Role of AVP in mediating the altered core temperature response to a simulated open field in pregnant rats.

Near the term of pregnancy, rats have an attenuated core temperature response on exposure to a novel environment (e.g., a simulated open field) compared with that observed early in pregnancy or in nonpregnant rats. The present experiments were carried out on 26 nonpregnant and 26 pregnant rats to test the hypothesis that arginine vasopressin, functioning as an endogenous antipyretic substance in the central nervous system, mediates this attenuated core temperature response. Exposure to a simulated open field after intracerebroventricular (ICV) vehicle produced a significant increase in core temperature in both nonpregnant and pregnant animals, the magnitude and duration of which were greater in the nonpregnant rats. In nonpregnant rats, exposure to a simulated open field after ICV vasopressin V(1)-receptor antagonist altered the pattern of the core temperature response but not the core temperature index compared with that observed on exposure to a simulated open field after ICV vehicle. In pregnant animals, ICV vasopressin V(1)-receptor antagonist did not alter the core temperature response to a simulated open field compared with that observed after ICV vehicle. Thus our data do not support the hypothesis that a pregnancy-related activation of arginine vasopressin attenuates the core temperature response to a simulated open field in rats near the term of pregnancy.     

Pregnancy alters cardiac receptor afferent discharge in rats

Reflex effects of cardiac receptor (CR) stimulation are attenuated in pregnant rats. We tested whether CR afferent discharge is reduced during pregnancy by measuring single fiber activity in response to increases in right atrial pressure (RAP) in anesthetized pregnant and virgin rats with sinoaortic denervation. Single fiber activity was isolated from fine filaments of the right cervical vagus nerve. Changes in CR discharge, RAP, and arterial pressure were recorded in response to atrial saline injections (25-300 microl). Resting RAP was similar between groups, and spontaneous CR discharge was similar in pregnant rats (1.95+/-0.21 Hz) and in low-frequency (LF) receptors in virgin rats (1.30+/-0.2 Hz). In virgin, but not pregnant rats, a subset (24%) of CR had higher-frequency (HF) spontaneous discharge (9.91+/-1.19 Hz). During stimulation, the level of RAP above which CR firing increased was significantly higher in pregnant rats, but CR activity was clustered into an LF discharge range. Thus gestation appears to reduce the activity of CR afferents, possibly by increasing stimulus threshold or by selective inactivation of a subset of HF discharging receptors.     

N-acetylcysteine administration alters the response to inspiratory loading in oxygen-supplemented rats

Supinski, G. S., D. Stofan, R. Ciufo, and A. DiMarco.N-acetylcysteine administrationalters the response to inspiratory loading in oxygen-supplemented rats.J. Appl. Physiol. 82(4): 1119-1125, 1997.Based on recent studies, it has been suggested that free radicals are elaborated in the respiratory muscles during strenuous contractions and contribute to the development of muscle fatigue. If this theory is correct, then it should be possible toattenuate the development of diaphragm fatigue and/or delay theonset of respiratory failure during loaded breathing by administering afree radical scavenger. The purpose of the present experiment was,therefore, to examine the effect ofN-acetylcysteine (NAC), a free radicalscavenger and glutathione precursor, on the evolution of respiratoryfailure in decerebrate unanesthetized rats breathing against a largeinspiratory resistive load. We compared the inspiratory volume andpressure generation over time in animals pretreated with either salineor NAC (150 mg/kg) and then loaded until respiratory arrest. Afterarrest, the diaphragm was excised, and samples were assayed for reduced(GSH) and oxidized glutathione. As a control, we also assessedrespiratory function and glutathione concentrations in groups ofnonloaded saline- and NAC-treated animals. We found that NAC-treatedanimals were able to tolerate loading better than the saline-treatedgroup, maintaining higher inspiratory pressures and sustaining higherinspired volumes. Administration of NAC also increased the time thatanimals could tolerate loading before the development of respiratoryarrest. In addition, although saline-treated loaded animals hadsignificant reductions in diaphragmatic GSH levels compared withunloaded controls, the magnitude of this reduction was blunted by NACadministration (i.e., GSH averaged 965 ± 113, 568 ± 83, 907 ± 39, and 784 ± 61 nmol/g for unloaded-saline, loaded-saline,unloaded-NAC, and loaded-NAC groups, P < 0.05, with the value for the loaded-saline group lower than thevalues for the two unloaded groups; GSH for the loaded-NAC group was not different, however, from unloaded controls). These data demonstrate that administration of NAC, a free radical scavenger, slows the rate ofdevelopment of respiratory failure during inspiratory resistiveloading.

     

Fall field crickets did not acclimate to simulated seasonal changes in temperature

In nature, many organisms alter their developmental trajectory in response to environmental variation. However, studies of thermal acclimation have historically involved stable, unrealistic thermal treatments. In our study, we incorporated ecologically relevant treatments to examine the effects of environmental stochasticity on the thermal acclimation of the fall field cricket (Gryllus pennsylvanicus). We raised crickets for 5 weeks at either a constant temperature (25°C) or at one of three thermal regimes mimicking a seasonal decline in temperature (from 25 to 12°C). The latter three treatments differed in their level of thermal stochasticity: crickets experienced either no diel cycle, a predictable diel cycle, or an unpredictable diel cycle. Following these treatments, we measured several traits considered relevant to survival or reproduction, including growth rate, jumping velocity, feeding rate, metabolic rate, and cold tolerance. Contrary to our predictions, the acclimatory responses of crickets were unrelated to the magnitude or type of thermal variation. Furthermore, acclimation of performance was not ubiquitous among traits. We recommend additional studies of acclimation in fluctuating environments to assess the generality of these findings.     

UV-absorbing bacteria in coral mucus and their response to simulated temperature elevations

Reef-building corals encompass various strategies to defend against harmful ultraviolet (UV) radiation. Coral mucus contains UV-absorbing compounds and has rich prokaryotic diversity associated with it. In this study, we isolated and characterized the UV-absorbing bacteria from the mucus of the corals Porites lutea and Acropora hyacinthus during the pre-summer and summer seasons. A total of 17 UV-absorbing bacteria were isolated and sequenced. The UV-absorbing bacteria showed UV absorption at wavelengths ranging from λ _max = 333 nm to λ _min = 208 nm. Analysis of the DNA sequences revealed that the majority of the UV-absorbing bacteria belonged to the family Firmicutes and the remaining belonged to the family Proteobacteria (class Gammaproteobacteria). Comparison of the sequences with the curated database yielded four distinct bacterial groups belonging to the genus Bacillus, Staphylococcus, Salinicoccus and Vibrio. The absorption peaks for the UV-absorbing bacteria shifted to the UV-A range (320–400 nm) when they were incubated at higher temperatures. Deciphering the complex relationship between corals and their associated bacteria will help us to understand their adaptive strategies to various stresses.     

Exposure to common anesthetic agents alters pup-retrieval response in lactating rats.

This study investigated the lactating stage of rats to determine the effect on maternal behavior of a single exposure to general anesthetic. Lactating Wistar rats were treated with anesthetic doses of pentobarbital (PENT) or ketamine (KET) on day 3 or 9 of lactation, and their behavioral responses were evaluated during a 50-min nursing period, after a 4-h mother-pup separation, on day 12. Exposure to KET on day 9 led to a significantly longer latency to pup-retrieval than that of the control. Duration of pup-retrieval in mothers treated with KET on day 3 and 9 was significantly longer than in the control. Other components of maternal behavior did not differ between the groups. The present findings suggested that general anesthetics have an impact upon pup-retrieval activities, which indirectly represent maternal motivation.     

VISTA deficiency attenuates antibody-induced arthritis and alters macrophage gene expression in response to simulated immune complexes

Background

In addition to activated T cells, the immune checkpoint inhibitor “V domain-containing Ig suppressor of T-cell activation” (VISTA) is expressed by myeloid cell types, including macrophages and neutrophils. The importance of VISTA expression by myeloid cells to antibody-induced arthritis and its potential for relevance in human disease was evaluated.

Methods

VISTA was immunolocalized in normal and arthritic human synovial tissue sections and synovial tissue lysates were subjected to western blot analysis. The collagen antibody-induced arthritis model (CAIA) was performed with DBA/1 J mice treated with antibodies against VISTA and with VISTA-deficient mice (V-KO). Total mRNA from arthritic joints, spleens, and cultured macrophages was analyzed with NanoString arrays. Cytokines secreted by splenic inflammatory macrophages were determined. In-vitro chemotaxis and signal transduction assays were performed with cultured macrophages.

Results

VISTA protein was localized to synovial membrane cells, neutrophils, and scattered cells in lymphocyte-rich foci and was detected by western blot analysis in normal synovium and synovium from rheumatoid arthritis patients. Deficiency of VISTA or treatment of mice with anti-VISTA monoclonal antibodies attenuated CAIA. Joint damage and MMP-3 expression were significantly reduced in V-KO mice. Surface expression of C5a receptor was reduced on monocytes, neutrophils, and cultured macrophages from V-KO. Upon Fc receptor engagement in vitro, gene expression by V-KO macrophages was altered profoundly compared to WT, including a significant induction of IL-1 receptor antagonist (IL1rn).

Conclusions

VISTA expression supports immune-complex inflammation in CAIA and VISTA is expressed in human synovium. VISTA supports optimal responses to C5a and modulates macrophage responses to immune complexes.

     

Pregnancy alters hemodynamic responses to hemorrhage in conscious rabbits

Pregnant animals are less able to maintain mean arterial pressure (MAP) during hemorrhage compared with nonpregnant animals, but the hemodynamic basis of this difference is unknown. The hypothesis that pregnancy attenuates responses of cardiac output, as well as total peripheral resistance (TPR) and femoral conductance, to hemorrhage was tested in conscious rabbits in both the pregnant and nonpregnant state (n = 10). During continuous slow blood loss (2% of the initial blood volume per minute), MAP was maintained initially in both groups. However, MAP then abruptly decreased to <45 mmHg in all animals after a smaller percentage of the initial blood volume was removed in pregnant compared with nonpregnant rabbits (43.6 +/- 1.7%, nonpregnant; 29.6 +/- 2.2%, pregnant; P < 0.005). The more rapid transition to hypotension exhibited by pregnant rabbits was associated with greater initial falls in cardiac output (-56 +/- 10 ml/min, nonpregnant; -216 +/- 33 ml/min, pregnant; P < 0.005) and stroke volume (0.8 +/- 0.1 ml/beat, nonpregnant; -1.3 +/- 0.1 ml/beat, pregnant; P < 0.05). In addition, the increase in TPR as a function of the decrease in cardiac output was markedly attenuated (P < 0.0001) during pregnancy. Whereas femoral conductance decreased in nonpregnant rabbits, it did not change significantly in pregnant animals. In conclusion, the lesser ability of conscious pregnant rabbits to maintain MAP during hemorrhage is due largely to a greater decrease in cardiac output but also to inadequate reflex increases in TPR, possibly in part in the femoral vascular bed.     

Iron deficiency alters dopamine uptake and response to L-DOPA injection in Sprague-Dawley rats

Iron deficiency (ID) disrupts brain dopamine (DA) and norepinephrine (NE) metabolism including functioning of monoamine transporters and receptors. We employed caudate microdialysis and no net flux (NNF) in post-weaning rats to determine if ID decreased the extraction fraction ( E _d). Five micromolar quinpirole, a dopamine D₂ receptor agonist, resulted in 80% decrease in extracellular DA and 45% higher E _d in control animals. The D₂ agonist had no effect on E _d in ID animals despite a reduction in basal DA. DAT mRNA levels were reduced by 58% with ID, while DAT protein in ventral midbrain and caudate and membrane associated DAT were also reduced by ID. Carbidopa/ l -DOPA was administered to determine if elevated extracellular DA in ID was due to increased release. The DA response to l -DOPA in ID rats was 50% smaller and delayed, whereas the NE response was threefold higher. The caudate concentration of NE was also elevated in ID. Elevated dopamine-β-hydroxylase activity in ID provides a tentative explanation for the increased NE response to l -DOPA. These experiments provide new evidence that ID results in altered synthesis and functioning of DAT and perhaps suggests some compensatory changes in NE metabolism.     

Changes in the photosynthetic apparatus of maize in response to simulated natural temperature fluctuations

The response of the photosynthetic apparatus to low temperature periods differed among three hybrids of maize (Zea mays L.) grown in a phytotron. Light-saturated photosynthetic rates, leaf chlorophyll content, and mesophyll cell photosynthetic unit density all declined with increasing duration of low temperature. No single metabolic or physiological parameter appeared to control the response of the three hybrids to low temperature stress. Among all temperature treatments, net photosynthetic rate on a leaf area basis was more closely correlated with leaf chlorophyll content than with any other measured parameter. Final shoot dry weight was most highly correlated with stomatal conductance to CO₂.     

A strong static-magnetic field alters operant responding by rats

Forty male rats of the Wistar ST strain were trained and observed for Sidman avoidance (SA) for 7 weeks or for discriminative avoidance (DA) for 14 weeks to determine the effects of exposure to a strong static-magnetic field. Before avoidance conditioning was completed, rats in the SA group were exposed to the static field at 0.6 T, 16 h/day for 4 days during the fifth week, and those in the DA group were exposed for 6 h/day for 4 days during the seventh week. In the SA conditioning, frequency of lever-pressing by exposed rats gradually decreased during 1 week of exposure and stayed low for at least 2 weeks after exposure. Frequencies of electric shocks received by the rats increased dramatically during the second day of exposure and consistently stayed higher than those of control rats. In the DA condition, exposed rats responded at lower rates than did control rats throughout the observation period. They received more shocks during the 2 weeks following exposure. The data indicate that performance of avoidance responses was inhibited by a comparatively long exposure to a strong magnetic field.     

Motility of rats exposed to an altered photoperiod in the open field test

Motility of rats exposed to an altered photoperiod has been studied in the open field test. It has been shown that physical activity of rats kept in the dark declined. The correlation parameters of locomotor activity as compared with previous data changed in animals kept in continuous light.     

Influence of nicotine on the core temperature response to a novel environment in pregnant rats

Fewell, James E., and Patricia A. Tang. Influence ofnicotine on the core temperature response to a novel environment inpregnant rats. J. Appl. Physiol.83(5): 1612-1616, 1997.Exposure of a male or nonpregnant femalerat to a novel environment, such as a simulated open field, induces atransient increase in core temperature, which is often calledstress-induced hyperthermia. Pregnancy alters this response such thatthe core temperature index increases significantly during exposure to asimulated open field on day 10 but noton days 15 and20 of gestation in rats. The presentexperiments were carried to investigate the effect of chronicadministration of nicotine (0, 1, 2, 4, or 8 mg · kg¹ · 24 h¹ for 13-15 days) onthe core temperature response to a simulated open field in chronicallyinstrumented pregnant (day 20 or21 of gestation) and nonpregnantSprague-Dawley rats. In nonpregnant rats, the core temperature indexincreased more during exposure to a simulated open field after chronicadministration of nicotine at all doses than after chronicadministration of vehicle; the core temperature response was notdependent on the dose of nicotine. In pregnant rats, significantincreases in core temperature as well as in the core temperature indexoccurred only during exposure to a simulated open field after chronicadministration of nicotine in doses of 2, 4, or 8 mg · kg¹ · 24 h¹; the core temperatureresponse was dependent on the dose of nicotine. Our data provideevidence that chronic exposure to nicotine enhances the coretemperature response to a simulated open field in nonpregnant rats andunmasks a maternal thermogenic response that is not seen to the samestimulus near term of pregnancy. The possible physiological consequences for the fetus are presently unknown and requireinvestigation.

     

Soy lecithin supplementation alters macrophage phagocytosis and lymphocyte response to concanavalin A: a study in alloxan-induced diabetic rats

Dietary soy lecithin supplementation decreases hyperlipidemia and influences lipid metabolism. Although this product is used by diabetic patients, there are no data about the effect of soy lecithin supplementation on the immune system. The addition of phosphatidylcholine, the main component of lecithin, to a culture of lymphocytes has been reported to alter their function. If phosphatidylcholine changes lymphocyte functions in vitro as previously shown, then it could also affect immune cells in vivo. In the present study, the effect of dietary soy lecithin on macrophage phagocytic capacity and on lymphocyte number in response to concanavalin A (ConA) stimulation was investigated in non-diabetic and alloxan-induced diabetic rats. Supplementation was carried out daily with 2 g kg(-1) b.w. lecithin during 7 days. After that, blood was drawn from fasting rats and peritoneal macrophages and mesenteric lymph node lymphocytes were collected to determine the phospholipid content. Plasma triacylglycerol (TAG), total and HDL cholesterol and glucose levels were also determined. Lymphocytes were stimulated by ConA. The MTT (3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide) dye reduction method and flow cytometry were employed to evaluate lymphocyte metabolism and cell number, respectively. Soy lecithin supplementation significantly increased both macrophage phagocytic capacity (+29%) in non-diabetic rats and the lymphocyte number in diabetic rats (+92%). It is unlikely that plasma lipid levels indirectly affect immune cells, since plasma cholesterol, TAG, or phospholipid content was not modified by lecithin supplementation. In conclusion, lymphocyte and macrophage function were altered by lecithin supplementation, indicating an immunomodulatory effect of phosphatidylcholine.     

Microbial community response to a simulated hydrocarbon spill in mangrove sediments

In this study, we examined the hypothesis that the microbial communities in mangrove sediments with different chemical and historical characteristics respond differently to the disturbance of a hydrocarbon spill. Two different mangrove sediments were sampled, one close to an oil refinery that had suffered a recent oil spill and another that had not been in contact with oil. Based on the sampled sediment, two sets of mesocosms were built, and oil was added to one of them. They were subjected to mimicked mangrove conditions and monitored for 75 days. Archaeal and bacterial communities were evaluated through PCRDGGE. Both communities showed the emergence of small numbers of novel bands in response to oil pollution. 16S rRNA gene clone libraries were constructed from both mesocosms before the addition of oil and at day 75 after oil addition. LIBSHUFF analysis showed that both mangrove-based mesocosms contained similar communities at the start of the experiment and that they were different from the initial one, as well as from each other, after 75 days. These results hint at a role of environmental history that is not obvious from community diversity indicators, but is apparent from the response to the applied stress.     

Neonatal capsaicin treatment alters basal pulmonary mechanics and response to methacholine in F344 rats.

Full methacholine dose-response curves were performed on anesthetized tracheostomized Fischer 344 adult rats treated neonatally with capsaicin (50 mg/kg) or with vehicle alone. Capsaicin, the hot extract of pepper, releases substance P (SP) from nonmyelinated sensory nerve endings and causes acute bronchoconstriction and airway microvascular leakiness. Chronic treatment with capsaicin leads to depletion of SP and other tachykinins from afferent C-fibers and can therefore be used as a tool to investigate the contribution of SP innervation to airway responses. The rats (9 controls and 6 treated with capsaicin) were paralyzed with succinylcholine and mechanically ventilated at a constant tidal volume and frequency. Airway resistance (RL) and dynamic compliance (Cdyn) were determined at each dose of methacholine from measurements of volume, flow, and transpulmonary pressure. Capsaicin-treated rats were found to have a significantly reduced baseline RL [0.150 +/- 0.039 (SD) vs. 0.225 +/- 0.050 cmH2O.ml-1.s, P = 0.009] and a correspondingly significantly elevated Cdyn (0.371 +/- 0.084 vs. 0.268 +/- 0.053 ml/cmH2O, P = 0.012). There was no significant difference in sensitivity to methacholine, but the maximal response to methacholine was significantly greater in the capsaicin-treated rats. In terms of RL, the maximal response for capsaicin-treated rats was 6.03 x baseline +/- 0.98 vs. 4.30 x baseline +/- 1.80 (P = 0.05) for controls, and for Cdyn changes the maximal decrease was 5.75 x baseline +/- 1.22 vs. 3.83 +/- 0.69 (P = 0.002). The observed differences in RL and Cdyn coupled with the differences in maximal responses can be attributed to the selective destruction of a subpopulation of pulmonary afferent C-fibers.(ABSTRACT TRUNCATED AT 250 WORDS)     

The exploratory behavior in an open field and in a burrowing chamber of rats with different predispositions to stress]

The peculiarities of oriental research behavior and correlation between activities of catecholaminergic and serotoninergic brain systems dependently on their stress resistance degree were investigated in Wistar rats. The experiments showed that resistant (R) to a sound stimulus rats differed from nonresistant (NR) ones by increased research activity under moderate stress in the open field test and by decreased research behavior level in the cell chamber test. The biochemical analysis of biogenic amines in different brain structures revealed increased norepinephrine levels in stress R rats, and increased dopamine and serotonin levels in NR ones. The findings suggest that inborn behavior regulation in animals with different stress resistance is determined by different correlations between serotonin-dopamine and norepinephrine brain systems activities.