Simulation of thermoregulation in serotonin-depleted rats subjected to acceleration fields

A computer simulation of thermoregulation in mammals during and following exposure to hypergravitational fields is developed. This simulation includes the effects of a neurotransmitter, serotonin, and the initial transients of the system when the animal is first placed in a hypergravitational field. Experimental data on the response of rats to serotonin depletion helps place the site at which serotonin acts in the model.     

Behavioral thermoregulation in mammals and birds

Thermoregulation in homoiotherms is achieved by physiological and behavioural adjustments which involve the musculature, skin, sensory capacities, hypothalamus and endocrine glands. Under thermal stress animals exhibit anorexia, body extension, gasping, languor, lethargy, excessive drinking, bathing, decreased locomotor activities, group dispersion, and shade seeking. When exposed to cold, animals show body flexure, huddling, hyperphagia, extra locomotor activities, depressed respiration and nest building. Species and breed differences in the behavioural adjustments to unfavourable climates are related to habitat, morphological characteristics of body covering, degree of physiological adaptability, degree of physiological immaturity at birth or hatching, and the number of young.     

Intracellular responses of productive hybridomas subjected to high osmotic pressure

It has previously been found tht hybridoma cells undr hyuerosmotic stress produce higher amounts of antibody. This study indentified the cellular processes and mechanisms that occur during this event. In studies fo hybridomas adpated toosmolarities ranging between 300 and 450 mOsm (uusing NaCl), antibody production increased to a saturation level while cell growth decreased progressively. At 500 mOsm, lower, cell numbers and markedly decreaased productivity resulted. Sucrose and KCl were found to induce similar trends, except to different extents.Several important change in cellulaes in cellular responses were onsserved. Elevation of osmnolarity with NaCl from 300 to 350 mOsm causes an increase of zwiterionic amino acid upatake, which, occurredvia Na(+)-dependent transport systems. In particuar, systedm A was enhanced by 1.86-fold, but noenhancement was observed for Na(+)-independent transport systems, In addition, amino acids reactive with Na(+)-dependent transport systems were onserved to be abundant within osmotically stressed hybridomas in the middle and dlate exponentoial statges. Sucroses ans Kcl caused similar uptake effects, but to a laeeser degree, as long as sodium ions were present in solution.Specific consumption rates fo glucose and glutamine incresase by 19% and 20%, respectively, under high osmolarity treatment. Thewse increases were confirmed by the 5% to 10% increase in cellular metabolic acitivity. At 350 mOsm, growth rate was slower, compared with the 300-mOsm culture, which was reflected by thelower DNA conetr4ation. Stressed cultures contained enhanced leyls of tatal RNA content could in turn increase the translation rates of proteins. This was reflected in the accumulation of both dry cell weight and total cellular protein at linear rates of 0.42 muG/10(6) cells/mOsm and 0.21 mug/10(6) cells/mOmsm, respectively, with increasing osmolarty between 300 and 450 mOsm.Overall, hybridoms increased their metabolic activities and amino acids uptake via the Na(+)-dependent symports to compensate for teh osmotically elevated external environment. These effects contribute directly and indirectly tothe increased cell mass consisting of a larger pool of amono acids, RNA, cellular proteins, and seecreted antibody produt. (c) 1995 John Wiley & Sons, Inc.     

Behavioral thermoregulation in three Hawaiian reef fishes

Synopsis The preferred temperature of three Hawaiian coral-reef fishes — Acanthurus triostegus sandvicensis, Abudefduf abdominalis, and Chaetodon multicinctus — were determined in two-chambered tanks that permitted the fish to regulate behaviorally tank temperature. Median selected temperatures over 72 h were as follows: adult C. multicinctus, 24.0° C; juvenile C. multicinctus, 27.0° C; adult Ab. abdominalis, 25.9° C; juvenile Ab. abdominalis, 30.2° C; adult Ac. triostegus, 29.2° C; juvenile Ac. triostegus, 29.3° C. Juvenile Ab. abdominalis selected significantly higher median temperatures than the adults. C. multicinctus and juvenile Ab. abdominalis selected higher median temperatures during the day than at night.Based on the senior author's dissertation submitted to the Graduate School of the University of Hawaii in partial fulfillment of the requirements for the degree of Doctor of Philosophy in Oceanography.Contribution No. 555 from the Hawaii Institute of Marine Biology, University of Hawaii, Honolulu, Hawaii.     

Behavioral thermoregulation by hypoxic rats.

To address whether a shift in hypothalamic thermal setpoint might be a significant factor in induction of hypoxic hypothermia, behavioral thermoregulation was examined in 7 female Sprague-Dawley rats implanted with radiotelethermometers for deep body temperature (Tb) measurement in a thermocline during normoxia (PO2 = 125 torr) and hypoxia (PO2 = 60 torr). Normoxic rats (TNox) selected a mean ambient temperature of 19.7 +/- 1.4 (SE) degrees C and maintained Tb at 37.0 +/- 0.2 degrees C. Hypoxic rats selected a significantly higher ambient temperature (THox = 28.6 +/- 2.2 degrees C) but maintained Tb significantly lower at 35.5 +/- 0.3 degrees C. Without a thermal gradient (ambient temperature = 25 degrees C), Tb during hypoxia was 35.4 +/- 0.4 degrees C. The maintenance of a lower body temperature during hypoxia through behavioral thermoregulation despite having warmer temperatures available supports the hypothesis that the thermoregulatory setpoint of hypoxic rats is shifted to promote thermoregulation at a lower Tb, effectively reducing oxygen demand when oxygen supply is limited.     

Behavioral thermoregulation in a tropical gastropod: links to climate change scenarios

Tropical species are vulnerable to global warming because they live at, or near to, their upper thermal threshold limits. Therefore, the predicted increase in the frequency of warming events in the tropics is expected to be critical for the survival of local species. This study explored the major environmental variables which were thought to be correlated with body temperatures (BTs) of the tropical snail Littoraria scabra at the niche level. A correlation between BT and substrate temperature (ST) was detected from field observations which suggests a possible causal relationship between both substrate and BTs. In contrast, there was no correlation between BT and air temperature. Field observations suggest that 33.4 °C may be L. scabra upper limit of substrate surface temperature, although further experiments are needed to assess if the upper limit of physiological tolerance is actually different. As L. scabra individuals were free to choose their substrata, the observed distribution pattern at the niche level is related to L. scabra's behavior. Additionally, substrate surface temperatures were very heterogeneous at centimeter scale (i.e. from 22.5 to 53.1 °C) and L. scabra was shown to select specific STs (i.e. between 22.5 and 33.4 °C) rather than microhabitat type. Therefore, L. scabra did not seem to behaviorally thermoregulate through microhabitat selection nor aggregation. In contrast, behavioral experiments showed that L. scabra has the ability to actively select a thermally favorable site over short temporal scale (i.e. individual average speed of 1.26 cm min^?1) following exposure to high temperatures above 33.4 °C. Hence, this study supports the crucial need to integrate intertidal invertebrate behavioral responses to thermal constraints in climate change studies.     

Morphological and physiological characterization of Listeria monocytogenes subjected to high hydrostatic pressure

High hydrostatic pressure is a new food preservation technology known for its capacity to inactivate spoilage and pathogenic microorganisms. That inactivation is usually assessed by the number of colonies growing on solid media after treatment. Under normal conditions the method does not permit recovery of damaged cells and may underestimate the number of cells that will remain viable and grow after a few days in high-pressure-processed foodstuffs. This study investigated the damage inflicted on Listeria monocytogenes cells treated by high pressure for 10 min at 400 MPa in pH 5.6 citrate buffer. Under these conditions, no cell growth occurred after 48 h on plate count agar. Scanning electron microscopy, light scattering by flow cytometry, and cell volume measurements were compared to evaluate the morphological changes in cells after pressurization. All these methods revealed that cellular morphology was not really affected. Esterase activity, as assessed either by enzymatic activity assays or by carboxy fluorescein diacetate fluorescence monitored by flow cytometry, was dramatically lowered, but not totally obliterated, under the effects of treatment. The measurement of propidium iodide uptake followed by flow cytometry demonstrated that membrane integrity was preserved in a small part of the population, although the membrane potential measured by analytical methods or evaluated by oxonol uptake was reduced from -86 to -5 mV. These results showed that such combined methods as fluorescent dyes monitored by flow cytometry and physiological activity measurements provide valuable indications of cellular viability.     

Behavioral thermoregulation in the migratory locust: a therapy to overcome fungal infection

We examined under laboratory conditions the thermopreference of the migratory locust, Locusta migratoria migratorioides, following infection by the entomopathogenic fungus Metarhizium anisopliae var. acridum and its influence on mycosis. Infected locusts raised their body temperature more frequently than healthy conspecifics through selection of high temperatures in a heat gradient. Thermoregulation did not, however, alter the frequency of feeding events nor the amount of food eaten by infected L. migratoria. A thermoregulation regime of a minimum of 4 h/day substantially increased survival of inoculated insects (by 85%). However, the therapeutic effect decreased when thermoregulation was delayed following inoculation of the pathogen. Thermoregulation reduced locust mortality but did not completely eliminate the fungus from infected hosts; the fungus grew and killed the insects when thermoregulation was interrupted. We suggest that periodic, short bouts of thermoregulation, when performed from the onset of infection and for an extended period of time, are sufficient to provide a therapeutic effect to infected hosts. Such thermoregulatory capacity of locusts may limit the potential of fungal pathogens as biological control agents under certain ecological conditions.     

Behavioral thermoregulation in the grass shrimp Palaemonetes vulgaris (Say).

Grass shrimp (Palaemonetes vulgaris) tested in a horizontal linear gradient trough exhibited a modal final thermal preferendum of 27 degrees C, and voluntarily occupied a 24-31 degrees C range.