Electrical skin resistance and rectal temperature changes in resting human subjects exposed to heat

1. 1.|Fourteen male volunteers were examined under passive heating.

2. 2.|Electrical skin resistance (ESR) and rectal temperature (T_re) were measured during the whole period of exposure.

3. 3.|It was found that:

• —|ESR decreases rapidly with increasing air temperature. Assuming an exponential curve yields a mean time constant of 14 min.

• —|There is a correlation between the individual ESR time constants and T_re increases (r = 0.695, P < 0.005).

• —|Additional changes of ESR were noted in 8 subjects at a constant air temperature of 42°C.

4. 4.|It is concluded that ESR may be a useful indicator of the sweating response of the human thermoregulatory system during exogenous heat load.

Thermal sensitivity of chinese hamster V79 cells related to time after plating and cell-cycle redistribution

1. 1.|Cultured Chinese hamster V79 cells were trypsinized plated and grown attached or inoculated into spinner flasks and grown in suspension from exponnential growth to plateau-phase growth and their thermal sensitivity was measured after various growth times.

2. 2.|For attached cells, cultures were trypsinized and replated either 2 h before or after heating and the results were qualitatively the same: the thermal sensitivity remained approximately the same for the first 20 h and then increased and reached a maximum at 40–70 h. During this time, cells were in an exponential growth phase, and little or no change was observed in the cell-cycle age distribution as measured by flow cytometry (FMF) or [³H]thymidine pulse ([³H]Tdr) labelling.

3. 3.|At longer times after plating, cells grew into plateau phase, and thermal sensitivity decreased and became less than for the cells in exponential growth phase at the beginning of the experiment.

4. 4.|FMF and [³H]Tdr labelling showed that cells were accumulating in G₁ phase as the population density increased and that this accumulation was maximum at about 120–140 h as cells grew into plateau phase. This would account for the decrease in heat sensitivity and the increase in radiosensivity observed in plateau-phase cells.

5. 5.|For cells cultured in suspension there was no change in thermal sensitivity while cells were in exponential growth phase, As cell entered plateau phase, thermal resistance increased and most of the cell population had accumulated in G₁ as measured by FMF.

How to evaluate the risk-benefit ratio of the low-dose hormone replacement therapy?

Since the results of the women health initiative study showing an overall negative risk-benefit ratio with 0.625 mg of conjugated estrogens plus 2.5 mg of medroxyprogesterone acetate, the use of the lowest effective dose of steroids in hormone replacement therapy (HRT) is recommended.

A low-dose regimen appears to induce less side effects such as breast tenderness or leg pain than do higher dose preparations.

The decrease in hot flashes with low-dose estrogens, range 60–70%, is less than the 80–90% reduction with standard dosing. But this mean that 60–70% of menopausal women do not need higher doses.

The same applies to bone preservation which is dose dependent: the number of non-respondant women will be higher than with standard doses. However, randomized double-blind, placebo controls trials have defined positive effects on bone of low doses of HRT with adequate calcium and Vitamin D in elderly women. The use of bone densitometry and of biochemical markers of bone turnover is mandatory in women using low or ultra-low-dose preparations.

In spite of the lack of trials conducted with low-dose HRT, this treatment seems to be safer:

• the plasma levels of estradiol are lower; as far as breast cancer risk is concerned, the decrease of this subrogate marker is considered as favourable;

• the increase in breast density is less pronounced;

• the nurses's health study found a dose relationship for stroke, with no increase in risk with low-dose of estrogens;

• the effects on subrogate markers of cardiovascular risk seem to be more favourable.

Beside the low-dose HRT, one must consider some other facts:

• the “critical window” theory: it is biologically plausible that HRT, if started early after the menopause can slow the progression of coronary atherosclerosis;

• the way of administration of HRT: some observational studies have shown no increase in the risk of venous thromboembolism risk among women treated with transdermal estrogens;

• the progestogen used: a French cohort study recently performed found no increase in breast cancer risk with the use of micronized progesterone meanwhile the increase in risk observed with other progestogens was similar to the findings of the WHI study.

In the future, it is conceivable that more comprehensive pharmacogenomic studies will lead to effective algorithms for individualizing the right dose of steroids to be used in HRT.     

The ecological effect of phenotypic plasticity — Analyzing complex interaction networks (COIN) with agent-based models

Analyzing complex dynamics of ecological systems is complicated by two important facts: First, phenotypic plasticity allows individual organisms to adapt their reaction norms in terms of morphology, anatomy, physiology and behavior to changing local environmental conditions and trophic relationships. Secondly, individual reactions and ecological dynamics are often determined by indirect interactions through reaction chains and networks involving feedback processes.

We present an agent-based modeling framework which allows to represent and analyze ecological systems that include phenotypic changes in individual performances and indirect interactions within heterogeneous and temporal changing environments. We denote this structure of interacting components as COmplex Interaction Network (COIN).

Three examples illustrate the potential of the system to analyze complex ecological processes that incorporate changing phenotypes on the individual level:

• A model on fish population dynamics of roach (Rutilus rutilus) leads to a differentiation in fish length resulting in a conspicuous distribution that influences reproduction capability and thus indirectly the fitness.

• Modeling the reproduction phase of the passerine bird Erithacus rubecula (European Robin) illustrates variation in the behavior of higher organisms in dependence of environmental factors. Changes in reproduction success and in the proportion of different activities are the results.

• The morphological reaction of plants to changes in fundamental environmental parameters is illustrated by the black alder (Alnus glutinosa) model. Specification of physiological processes and the interaction structure on the level of modules allow to represent the reaction to changes in irradiance and temperature accurately.

Applying the COIN-approach, individual plasticity emerges as a structural and functional implication in a self-organized manner. The examples illustrate the potential to integrate existing approaches to represent detailed and complex traits for higher order organisms and to combine ecological and evolutionary aspects.

Hyperthermia-induced changes in the morphology of CHO-K1 and their refractile inclusions

1. 1.|Chinese hamster ovary cells (CHO-K1) were heated at temperatures of 42°C and above.

2. 2.|Cells were cultured in microcapillaries to eliminate handling stress, and morphological changes were observed by light microscopy.

3. 3.|Increased incidence of membrane blebbing was noted between 1 and 2 h and few cells were viable after 2 h at 43°C.

4. 4.|Morphological changes, including the appearance of potocytotic blebs, were recorded by cinemicroscopy of microcapillary cultures on a heated microscope stage.

5. 5.|Lipid-rich refractile cell inclusions changed shape before blebbing occurred.

6. 6.|Cell retraction and rearrangement of organelles seen at 1 h at 43°C are the reverse of those seen in spreading post-trypsinized cells and suggest a thermal effect on the cytoskeleton.

The role of the transforming a gene of SV40 in the mutagenic activity of the virus

Summary The mutagenic activity of the tsA239 mutant of SV40 which synthetizes a defective T antigen at 40°C was investigated in Chinese hamster cells under permissive and nonpermissive temperature. At 33°C the virus increased the yield of 6-mercaptopurine-resistant colonies after 2 days expression time by a factor of 1.6–4 as compared with the control and raised the frequency of aberrant metaphases after the same time by a factor of 1.9–3.4.In the same experiments, with the same initially infected population of Chinese hamster cells, at 40°C tsA SV40 did not induce either gene mutations or chromosome aberrations at the same early stage after infection. Presumably the activity of the A gene of SV40 is necessary not only for the transforming but also for the mutagenic effect of the virus.Abbreviations SV40 Simian virus 40 - BAV3 bovine adenovirus 3 - 6MP 6-mercaptopurine     

Mechanisms of heat protection by cycloheximide or puromycin: Involvement of polyamines?

1. 1.|When Chinese hamster ovary cells are treated with cycloheximide (10 μg/ml) or puromycin (100 μg/ml) for 2 h before and during heating at 43°C for 3 h, there is protection from hyperthermic killing; i.e. the plating efficiency increases 2000-fold from 3.7 × 10⁻⁵ to (6–9) × 10⁻².

2. 2.|The total intracellular levels of spermidine and spermine are not altered by the hyperthermic or drug treatments.

3. 3.|The small 30% decrease in intracellular putrescine observed after heating is not altered by drug treatment.

4. 4.|Heat protection by treatment with cycloheximide or puromycin cannot be attributed to changes in levels of total intracellular polyamines.

The synergistic effects of SV40 and BUdR on induction of gene mutations and chromosomal aberrations in chinese hamster cells

The induction of chromosomal abberations and gene mutations was studied in Chinese hamster cells after separate and combined treatment with BUdR and SV40. Separate treatment of cells with BUdR or virus infection increased the yield of chromosomal aberrations and reversions from glutamine requirement, expressed at 40°C (a ts mutant), to prototrophy. The combined effect of the incorporation of BUdR into one DNA strand, and a subsequent infection by SV40 was additive as regards the percentage of aberrant metaphases. The integration of the analogue into both DNA strands followed by SV40 treatment resulted in a statistically significant increase in the frequency of aberration-carrying metaphases, as compared with the frequency expected if the two agents had acted additively. The same phenomenon was detected when the frequency of reversions to glutamine independence was studied. Hence, the effect of the joint treatment by BUdR incorporated into both DNA strands and SV40 was synergistic. This is known to characterize the effect of BUdR on virus-induced transformation. Therefore, obviously the agent that enhances the malignant transformation of cells by the virus similarly modifies its mutagenic activity.

The results obtained are presumed to confirm the previously advanced hypothesis that the same events following infection might control both the integration of viral DNA into the host-cell chromosome (and hence cell transformation) and virus-induced mutagenesis. The role of repair processes in the synergistic effect of BUdR and SV40 in the yield of reversions to glutamine independence is discussed.     

Seasonal acclimatization in the migratory hamster Cricetulus migratorius—the role of photoperiod

1. 1.|The migratroy hamster Cricetulus migratorius, a small nocturnal rodent, inhabits ecosystems characterized by dramatic seasonal fluctuations of ambient temperatures. The aim of this study was to assess seasonal acclimatization of its thermoregulatory system.

2. 2.|Heat production by means of oxygen consumption and body temperature in various ambient temperatures as well as non-shivering thermogenesis were measured in C. migratorius. The hamsters were acclimated to two different photoperiod regimes (16L:8D and 8L:16D) at a constant ambient temprature of 24°C. Overall thermal conductance was calculated for such hamsters.

3. 3.|The results of this study indicate that photoperiod manipulations adjust the thermoregulatory system of the migratory hamster mainly by affecting overall thermal conductance.

Effect of cycloheximide on nonpermissive temperature killing in tsH1 mutant cells

1. 1.|We investigated the mechanism of cycloheximide-induced heat protection. We proposed a hypothesis to account for the mechanism [Lee and Dewey (1986) Radiat. Res. 106, 98–110].

2. 2.|Cycloheximide protects cells from hyperthermic killing by means of protecting thermolabile proteins from denaturation.

3. 3.|For this study, we have employed temperature-sensitive mutant tsH1 which contains a thermolabile leucyl-tRNA synthetase.

4. 4.|By 15 h of incubation at the nonpermissive temperature of 39.5 or 40°C, 40 or 93% of mutant cells respectively, were killed. In contrast, wild type SC cells did not lose viability after this same incubation.

5. 5.|Although killing of tsH1 by incubation at the nonpermissive temperatures was mainly due to denaturation of a thermolabile leucyl-tRNA synthetase, cycloheximide did not protect mutant cells from killing. However, tsH1 and SC cells exhibited similar sensitivities to killing at 43°C and above. Furthermore, cycloheximide protected both cell types from hyperthermic killing.

6. 6.|There was a 200- or 700-fold increase in survival after 2.5 h at 43°C by treatment with cycloheximide in tsH1 or SC cell type, respectively. Thus, the cellular target(s) for hyperthermic killing at this temperature apparently are similar in both types of cells.

7. 7.|The data indicate that the mechanism behind cycloheximide-induced heat protection is probably not the prevention of protein denaturation.

Thermosensitivity of the preoptic region and the spinal cord in the golden hamster

1. 1.|The effects of thermal stimulation of the preoptic region (POAH) and the spinal cord on non-shivering thermogenesis (NST) and shivering were studied in euthermic golden hamsters.

2. 2.|Shivering intensity is suppressed by heating the POAH but is independent of spinal cord temperature. Therefore, NST in the interscapular brown adipose tissue does not suppress shivering.

3. 3.|NST is inhibited by heating of the POAH as well as of spinal cord. It is discussed that the control of NST by two different central thermosensitive areas is significant for thermoregulation during exercise.

Mechanisms of chromosomal aberration production I. Aberration induction by ultraviolet light

We have studied chromosomal aberration production in V-79 Chinese hamster tissue culture cells by UV light administered during the post-DNA-synthetic G₂ phase of the cell cycle. The treatment produced achromatic lesions and some chromatid deletions in the first post-irradiation mitosis, but no isochromatid deletions or chromatid exchange aberrations. In contrast, when G₂ UV-irradiated cells were examined in their second post-irradiation mitosis, there were significant yields of chromatid-type aberrations of all types, including isochromatid deletions and chromatid exchanges.

We have earlier reported²¹ that UV-irradiation during the pre-DNA-synthetic G₁ phase of the cell cycle induces only chromatid aberrations and also that most chromosomal aberration production by UV in G₁ can be photoreactivated in cells possessing the photoreactivating enzyme. We present here a model for chromosomal aberration production by UV. In the model all aberration production is enzymatically mediated, a consequence of the functioning of known molecular repair mechanisms. The important elements in the model are the following:

1. (1) The vertebrate chromosome is mononeme; i.e., contains but a single DNA double helix during the prereplication G₁ phase of the cell cycle.

2. (2) The UV-induced DNA lesion leading to the production of most aberrations is the cyclobutane dimer between adjacent pyrimidines in one polynucleotide strand.

3. (3) Single chain breaks appear at metaphase as achromatic lesions.

4. (4) Dimer removal sometimes leaves unrepaired single chain gaps, possibly as a result of incomplete excision repair.

5. (5) The single-stranded DNA opposite a single chain gap can be cleaved by a single-strand DNAase.

6. (6) Gaps are left in newly synthesized DNA polynucleotide chains opposite defective template chains (i.e., opposite dimers and chain breaks).

7. (7) Double-strand breaks present following local DNA replication may “spread” to the other chromatid by a recombinational process between template and new polynucleotide chains, one from each of the homologous double helices.

The model predicts the occurrence of isoachromatic lesions and of chromatid deletions paired (isolocus) with achromatic lesions. Though often not reported, both do, in fact, occur. In addition, the model accounts for the phenomenon of sister-chromatid exchange as a manifestation of a recombinational, or post-replication, repair mechanism. Finally, the model offers a simple interpretation of chromosomal aberration production by a variety of chemical agents.     

Thermosensitivity during embryonic development of Lymnaea stagnalis (Mollusca)

1. 1.|The percentage of survival after 1 hr at 40.0°C is lowest at the larval trochophore stage and at hatching of the young snail.

2. 2.|Heat resistance depends on the stage of development.

3. 3.|From the early cleavage stage onwards a higher percentage of embryos can withstand high temperature after a previous heat treatment than without it.

4. 4.|The pattern of thermosensitivity is discussed in relation to the organizational level of the stage of development.

5. 5.|It is concluded that the developing Lymnaea is a suitable system to study heat resistance and thermotolerance at the level of cells, organs and organism.

Autonomic thermoregulatory effects of electrical stimulation of the hypothalamus in the sheep (Ovis aries)

1. 1.|The effects of electrical stimulation of the preoptic region, on autonomic thermoregulatory responses, were studied in conscious sheep at ambient temperatures of 5, 20, and 40°C.

2. 2.|Stimulation of the dorsal preoptic region elicited co-ordinated thermoregulatory responses characterized by increased respiratory frequency (RF), vasodilation of the ears and lowered body temperature. Stimulation inhibited shivering in cold environments.

3. 3.|The thermoregulatory responses were greater at 5°C in unshorn than in shorn sheep. Increased RF, induced at 20 and 40°C, persisted several minutes after stimulation ceased.

4. 4.|Intraventricular injection of noradrenaline reduced both normal and electrically-induced panting.

5. 5.|Sheep would press panels to electrically stimulate the preoptic region and this “self-stimulation” activated heat-loss mechanisms.

The effect of thermal stress on Ostrini00a nubilalis HBN (Lepidoptera, Pyralidae)—I. The orle of the neurosecretory cells in the survival of diapausing larvae

1. 1.|The effect of short-term exposure (up to 12 h) to upper limiting temperature (45°C) on A-type medial neurosecretory cells (MNSC) of the protocerebrum of Ostrinia nubilalis larvae was studied.

2. 2.|For evaluation of the activity of MNSC, cytological parameters were used: quantity of the neurosecretory material, size of the neurosecretory granules, shape of the nuclei and size of the nucleoli.

3. 3.|After 1 h exposure to 45°C the activity of the MNSC was increased, after 3 h it was decreased, while after 6 h exposure to the same temperature some renewed increase in the activity was observed.

4. 4.|The significance of oscillatory changes in the activity of A-type MNSC in survival of the thermal stress of O. nubilalis diapausing larvae is discussed.

The effect of temperature on caecal fermentation processes in a poikilothermic mammal, Heterocephalus glaber

1. 1.|The effect of temperature on caecal function was examined in the naked mole-rat Heterocephalus glaber, a poikilothermic mammal, which consumes a high proportion of fibre in its natural diet.

2. 2.|The temperature of optimal caecal function was determined from fermentation data measure at three specifically chosen temperatures (28, 33 and 40°C).

3. 3.|There was no significant difference between gas production at 33 and 40°C, however, gas production was significantly lower at 28°C.

4. 4.|The relative proportions of the gases produced were markedly different at 33 and 40°C (P ≤ 0.01). More methane and hydrogen were produced at 33°C than at 40°C.

5. 5.|These data suggest that microbial organisms within the caecum were active and functioning more effectively at 33°C (the preferred body temperature of the naked mole-rat) than at the other two temperatures.

Heat production of mammalian cells at different cell-cycle phases

1. 1.|Heat production of Reuber H35 rat hepatoma cells and murine C1300 neuroblastoma cells at different stages of the cell cycle were measured microcalorimetrically.

2. 2.|Reuber H35 monolayer cultures of G1-phase cells and cells in S-phase were trypsinized, reincubated in suspension culture and immediately used for microcalorimetric measurements. There was a remrkable difference in the heat evolution of H35-cells in suspension derived from a monolayer culture of G1-phase cells and that of cells in S-phase of the cell cycle. Heat production of G1-cells was relatively continuous during the experiment, in contrast to S-phase cells that showed a decrease in heat production after an initial maximum.

3. 3.|Neuroblastoma cells synchronized by mitotic shake-off and cultured in suspension progressed through their cell cycle. They showed maximal heat production shortly before and durign mitosis.

How are neuronal thermosensitivity and lack of thermoreception related in the duck's hypothalamus? A tentative answer

1. 1.|In 15 conscious Pekin ducks, 40 “warm sensitive” hypothalamic neurons were identified according to their discharge rates at 40°C T_hy (F₄₀), local temperature coefficients (Δ/ΔT) and Q₁₀.

2. 2.|Q₁₀ and either F₄₀ or ΔF/ΔT were little or not related.

3. 3.|A positive correlation between F₄₀ and ΔF/ΔT was observed which was particularly close (r = 0.94 and 0.96) when the neurons were classified according to their Q₁₀ of <2 and >2.

4. 4.|The results suggest that neurons with positive temperature coefficients in the duck's hypothalamus mostly exhibit linear to exponential temperature-discharge relationships.

5. 5.|This is an contrast to observations on mammalian hypothalamic thermosensitive neurons and may relate to the absence of the thermosensory function in the duck's rostral brainstem.

Comparison of thermoregulatory responses to heat between Japanese Brazilians and Japanese

1. 1. Eight male Japanese Brazilians and 11 male Japanese volunteered for this study. Each one sat on a chair for 45 min at 40°C (r.h. 50%).

2. 2. Then, they exercised using a bicycle ergometer in a semi-reclining position for 45 min at 40% of maximal oxygen uptake.

3. 3. Thermal and comfort sensation confirmed that Japanese Brazilians felt cooler and more comfortable in 40°C environment than the Japanese.

4. 4. Oxygen uptake, sweat rate and body weight loss for both groups were not significantly different.

5. 5. Forearm blood flow and heart rate for Brazilians were significantly lower than those for Japanese.

6. 6. Skin temperature at chest region for Brazilians was found to be significantly higher than that for Japanese.

7. 7. Thus the thermoregulatory responses observed in Japanese Brazilians may be largely attributed to the climate in their native places located on the Tropic of Capricorn.

8. 8. These results may indicate that environment condition is the important factor in determining the thermoregulatory responses.

The influence of heavy water (D2O) on the thermopreferendum in Drosophila melanogaster

1. 1. Thermopreferendum of contron Drosophila melanogaster flies, fed sugared water was compared with that of flies, fed sugared water containing 50% D₂O.

2. 2. Deuterium oxide increased not only the thermoresistance of some proteins, cells and the organisms, but also organism thermophilly.