the loading space on the space ship, an experimental-animal most often used, and other biological characteristics. We have used the rat and rabbit for investigating the effect of microgravity on the development of the aortic baroflex. In the present paper a few results of our experiments using the rat will be shown and the appropriateness of the rat as a model system for studying the baroflex development in altered gravity will be discussed.     

alpha(2)-Adrenergic receptors in NTS facilitate baroreflex function in adult spontaneously hypertensive rats

We examined the effect of alpha(2)-adrenoreceptor blockade in the nucleus of the solitary tract (NTS) on baroreflex responses elicited by electrical stimulation of the left aortic depressor nerve (ADN) in urethane-anesthetized spontaneously hypertensive rats (SHR, n = 11) and normotensive Wistar-Kyoto rats (WKY, n = 11). ADN stimulation produced a frequency-dependent decrease in mean arterial pressure (MAP), renal sympathetic nerve activity (RSNA), and heart rate (HR). In SHR, unilateral microinjection of idazoxan into the NTS markedly reduced baroreflex control of MAP, RSNA, and HR and had a disproportionately greater influence on baroreflex control of MAP than of RSNA. In WKY, idazoxan microinjections did not significantly alter baroreflex function relative to control vehicle injections. These results suggest that baroreflex regulation of arterial pressure in SHR is highly dependent on NTS adrenergic mechanisms. The reflex regulation of sympathetic outflow to the kidney is less influenced by the altered alpha(2)-adrenoreceptor mechanisms in SHR.     

Effects of cage beddings on microsomal oxidative enzymes in rat liver

The purpose of the present studies was to evaluate the effects of some commercially available cage beddings on rat liver microsomal cytochrome P-450-dependent drug-metabolizing enzyme, ethylmorphine N-demethylase, and the carcinogen-metabolizing enzyme, benzo(a)pyrene hydroxylase. Sprague-Dawley rats were housed in cages containing cedar chip, corncob or heat-treated pinewood bedding for 3 weeks. Control rats were housed in cages on wire bottom floors containing no bedding material. Rats housed in cages containing cedar chip showed 18, 46 and 49% increases in liver cytochrome P-450 content, ethylmorphine N-demethylase and benzo(a)pyrene hydroxylase activities, respectively. The liver enzyme activities of rats housed in cages containing corncob bedding were similar to those obtained with control rats. In contrast, the pinewood-bedded rats showed a 21% decrease in ethylmorphine N-demethylase activity without affecting cytochrome P-450 content and benzo(a)pyrene hydroxylase activity. Hexobarbital-induced sleep times of the variously bedded rats were similar to those of control animals. These data suggest that the commercial bedding materials differ in their abilities to affect liver microsomal enzymes. Thus, interlaboratory variability in basal enzyme activities reported in the literature may be partly due to bedding materials used in the animal's cages.     

Effect of blockade of endogenous angiotensin II on baroreflex function in conscious diabetic rats

Little is known about baroreflex control of renal nerve sympathetic activity (RSNA) or the effect of angiotensin II (ANG II) on the baroreflex in diabetes. We examined baroreflex control of RSNA and heart rate (HR) in conscious, chronically instrumented rats 2 wk after citrate vehicle (normal) or 55 mg/kg iv streptozotocin (diabetic) before and after losartan (5 mg/kg iv) or enalapril (2.5 mg/kg iv). Resting HR and RSNA were lower in diabetic versus normal rats. The range of baroreflex control of HR and the gain of baroreflex-mediated bradycardia were impaired in diabetic rats. Maximum gain was unchanged. The baroreflex control of RSNA was reset to lower pressures in the diabetic rats but remained otherwise unchanged. Losartan decreased mean arterial pressure (MAP) and increased HR and RSNA in both groups but had no influence on the baroreflex. Enalapril decreased MAP only in normal rats, yet the increase in HR and RSNA was similar in both groups. Thus in diabetic rats enalapril produced a pressure-independent increase in HR and RSNA. Enalapril exerted no effect on the baroreflex control of HR or RSNA in either group. These data indicate that in conscious rats resting RSNA is lower but baroreflex control of RSNA is preserved after 2 wk of diabetes. At this time, the baroreflex control of HR is already impaired and blockade of endogenous ANG II does not improve this dysfunction.     

Electrophysiological and neuroanatomical evidence of sexual dimorphism in aortic baroreceptor and vagal afferents in rat

Evidence for sexual dimorphism in autonomic control of cardiovascular function is both compelling and confounding. Across healthy and disease populations sex-associated differences in neurocirculatory hemodynamics are far too complex to be entirely related to sex hormones. As an initial step toward identifying additional physiological mechanisms, we investigated whether there is a sex bias in the relative expression of low-threshold-myelinated and high-threshold-unmyelinated aortic baroreceptor afferents in rats. These two types of afferent fibers have markedly different reflexogenic effects upon heart rate and blood pressure and thus the potential impact upon baroreflex dynamics could be substantial. Our results, using a combination of a patch-clamp study of fluorescently identified aortic baroreceptor neurons (ABN) and morphometric analysis of aortic baroreceptor nerve fibers, demonstrate that females exhibit a greater percentage of myelinated baroreceptor fibers (24.8% vs. 18.7% of total baroreceptor fiber population, P < 0.01) and express a functional subtype of myelinated ABN rarely found in age-matched males (11% vs. 2.3%, n = 107, P < 0.01). Interestingly, this neuronal phenotype is more prevalent in the general population of female vagal afferent neurons (17.7% vs. 3.8%, n = 169, P < 0.01), and ovariectomy does not alter its expression but does lessen neuronal excitability. These data suggest there are fundamental neuroanatomical and electrophysiological differences between aortic baroreceptor afferents of female and male rats. Possible explanations are presented as to how such a greater prevalence of low-threshold myelinated afferents could be a contributing factor to the altered baroreflex sensitivity and vagal tone of females compared with males.     

Hindlimb unloading and female gender attenuate baroreflex-mediated sympathoexcitation

Exposure to a period of microgravity or bed rest produces several physiological adaptations. These changes, which include an increased incidence of orthostatic intolerance, have an impact when people return to a 1G environment or resume an upright posture. Compared with males, females appear more susceptible to orthostatic intolerance after exposure to real or simulated microgravity. Decreased arterial baroreflex compensation may contribute to orthostatic intolerance. We hypothesized that female rats would exhibit a greater reduction in arterial baroreflex function after hindlimb unloading (HU) compared with male rats. Mean arterial pressure (MAP), heart rate (HR), and renal sympathetic nerve activity (RSNA) were recorded in conscious animals after 13-15 days of HU. Baseline HR was elevated in female rats, and HU increased HR in both genders. Consistent with previous results in males, baroreflex-mediated activation of RSNA was blunted by HU in both genders. Maximum RSNA in response to decreases in MAP was reduced by HU (male control 513 +/- 42%, n = 11; male HU 346 +/- 38%, n = 13; female control 359 +/- 44%, n = 10; female HU 260 +/- 43%, n = 10). Maximum baroreflex increase in RSNA was lower in females compared with males in both control and HU rats. Both female gender and HU attenuated baroreflex-mediated increases in sympathetic activity. The combined effects of HU and gender resulted in reduced baroreflex sympathetic reserve in females compared with males and could contribute to the greater incidence of orthostatic intolerance in females after exposure to spaceflight or bed rest.     

Variable lymphocyte responses in rats after space flight.

Most studies of human blood lymphocyte function following space flight have indicated that microgravity suppresses T cell proliferation. However, several other postflight experiments with animals have shown no decrease in proliferation of lymphocytes from peripheral lymphatic tissues, suggesting that different tissues may be variably affected by microgravity. Therefore, we examined the proliferation of lymphocytes from both spleen and lymph nodes of rats following a 4-day flight aboard the Space Shuttle. The experiments were designed to investigate tissue variability as well as potential mechanisms involved in suppressing proliferation. We found that proliferation of lymph node lymphocytes (LNL) from flight (FLT) animals stimulated with the antigen receptor-dependent T cell mitogen concanavalin A was depressed and could not be restored by supplementing cultures with interleukin 1 or interleukin 2 (IL-2). Response to another receptor-dependent mitogen, phytohemagglutinin, was not decreased. However, proliferation of FLT LNL following stimulation with the receptor-independent, mitogenic combination of phorbol ester and ionomycin was depressed. LNL IL-2 activity, cell surface marker expression, and B cell responses to mitogen were normal. Thus, deficits in antigen receptor/ligand interactions, cell surface marker expression, or IL-2 did not account for the suppressed lymphocyte proliferation observed postflight. In contrast to LNL, FLT splenocyte proliferation was not depressed. Assayable IL-2, IL-2 receptor expression, and cell surface marker expression likewise were unaffected by space flight. The differences between lymph node and splenic responses demonstrate the tissue-specific nature of microgravity effects on individual lymphatic tissues.     

Effects of wire-bottom caging on heart rate, activity and body temperature in telemetry-implanted rats

Some experimental procedures are associated with placement of animals in wire-bottom cages. The goal of this study was to evaluate stress-related physiological parameters (heart rate [HR], body temperature [BT], locomotor activity [LA], body weight [BW] and food consumption) in rats under two housing conditions, namely in wire-bottom cages and in bedding-bottom cages. Telemetry devices were surgically implanted in male Sprague-Dawley rats. HR, BT and LA were recorded at 5 min intervals. Analysis under each housing condition was performed from 16:00 to 08:00 h of the following day (4 h light, 12 h dark). During almost all of the light phase, the HR of rats housed in wire-bottom cages remained high (371 ± 35 bpm; mean ± SD; n = 6) and was significantly different from that of rats housed in bedding-bottom cages (340 ± 29 bpm; n = 6; P < 0.001; Student's t-test). In general, BT was similar under the two housing conditions. However, when rats were in wire-bottom cages, BT tended to fluctuate more widely during the dark phase. LA decreased when animals were housed in wire-bottom cages, in particular during the dark phase. Moreover, there was a significant difference with respect to the gain in BW: BW of rats housed in bedding-bottom cages increased 12 ± 2 g, whereas that of rats in wire-bottom cages decreased by 2 ± 3 g (P < 0.001). Our results demonstrate that housing rats in wire-bottom cages overnight leads to immediate alterations of HR, BW and LA, which might be related to a stress response.     

Microarray analysis of spaceflown murine thymus tissue reveals changes in gene expression regulating stress and glucocorticoid receptors

The detrimental effects of spaceflight and simulated microgravity on the immune system have been extensively documented. We report here microarray gene expression analysis, in concert with quantitative RT‐PCR, in young adult C57BL/6NTac mice at 8 weeks of age after exposure to spaceflight aboard the space shuttle (STS‐118) for a period of 13 days. Upon conclusion of the mission, thymus lobes were extracted from space flown mice (FLT) as well as age‐ and sex‐matched ground control mice similarly housed in animal enclosure modules (AEM). mRNA was extracted and an automated array analysis for gene expression was performed. Examination of the microarray data revealed 970 individual probes that had a 1.5‐fold or greater change. When these data were averaged (n = 4), we identified 12 genes that were significantly up‐ or down‐regulated by at least 1.5‐fold after spaceflight (P ≤ 0.05). The genes that significantly differed from the AEM controls and that were also confirmed via QRT‐PCR were as follows: Rbm3 (up‐regulated) and Hsph110, Hsp90aa1, Cxcl10, Stip1, Fkbp4 (down‐regulated). QRT‐PCR confirmed the microarray results and demonstrated additional gene expression alteration in other T cell related genes, including: Ctla‐4, IFN‐α2a (up‐regulated) and CD44 (down‐regulated). Together, these data demonstrate that spaceflight induces significant changes in the thymic mRNA expression of genes that regulate stress, glucocorticoid receptor metabolism, and T cell signaling activity. These data explain, in part, the reported systemic compromise of the immune system after exposure to the microgravity of space. J. Cell. Biochem. 110: 372–381, 2010. © 2010 Wiley‐Liss, Inc.     

家兔主动脉神经低阈压力感受反射快速重调中枢过程的特征

40只家兔,乌拉坦静脉麻醉。切断双侧主动脉神经(AN)、窦神经及迷走神经。以选择兴奋 AN 有髓传人纤维的条件刺激(0.02ms,50Hz,4—6V,5min)给予切断的 AN 中枢段,模拟导致低阈压力感受反射快速重调的保持压背景,借以诱导快速重调的中枢过程。实验表明:该中枢过程使 AN 有髓纤维传入所激发的压力感受反射降压效应衰减41.82%(P<0.01),肾交感神经活动抑制效应衰减19.31%(P相似文献   

Lack of effect of spaceflight on bone mass and bone formation in group-housed rats

As part ofan experiment to study the role of corticosteroids in bone changesduring spaceflight, male Sprague-Dawley rats (6 wk old, 165 g bodyweight) were placed in orbit for 17 days, in groups of six, inanimal-enclosure modules (AEMs) aboard the space shuttle Columbia(STS-78). Control rats were group housed in a similar manner inground-based AEMs or standard vivarium cages. Adrenal hypertrophyoccurred in flight rats, but bone histomorphometric analyses revealed alack of significant changes in bone mass and bone formation in theseanimals. Cancellous bone volume and osteoblast surface in the proximaltibial metaphysis were nearly the same in flight and ground-based rats.Normal levels of cancellous bone mass and bone formation were alsodetected in the lumbar vertebrae and femoral necks of flight rats. Inthe tibial diaphysis, periosteal bone formation rate was found to beidentical in flight and ground-based rats. The results indicate that,under conditions of group housing in AEMs, spaceflight has minimaleffects on bone mass and bone formation in rapidly growingrats. These findings emphasize the need to investigate theimportance of rat age, strain, and especially housing conditions forstudies of the skeletal effects of spaceflight.

     

State of Brassica rapa photosynthetic membranes in microgravity

The structural characteristics of the photosynthetic apparatus of Brassica rapa plants grown on board the space shuttle Columbia (STS-87) for 15 days were examined using the methods of transmission electron microscopy and statistic programme STAT. Maintaining of the same growth conditions for control plants was realized with great accuracy using the Orbiter Environmental simulator in Kennedy Space Center. A grana number per a medial section 1.8 times decreased in microgravity. Considerable changes were also revealed in the grana structure in microgravity in comparison with th ground control, namely: 1/a greater diversity in the thylakoid length with granae and 2/ lateral shifting of the thylakoids lateral shifting of the thylakoids relative one to another. The previous mentioned pheomenon was found for 64% of the invested granae. Shifting of the thylakoids in the granae in microgravity led to increasing of the grana thylakoid surface exposed to a stroma. In addition, the volume of stromal thylakoids increased. The peculiarities in the photosynthetic apparatus structure in microgravity are supposed to be an evidence of decreasing in the light harvesting complex amount of photosystem II (PSII).     

2-D DIGE and MS/MS analysis of protein serum expression in rats housed in concrete and clay cages in winter

In a previous study, we examined the physiological responses of male Sprague-Dawley rats over a 4-week exposure to concrete and clay cages. No general toxicological changes were observed in rats exposed to either of the two cage types in summer. Under winter conditions, however, various general toxicological effects were detected in rats housed in concrete cages, although rats housed in clay cages showed no such effects. The infrared thermographic examination indicated that skin temperature in the concrete-housed rats was abnormally low, but not so in the clay-housed rats. We examined proteomic changes in the serum of rats housed in winter in concrete and clay cages using two-dimensional differential in-gel electrophoresis and mass spectrometry/mass spectrometry. Five proteins were identified and quantitatively validated; all were cold stress-induced, acute phase proteins that were either up-regulated (haptoglobin) or down-regulated (alpha-1-inhibitor III, alpha-2u globulin, complement component 3, and vitamin D-binding protein) in the concrete-housed rats. These results suggest that the 4-week exposure to a concrete cage in winter elicited a typical systemic inflammatory reaction (i.e. acute phase response) in the exposed rats.