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 microm(2) 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.

Choroidal readaptation to gravity in rats after spaceflight and head-down tilt.

To determine when choroidal structures were restored after readaptation to Earth gravity or orthostatic position, fine structure and protein distribution were studied in rat choroid plexus dissected either 6 h [Space Life Sciences-2 (SLS-2) experiments] or 2 days [National Institutes of Health-Rodent 1 (NIH-R1) experiments] after a spaceflight, or 6 h after head-down tilt (HDT) experiments. Apical alterations were noted in choroidal cells from SLS-2 and HDT animals, confirming that weightlessness impaired choroidal structures and functions. However, the presence of small apical microvilli and kinocilia and the absence of vesicle accumulations showed that the apical organization began to be restored rapidly after landing. Very enlarged apical microvilli appeared after 2 days on Earth, suggesting increased choroidal activity. However, as distributions of ezrin and carbonic anhydrase II remained altered in both flight and suspended animals after readaptation to Earth gravity, it was concluded that choroidal structures and functions were not completely restored, even after 2 days in Earth's gravity.

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.

Changes in apical organization of choroidal cells in rats adapted to spaceflight or head-down tilt.

Structural changes observed in choroid plexuses from rats dissected aboard a space shuttle, on day 13 of an orbital flight (NASA STS-58 mission, SLS-2 Experiments) demonstrated that choroidal epithelial cells display a modified organization in a microgravitational environment. Results were compared with ultrastructural observations of choroid plexus from rats maintained under anti-orthostatic restraint (head-down tilt) for 14 days. In both experiment types, the main alterations observed by transmission electron microscopy, at the level of choroidal epithelial cells from the third and fourth ventricles, concerned the formation and the organization of apical microvilli, whereas pseudopod-like structures appeared. Immunocytochemical distribution of ezrin, a cytoskeletal protein involved in apical cell differentiation in choroid plexus, confirmed the structural alteration of microvilli in head-down tilted rats, Kinocilia tended to disappear from the apical surface, suggesting a partial loss of cell polarization. In addition, large amounts of clear vesicles were gathered in the apical cytoplasm of choroidal epithelial cells. Disorganization of apical microvilli accumulations of apical vesicles and partial loss of cell polarity showed that long-stays in weightlessness induced alterations in the fine structure of choroid plexus, consistent with a marked reduction of cerebrospinal fluid production.

Myonuclear number and myosin heavy chain expression in rat soleus single muscle fibers after spaceflight.

The effects of 14 days of spaceflight on myonuclear number, fiber size, and myosin heavy chain (MHC) expression in isolated rat soleus muscle fiber segments were studied. Single soleus muscle fibers from rats flown on the Spacelab Life Sciences-2 14-day mission were compared with those from age-matched ground-based control rats by using confocal microscopy and gel electrophoresis. Spaceflight resulted in a significant reduction in the number of fibers expressing type I MHC and an increase in the number of fibers expressing type IIx or IIa MHC. Space-flight also resulted in an increase in the percentage of fibers coexpressing more than one MHC and in the reexpression of the neonatal isoform of MHC in some fibers. Fiber cross-sectional area was significantly reduced in pure type I MHC-expressing fibers and in fibers coexpressing type I+II MHC but not in fibers expressing one or more type II MHC in the flight rats. The number of myonuclei per millimeter was significantly reduced in type I MHC-expressing fibers from the flight rats but was not significantly different in type I+II and type II MHC-coexpressing fibers. Fibers expressing neonatal MHC were similar in size to control fibers but had significantly fewer myonuclei per millimeter than flight fibers not expressing neonatal MHC. In type I MHC-expressing fibers, the reduction in fiber cross-sectional area was greater than the reduction in myonuclear number; thus the average cytoplasmic volume per myonucleus was significantly lower in flight than in control fibers. The reduction in both myonuclear number and fiber size of fibers expressing type I MHC after 14 days of spaceflight supports the hypothesis that changes in the number of myonuclei may be a contributing factor to the reduction in fiber size associated with chronic unloading of the musculature.

Spaceflight effects on beta-adrenoceptor and metabolic properties in rat plantaris.

Effects of 14 days of spaceflight on beta-adrenoceptor (beta-AR), mitochondrial enzyme activities, and fiber type composition were studied in plantaris muscles of male adult Sprague-Dawley rats. The beta-AR was analyzed in cross sections by quantitative autoradiography. The maximum binding capacity (Bmax) of beta-AR was significantly lowered (approximately 29%) after flight, but the recovery was not completed within 9 days in 1-G environment. Because the dissociation constant remained unchanged, it is suggested that the changes in the Bmax were caused by the alteration of receptor number. The activities of succinate dehydrogenase (SDH) measured in whole homogenates were subnormal (approximately -24%) in muscles sampled approximately 5 h after flight but they were normalized during 9 days of recovery. The percent composition of fiber types and beta-hydroxyacyl CoA dehydrogenase (HAD) activity did not change significantly due to spaceflight. It is suggested that the spaceflight-induced decrease of the Bmax of beta-AR in plantaris was accompanied by a lowered activity of a mitochondrial inner-membrane enzyme SDH but not a matrix enzyme HAD.

[Experimental morphological studies of stress-inducing effects of weightlessness in rats flown aboard Spacelab-2]. / Eksperimental'no-morfologicheskoe issledovanie stressogennykh éffektov nevesomosti u krys, éksponirovannykh na "Speisléb-2".

Adrenals and thymus of rats flown for 14 days on board the US space life sciences laboratory, Spacelab-2 (SLS-2), were analyzed histologically and histomorphometrically. Adrenals of the rats sacrificed on flight day 13 did not exhibit any morphological signs of elevated functional activity. Within 5 hours following the mission, the functioning of adrenals was growing, while thymus displayed sites of thymocyte histolysis and suppression of cell mitotic activity. Taken together, these observations infer the development of stress. Based on the morphological criteria, a conclusion has been drawn that the exposure on board SLS-2 did not exert any expressed stress-inducing effect on the rats and it was the transfer from microgravity to the normal gravity that produced acute gravitational stress of moderate severity.

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.

The effect of respirator dead space and lung retention on exposure estimates.

This paper develops, tests, and applies equations that predict the magnitude of the effect of lung retention and respirator dead space on average inhalation concentration and other related quantities. The equations were validated by numerical simulation and experimental measurement with a respirator on a mannequin connected to a breathing machine. Experimental data are presented verifying the applicability of the equations. The authors present applications of the equations and procedures to various types of respirator performance measurements and to a predictive respirator performance model. Graphs are presented giving correction factors. In all cases the correction factors are less than 2. Under typical conditions of workplace protection factor measurement with half-mask respirators, average inhalation concentration will be 105% to 125% of full-cycle average concentration.

Distribution, propagation, and coordination of contractile activity in lymphatics.

The propagation and coordination of lymphatic contractions were studied in the mesentery of the rat small intestine using in situ microscopic observation. Indexes of lymphatic diameter were simultaneously measured at two adjacent lymphangions in spontaneously contracting lymphatics (n = 51). Diameter index, contraction frequency, and the percentage of the intersegmental contractions that were propagated and coordinated (PP) were determined at both sites. The conduction velocity of the contractile activity and the percentage of the coordinated contractions that were propagated both antegrade to the direction of lymph flow and retrograde to the flow stream were determined. The results indicate that 1) 80-90% of the lymphatic contractions in the vessels we evaluated were propagated, 2) the wave of contractile activity propagated both centrally and peripherally, and 3) the conduction velocity of the contractile activity was approximately 4-8 mm/s. We tested the hypothesis that gap junctional communication is responsible for the coordination of the contractile event. To accomplish this, we used the gap junction blockers n-heptanol and oleic acid. PP was 90 +/- 4% under normal conditions and fell to a minimum value of 55 +/- 7% during the gap junction blockade. These results indicate that gap junctional communication played an important role in the propagation and coordination of contractions that occurred in spontaneously active lymphatics.

Reactive oxygen metabolites inhibit spontaneous lymphatic contractions.

The effects of oxygen-derived free radicals on the contractile activity of the mesenteric collecting lymphatics were evaluated in the anesthetized rat. Lymphatic contractions were monitored before, during and after the application of oxyradicals. Contraction frequency (F), stroke volume (SV), ejection fraction (EF), contraction propagation (PC), and lymph pump flow (LPF) were determined from the lymphatic diameter tracings. Oxyradicals were generated using hypoxanthine and xanthine oxidase. Exposure to oxyradicals inhibited the lymphatic pumping mechanism: 1) F fell from 15.5 +/- 0.8 to 0.8 +/- 0.7 beats/min; 2) EF went from 0.44 +/- 0.02 to 0.08 +/- 0.04; 3) PC dropped from 92 +/- 2 to 56 +/- 8%; and 4) LPF fell precipitously from 41.0 +/- 5.2 to 0.7 +/- 0.4 nl/min. The effects of the oxyradicals were attenuated by superoxide dismutase, implicating superoxide anion as one of the predominant causative agents. We conclude that oxyradicals significantly inhibit the lymph pump and that this inhibition could be a factor contributing to the formation of interstitial edema during inflammation.

The role of industrial hygiene in preventing occupational lung disease.

This chapter examines the role of industrial hygienists in preventing pulmonary disease. As part of a team, these environmental specialists are trained to anticipate, recognize, evaluate, and control environmental health hazards in the workplace. Lung diseases, caused by exposure to airborne chemicals in the form of dusts, mists, gases, and vapors, are among the most serious health hazards facing industrial workers and consequently are an important consideration for industrial hygienists.

Aerosol penetration through respirator exhalation valves.

Exhalation valves are a critical component of industrial respirators. They are designed to permit minimal inward leakage of air contaminants during inhalation and provide low resistance during exhalation. Under normal conditions, penetration of aerosol through exhalation valves is minimal. The exhalation valve is, however, a vulnerable component of a respirator and under actual working conditions may become dirty or damaged to the point of causing significant leakage. Aerosol penetration was measured for normal exhalation valves and valves compromised by paint or fine copper wires on the valve seat. Penetration increased with increasing wire diameter. A wire 250 microns in diameter allowed greater than 1% penetration into the mask cavity. Dirt or paint accumulated on the exhalation valve allowed a similar level of penetration. Work rate had little effect on observed penetration. Penetration decreased significantly with increasing aerosol particle size. The amount of material on the valve or valve seat necessary for significant (greater than 0.5%) inward leakage in a half-mask respirator could be readily observed by careful inspection of the exhalation valve and its seat in good lighting conditions.

Goal setting, social support, and financial incentives in stress management programs: a pilot study of their impact on adherence.

Abstract A stress management program was implemented at two worksites to answer the following questions: 1) Is it feasible to design a stress management program that is of sufficient duration to change old habits, is tailored to the specific needs of the individual, and yet is administratively manageable? 2) To what degree does the use of powerful, reliable, independent variables make it possible for program participants to adhere to a stress management goal of their choosing? A program of six months duration that included personal stress management projects attracted a total of 21 participants at the two worksites. They met their weekly personal project commitments more than 80 percent of the time, and significant changes occurred on a measure of social anxiety.

Detection of antibodies to Herpesvirus saimiri late antigens in human sera.

One hundred fifty sera from handlers of squirrel monkeys and 100 sera from individuals who had never handled monkeys were tested by immunofluorescence for antibodies reactive to structural proteins of Herpesvirus saimiri (HVS). Eleven (7.3%) of the occupationally exposed group and 4 (4%) of the noncontact group were seropositive for HVS by immunofluorescence assay, and 10 of these 15 (6.7 and 2%, respectively) were also seropositive for either the major glycoprotein (140 kD) or the major capsid protein (160 kD) of HVS by radioimmunoprecipitation assay. Two sera from handlers of squirrel monkeys, however, recognized many different HVS structural antigens by immunoprecipitation, and it seems unlikely that they could also be cross-reactive antibodies. Since these two sera did not contain antibodies to HVS early antigens or to the nonstructural antigens present in infected owl monkey kidney cells, and follow-up sera collected from the same individuals several months later were negative for antibodies to HVS, these individuals do not appear to have been infected by the virus. The risk that HVS poses to humans appears to be very low.

Performance of dust respirators with facial seal leaks: I. Experimental.

The ability of representative half-mask and single-use respirators with facial seal leaks to provide protection against aerosols was evaluated by experimental measurement. Respirators were mounted on a manikin in a test chamber and operated at seven steady flow rates over the range of 2 to 150 L/min. Samples of polydisperse and monodisperse aerosols were taken from inside and outside the respirator and analyzed by a calibrated optical particle counter over the particle-size range 0.1 to 11.3 microns. Measurements were made separately for filter performance as a function of particle size and flow rate, and simulated leak performance (penetration) as a function of particle size, pressure drop, and leak size. Flow rate vs. pressure drop measurements were made for all filters and leaks tested. For a given leak condition the percentage of the total flow traversing the leak varied several fold over the usual range of airflow rates through a respirator. Aerosol penetration was found to depend strongly on particle size and flow rate for filters, and to depend strongly on particle size and less strongly on pressure drop for leaks. One can conclude from these measurements that the aerosol-size distribution inside a respirator will nearly always be significantly different from that outside the respirator.

Performance of dust respirators with facial seal leaks: II. Predictive model.

A performance model for half-mask and single-use respirators is presented. It represents a possible alternative to field measurements of respirator performance. Experimental data on filter and leak performance given in Part I were used to develop a model that allows one to predict 1) the overall respirator penetration as a function of particle size for any work rate and 2) overall total mass penetration for any work rate and exposure aerosol-size distribution for a known respirator filter and facial seal leak condition. A simplified method based on general regression equations is presented that allows one to estimate these quantities based on QNFT (quantitative fit testing) measurements and a knowledge of the exposure aerosol-size distribution. Example calculations are given for a situation in which QNFT gives a fit factor of 50 for a half-mask with dust, fume and mist filter cartridges, but predicted protection factors for various use conditions range from 20 to 81 depending on exposure particle-size distribution and work rate of the wearer.