Adaptive thermoregulation in golden spiny mice: the influence of season and food availability on body temperature

We studied the effect of food supplementation during summer and winter in seminatural field conditions on thermoregulation of a desert rodent, the golden spiny mouse Acomys russatus. We hypothesized that (a) under natural food availability (control conditions), mice will use less precise thermoregulation (i.e., an increase in the variance of body temperature [T(b)]) during winter because of low ambient temperatures (T(a)'s) and low food availability and during summer because of low food and water availability; (b) food supplementation will result in more precise thermoregulation during winter, but the effect will be smaller during summer because variation in T(b) in summer is also driven by water availability during that period. We found that under natural food availability, spiny mice thermoregulated more precisely during summer than during winter. They spent more time torpid during summer than during winter even when food was supplemented (although summer nights are shorter), allowing them to conserve water. Supplementing food resulted in more precise thermoregulation in both seasons, and mice spent less time torpid. In summer, thermoregulation at high T(a)'s was less precise, resulting in higher maximum T(b)'s in summer than in winter and when food was supplemented, in accord with the expected effect of water shortage on thermoregulation. Our results suggest that as expected, precise thermoregulation is beneficial when possible and is abandoned only when the costs of homeothermy outweigh the benefits.     

Fever and behavioral thermoregulation in young and old rats

At standard laboratory ambient temperatures (T(a)) of 20-24 degrees C, peripheral injections of lipopolysaccharide (LPS) reliably produce fever in young rats. In contrast, old rats may show a blunted fever, no fever, or even hypothermia after LPS. In the present study we hypothesized that old rats might use behavioral thermoregulation to help them develop a fever. Young and old rats were implanted with temperature transmitters. At least 1 wk postoperatively they were placed in a thermally graded alleyway (T(a) 10-40 degrees C). On the third and sixth day they were taken out of the gradient, placed at an T(a) of 23 degrees C, injected intraperitoneally with LPS or saline, and left at 23 degrees C for 3 h. At the end of that time, all young rats had become febrile, whereas the old rats had not. When the rats were replaced in the thermal gradient, the young animals continued to develop a fever that was similar to fever in young rats left at 23 degrees C. The old animals chose significantly warmer positions in the thermal gradient than did the young animals and only then became febrile. Although there was a tendency for the young rats to prefer higher T(a) after LPS than after saline, these differences were not significant. However, the differences in the old rats were significant. These results suggest that the LPS had increased the thermal set point in the old rats, but they could develop febrile responses only at the warm T(a) they selected.     

不同环境温度对有机磷杀虫剂毒死蜱引起大鼠体温变化的影响

目的: 观察不同环境温度对有机磷杀虫剂毒死蜱(CHP)引起大鼠体温变化的影响.方法: 用数字体温仪测量大鼠的结肠和尾部皮肤温度,观察25℃、16℃和32℃环境温度对口饲CHP引起结肠温度和尾部皮肤温度变化的影响.结果: 给置于25℃和16℃环境中的大鼠口饲CHP (20 mg·kg-1) 后,均可引起结肠温度明显的降低,尾部皮肤温度明显升高;但32℃环境中大鼠口饲CHP后却引起了明显的升温作用,而尾部皮肤温度无明显影响.结论: CHP对大鼠体温的影响与环境温度有关.     

Effects of prior or concurrent food restriction on amylin-induced changes in body weight and body composition in high-fat-fed female rats

Amylin infusion reduces food intake and slows body weight gain in rodents. In obese male rats, amylin (but not pair feeding) caused a preferential reduction of fat mass with protein preservation despite equal body weight loss in amylin-treated (fed ad libitum) and pair-fed rats. In the present study, the effect of prior or concurrent food restriction on the ability of amylin to cause weight loss was evaluated. Retired female breeder rats were maintained on a high-fat diet (40% fat) for 9 wk. Prior to drug treatment, rats were either fed ad libitum or food restricted for 10 days to lose 5% of their starting body weight. They were then subdivided into treatment groups that received either vehicle or amylin (100 microgxkg(-1)xday(-1) via subcutaneous minipump) and placed under either a restricted or ad libitum feeding schedule (for a total of 8 treatment arms). Amylin 1) significantly reduced body weight compared with vehicle under all treatment conditions, except in always restricted animals, 2) significantly decreased percent body fat in all groups, and 3) preserved lean mass in all groups. These results indicate that amylin's anorexigenic and fat-specific weight loss properties can be extended to a variety of nutritive states in female rats.     

Effects of adrenergic blockers on corticotropin-releasing factor-induced behavioral changes in rats

The effects of adrenoreceptor blocking agents on corticotropin-releasing factor (CRF)-induced behavioral changes in rats were examined. The i.c.v. injection of 1 micrograms ovine CRF significantly increased the grooming frequency, number of occurrences of rearing and total distance moved. I.c.v. administered phentolamine at a dose of 10 nmol completely suppressed the increase in rearing and total distance moved induced by CRF without affecting the grooming frequency, whereas 100 nmol phentolamine significantly decreased the grooming frequency as well as the rearing and total distance moved. In contrast, propranolol reduced the increase in rearing induced by CRF only at a dose which induced ataxia in rats. The increases in rearing and total distance moved induced by CRF were reduced by 10 nmol of yohimbine and 100 nmol of prazosin. S.c. injection of caffeine (10 mg/kg) produced a significant increase in grooming frequency, rearing, and total movement. Administration of 10 nmol phentolamine and yohimbine did not affect these behavioral changes induced by caffeine, while 100 nmol prazosin suppressed them. Therefore, prazosin depressed the behavior of rats non-specifically. These results suggest that CRF-induced behavioral hyperactivity is mediated at least in part by alpha-noradrenergic, mainly alpha 2-noradrenergic, systems in the brain.     

Effects of nicotine on body weight, food consumption and body composition in male rats

The present study examined the effects of nicotine administration and cessation on body weight, food consumption, and body composition in rats. Administration of nicotine was associated with attenuated body weight gains and cessation was associated with accelerated body weight gains. Changes in fat composition paralleled changes in body weight, whereas changes in body water and protein did not. These results suggest that nicotine administration decreases body weight through its effects on fat stores in the body. After cessation of nicotine, body fat rapidly approached levels of control animals.     

Effects of stochastic food deprivation on energy budget,body mass and activity in Swiss mice

When small animals are faced with an unpredictable food supply,they can adapt by altering different components of their energy budget such as energy intake,metabolic rate,rate of non-shivering thermogenesis(NST)or behaviour.The present study examined the effect of stochastic food deprivation(FD)on body mass,food intake,resting metabolic rate(RMR),NST and behaviour in male Swiss mice.During a period of 4 weeks' FD,animals were fed ad libitum for a randomly assigned 4 days each week,but were deprived of food ...     

Temporal changes in body mass, body composition and metabolism of gibel carp Carassius auratus gibelio during food deprivation

To investigate the response to starvation, gibel carp Carassius auratus gibelio [12.5 ± 0.03 g (mean ± SE, n = 24)] were deprived of food at 25.8 ± 0.2°C (mean ± SE, n = 56) for 56 days. Body mass, proximate composition in whole body and muscle, and respiration were measured at 7‐day intervals. Body mass decreased with prolongation of deprivation, with a significant decline recorded after 7 days deprivation. Fish lost 22% of their fresh mass and 34% of dry mass after 56 days. Fish lost 38% of the body lipid over the first 7 days, and lost body lipid at a rate of 0–11% per week over the remaining 49 days. Body protein was lost at 1–5% per week throughout deprivation. Compared with the initial composition, body lipid concentration was lower and ash concentration higher on day 7. Water as a percentage of body mass was higher after 28 days, and protein concentration lower after 42 days, than at the start of deprivation. Muscle lipid and protein concentration was lower, and % water higher, after 7 days than at the start of deprivation, whereas muscle ash concentration was relatively constant during deprivation. After 56 days, fish lost body water by 18%, body lipid by 84%, body protein by 30%, and body energy by 45%. Oxygen consumption rate dropped from day 1 to day 3, increased from day 4 to day 14, gradually decreased from day 15 to day 35, and maintained a relatively constant level from day 36 to day 56. Results of the present experiment reveal that gibel carp utilize body lipid as a major energy source in the first 7 days of food deprivation, then turn to body protein as an energy fuel when lipid reserves are heavily depleted. Oxygen consumption is maintained at a relatively low and constant level when most lipid reserves are exhausted.     

Metabolic and behavioral responses of American kestrels to food deprivation

• 1.1. The effect of short-term (79 hr) food deprivation at 27°C on body mass, locomotor activity, body temperature (T_b), and resting oxygen consumption was determined in eleven American kestrels (Falco sparverius).
• 2.2. The change in body mass during resting followed the relation, % mass remaining = 99 e^{0.07(days fasting)}. There was no significant difference in the rate of relative mass loss between males and females.
• 3.3. Locomotor activity, measured as perch hopping, was highly variable in both control and fasted birds and showed no correlation with stage of the fast, basal metabolic rate (BMR), or rate of mass loss during food deprivation.
• 4.4. Body temperatures of fasted birds declined continuously by 0.2–0.4°C per day from 39.3 to 38.3°C.
• 5.5. Both males and females responded to food deprivation with a decrease in metabolism. By the third night of fasting, BMR had declined 23.4% from 0.845 W (bird day)⁻¹ to 0.647 W (bird day)⁻¹. The observed reduction in BMR is 2.4 times that expected from a 1°C decline in T_b (assuming Q₁₀ = 2.5) indicating active suppression of metabolism.

     

Effects of GABA-transaminase inhibitor Vigabatrin on thermoregulation in rats

Vigabatrin is a GABA derivative (gamma-vinyl GABA) which inhibits irreversibly the enzyme activity of GABA transaminase and thus increased indirectly brain GABA concentrations. We have used body temperature assay to examine the effects of Vigabatrin on thermoregulation in intact rats. In order to understand the mechanism of thermoregulatory action of Vigabatrin at cellular level, we have investigated its effect on individual warm-sensitive preoptic area/anterior hypothalamus (PO/AH) neurons in rat brain slice preparations. The results of the present study suggest that Vigabatrin produced dose-dependent hypothermia in rats and also increased temperature sensitivity of warm-sensitive PO/AH neurons.     

Molecular sensors for temperature detection during behavioral thermoregulation in turtle embryos

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Effects of subanesthetic doses of inert gases on behavioral thermoregulation in mice

Mice exposed to subanesthetic partial pressures of N2O (0.25 to 0.75 atm) or N2 (5.7 or 11.33 atm) and allowed to choose between a warm and a cool environment showed a marked preference for the cooler environment. This behavior was associated with the onset of hypothermia, with deep body temperature falling by up to about 3 degrees C, usually to a new, steady level. Both the length of time spent in the cooler environment and the degree of the hypothermia produced increased with the partial pressure of N2O or N2 used. The effects of N2O on behavioral thermoregulation and body temperature were reversible. There was a correlation between anesthetic potency and the ability of both gases to alter thermoregulation, suggesting that the effect of these agents on thermoregulation was caused by the same molecular interactions as those which underlie anesthesia. Since both gases elicited changes in behavioral thermoregulation promoting rather than opposing the onset of hypothermia, it is concluded that they may have acted to lower the level at which deep body temperature was being regulated.     

Role of food intake in estradiol-induced body weight changes in female rats

In two experiments, we examined the relationship between estradiol-induced undereating and body weight loss in ovariectomized (OVX) rats. In the first experiment, both estradiol benzoate (EB) and the nonsteroidal anti-estrogen, MER-25, produced body weight losses that could not be duplicated simply by pair-feeding. In the second experiment, we compared the effects of EB treatments in obese OVX rats and in OVX rats in which the post-OVX obesity was prevented by food restriction. When fed ad libitum, both groups of oil-treated OVX rats exhibited substantial body weight gains that were not accompanied by overeating. In lean OVX rats, EB treatments caused a transient hypophagia but did not reduce body weight. These results suggest three conclusions. (1) Changes in food intake are neither necessary nor sufficient to cause some of the body weight changes induced by ovarian hormones. (2) Estradiol can depress food intake in female rats without altering the regulated body weight. (3) More attention should be paid to metabolic factors when studying gonadal influences on body weight.     

Photoperiod and thermoregulation in vertebrates: body temperature rhythms and thermogenic acclimation

Evidence has recently begun to accumulate that photoperiodic responses of mammals and birds may affect the control of energy balance and thermoregulation. Exposure to short photoperiod can lower the set point for body temperature regulation in birds and mammals, as well as the voluntarily selected body temperature in ectothermic lizards. This decrease is accompanied by a reorganization of circadian or ultradian rhythms of body temperature, particularly an increase in periods spent at rest with minimum body temperatures. Short photoperiod is also used as an environmental cue for induction of seasonal torpor or facilitation of hibernation. During winter, cold tolerance of small mammals is improved by an increase of nonshivering thermogenesis in brown fat. Thermogenic capacity of brown fat (respiratory enzymes, mitochondria, uncoupling protein) is enhanced in response to short photoperiod. This response is mediated via an increase in the activity of sympathetic innervation in brown fat. Moreover, an exposure to short photoperiod prior to low temperatures may act in preparing brown fat for facilitated thermogenesis during acclimation to cold. This shows that photoperiodic control not only affects energy balance indirectly via the control of reproduction or body mass, but may directly interact with central control of thermoregulation and may influence the process of acclimatization.