Role In Thermoregulation Research Articles

The influence of metabolic heat production on body temperature of a small lizard, Anolis carolinensis

Little is known about the impact of increased metabolism on body temperatures of small ectotherms. We found that postprandial metabolic rates of 5 g Anolis carolinensis lizards were elevated by factorial increases of 2.3 ± 1.0 (mean ± S.E.) at 26 °C and 3.8 ± 2.1 at 30 °C over their fasting rates. Cloacal body temperatures exceeded environmental temperatures by a small amount in fasted individuals (26 °C: 0.3 ± 0.02 °C, 30 °C: 0.3 ± 0.02 °C), and by a significantly larger amount in fed individuals (26 °C: 1.0 ± 0.06 °C, 30 °C: 0.8 ± 0.08 °C). We conclude that an increased metabolic rate due to specific dynamic action leads to a small but significant elevation of body temperature in this species. Comparisons with thermal increments reported for a large (750 g) varanid lizard suggest that body size has only a minor influence on body–air temperature differentials of ectotherms. This is consistent with theoretical predictions. Finally, endogenous heat production could help elevate body temperatures in the wild and therefore play a minor role in thermoregulation.

Pineal-adrenal Relationship: Modulating Effects of Glucocorticoids on Pineal Function to Ameliorate Thermal-stress in Goats

ABSTRACT : The purpose of the investigation was to establish how the pineal-adrenal axis plays an important role in thermoregulation in female goats under short-term heat stress. The study was conducted to observe the influence of glucocorticoids on pineal function in goats and its influence on stress alleviation capability. Melatonin and glucocorticoid secretions and several other endocrine and biochemical blood parameters reflecting the animals well being were determined over a one week period after goats had been exposed to 40°C and 60% relative humidity for 10 days. Six female goats were used in the study. These animals served as self controls prior to the start of the experiment. The study was conducted for a period of seventeen days in a psychrometric chamber at 40°Cand 60% relative humidity. Chemical pinealectomy was achieved using propranolol followed by exogenous hydrocortisone treatment. Blood samples were drawn twice daily after each treatment to find the effect of hydrocortisone on plasma glucose, total protein, total cholesterol, cortisol, insulin, aldosterone, melatonin and corticosterone. Chemical pinealectomy significantly (p≤0.05) affected plasma levels of the parameters studied and these could be significantly (p≤0.05) counteracted by administration of hydrocortisone. Chemical pinealectomy aggravated thermal stress, although administration of hydrocortisone could ameliorate the condition. This indicated a role of the pineal in support of thermoregulation. The study establishes the modulating effect of glucocorticoids on pineal activity to relieve thermal stress in goats. (

Metabolic effects of long-term oral ingestion of l-histidine in overweight and obese men

Animal studies have revealed that histidine (L-hist) intake and neuronal histamine action play a key role in thermoregulation, energy expenditure and feeding behaviour by different mechanisms (1‐5) . There is a need to reproduce studies of peripheral administration of the essential amino acid L-hist in human subjects to observe any role in key metabolic functions and any possible implications in the treatment of obesity and associated disorders. The aim of the present study was to examine the effect of L-hist on risk factors for the metabolic syndrome. Eighteen male participants with BMI > 25 kg/m 2 were recruited for an 8-week randomised single blinded placebo-controlled study (intervention 25 mg L-hist/kg per d (Lamberts Healthcare, UK); placebo 45 mg Casilan-90 /kg per d (Complan Foods Ltd, UK). Measurements were carried out at 0, 4 and 8 weeks and included BMR 6 , mean skin and core temperature, total cholesterol, HDL-cholesterol, LDL-cholesterol, fasting blood glucose (FBG) 7 , insulin, leptin, NEFA and percentage body fat. Analysis of data was performed using ANOVA. Results of the study revealed an interesting trend of significantly decreased weight at 4 weeks (P = 0.046) and 8 weeks (P = 0.003) when compared with baseline weight, irrespective of the type of supplementation. BMR steadily increased over the 8-week period and at a more rapid rate with L-hist supplementation. FBG decreased slightly with L-hist (3.4% from baseline) compared with the increase (5 % from baseline) observed post placebo intake. An increase in plasma insulin levels was found in the placebo group, with a 6.3 % decrease with L-hist (although this effect was not significant). Plasma NEFA concentrations increased post L-hist intake, indicating elevated lipolysis.

Cross-Latitudinal, Seasonal and Diurnal Comparisons in Thyroid Hormone Concentrations in Sled Dogs

Problem Statement: Hypothyroidism has been a common disorder in humans and dogs. Amongst a sundry of functions, the thyroid gland plays a key role in metabolism and consequently, hypothyroidism has been a common diagnosis for a decrease in performance in sled dogs. Research has indicated that a variety of environmental factors influence thyroid hormone production, of which, light exposure, climate, latitude, exercise and season demonstrate pronounced effects. Sled dogs are exposed to many of these variables and often display thyroid hormone levels that are clinically below normal ranges. Approach: This study took a cross-latitudinal naturalistic approach in determining the effects of day length, time of day, season, climate and exercise on thyroid hormone function in sled dogs. In the process, appropriate reference ranges for racing sled dogs were established that correlate with other studies involving working dogs. Results: There was a clear indication that thyroid hormones play an integral role in thermoregulation and are greatly affected by environmental cues. Unexpectedly, sled dogs in the sub Arctic were not more prone to hypothyroidism but in fact, had higher levels of most thyroid hormones than dogs residing at lower latitudes. Conclusion: An evolutionary adaptation may account for up-regulation of thyroid function in times of environmental extremes. Consequently, the normal range for most thyroid hormones in sled dogs is lower than clinical standards.

Neuropeptide FF receptors antagonist, RF9, attenuates opioid-evoked hypothermia in mice

The present study used the endpoint of hypothermia to investigate opioid and neuropeptide FF (NPFF) interactions in conscious animals. Both opioid and NPFF systems played important roles in thermoregulation, which suggested a link between opioid receptors and NPFF receptors in the production of hypothermia. Therefore, we designed a study to investigate the relationship between opioid and NPFF in control of thermoregulation in mice. The selective NPFF receptors antagonist RF9 (30nmol) injected into the third ventricle failed to induce significant effect, but it completely antagonized the hypothermia of NPFF (45 nmol) after cerebral administration in mice. In addition, RF9 (30 nmol) co-injected i.c.v. in the third ventricle reduced the hypothermia induced by morphine (5nmol,) or nociceptin/orphanin FQ (N/OFQ) (2 nmol). Neither the classical opioid receptors antagonist naloxone (10 nmol) nor NOP receptor antagonist [Nphe(1)]NC(1-13)NH(2) (7.5 nmol) reduced the hypothermia induced by the central injection of NPFF at dose of 45 nmol. Co-injected with a low dose of NPFF (5 nmol), the hypothermia of morphine (5 nmol) or N/OFQ (2 nmol) was not modified. These results suggest that NPFF receptors activation is required for opioid to produce hypothermia. In contrast, NPFF-induced hypothermia is mainly mediated by its own receptors, independent of opioid receptors in the mouse brain. This interaction, quantitated in the present study, is the first evidence that NPFF receptors mediate opioid-induced hypothermia in conscious animals.

Identification of the alpha‐2 adrenoceptor subtype causing contraction of rat lateral tail vein

Constriction of veins plays an important role in thermoregulation. Norepinephrine from sympathetic nerves can activate alpha‐2 adrenoceptors in veins causing constriction and reduced heat loss in response to cooling. We determined the alpha‐2 adrenoceptor subtype causing contraction of the rat lateral tail vein studied in vitro. Tail veins were isolated, endothelium removed, and incubated in Krebs solution at 37 degrees C. Concentration‐response curves for contraction caused by the alpha‐2 adrenoceptor agonist UK 14304 were generated in the absence and presence of the alpha‐2 adrenoceptor antagonists RX 821002 (non‐subtype selective), BRL 44408 (alpha‐2A selective), ARC 239 (alpha‐2B/C selective) and MK 912 (alpha‐2C selective). UK 14304 caused concentration‐dependent contraction of the tail vein with an EC50 of 8.3 nM. The affinities (KB) of antagonists in blocking UK14304 contraction were RX 821002 (2.3 nM), BRL 44408 (64 nM), ARC 239 (199 nM) and MK 912 (0.06 nM). The affinity of MK 912 was nearly the same as its affinity for alpha‐2C adrenoceptors reported by others, and affinities for other antagonists were consistent with alpha‐2C adrenoceptors. Thus, alpha‐2C adrenoceptors mediate UK 14304 induced contraction of the rat lateral tail vein. The development of alpha‐2C selective agents may be useful to selectively regulate venous function in diseases associated with altered thermoregulation.

Body melanization and its adaptive role in thermoregulation and tolerance against desiccating conditions in drosophilids

AbstractMelanism seems to have evolved independently through diverse mechanisms in various taxa and different ecological factors could be responsible for selective responses. Increased body melanization at higher altitudes as well as latitudes is generally considered to be adaptive for thermoregulation. Physiological traits such as body melanization and desiccation resistance have been investigated independently in diverse insect taxa at three levels: within populations, between populations and among species. A substantial number ofDrosophilastudies have reported clinal variations in both these traits along latitude. A possible link between these traits had remained unexplored in wild and laboratory populations of ectothermic insect taxa, including drosophilids, to date. Simultaneous analysis of these traits in assorted darker and lighter phenotypes in each population in the present study showed parallel changes for body melanization and desiccation resistance. The mechanistic basis of evolving desiccation resistance was explained on the basis of differential rates of water loss per hour in darker versus lighter phenotypes in six populations ofDrosophila melanogasterfrom adjacent localities differing substantially in altitude all along the Indian subcontinent. Data on cuticular impermeability suggest a possible role of melanization in desiccation tolerance. However, substantial gaps remain in extending these results to other insect taxa and further exploring the physiological and molecular changes involved in melanization for conferring desiccation resistance.

Why do vultures have bald heads? The role of postural adjustment and bare skin areas in thermoregulation

Griffon vultures (Genus Gyps) have large areas of bare skin on their body, and by changing their posture they can vary the extent to which these are covered by feathers. We used a mathematical model to estimate the amount of bare skin exposed in the postures adopted in cold and hot conditions. Measurements of heat flow through different parts of museum skins, which differed in their feather density, were then used together with the estimates of proportions of body surface covered by each feather density type, to determine rates of heat loss from the whole body. Postural change can cause the proportion of body surface composed of bare skin areas to change from 32% to 7%, and in cold conditions these changes are sufficient to account for a 52% saving in heat loss from the body. We suggest that the bare skin areas in griffon vultures may play an important role in thermoregulation.

Heat stress in a high-latitude seabird: effects of temperature and food supply on bathing and nest attendance of great skuasCatharacta skua

Birds such as great skuas Catharacta skua adapted for successful breeding at high latitudes may experience problems of heat dissipation in mild climates. Great skuas spend time bathing at freshwater sites close to breeding territories and here, we examine impacts of heat stress on bathing, foraging and nest attendance of adults during three breeding seasons with marked variation in the availability of prey (1-group sandeels Ammodytes marinus). Adults exhibited diurnal variation in bathing activity that matched heat-stress conditions. Moreover more birds bathed on days of higher average heat stress, suggesting that bathing plays a role in thermoregulation. Bathing numbers were lower in years of poor food availability, when adult attendance at territories was low, probably because lower attendance reduced the opportunity for parents to bathe without leaving chicks unattended. Chicks are normally guarded by female parents and fed by males but under conditions of low food availability territorial attendance of breeding pairs was particularly low on days of high heat stress, with chicks regularly left unattended at air temperatures exceeding 14 degrees C. Unattended chicks are at risk of being killed by neighbouring conspecifics and survival of chicks to fledging was low in the two years of low sandeel stocks. Our study indicates that for great skuas, indirect effects of climate change on prey stocks and direct effects on heat stress experienced by adults may be additive

In vivo vasodilating mechanisms: who's NOS involved?

appreciate the importance and difficulty of identifying cellular mechanisms in physiological conditions. Indeed, 7-NI was administrated by intradermal microdialysis (2 mm) allowing large local drug concentration with local effects at the site of administration and thus avoiding systemic effects. Data were normalized to the SNP-induced maximal vasodilatation performed at the end of each protocol. Changes in skin blood flow were monitored by laser‐Doppler flowmetry (LDF) that gives continuous beat-to-beat information specific to cutaneous microvascular perfusion in a non-invasive manner. LDF measurements provide a robust approach to evaluate mechanisms of microvascular dilatation and their modification by physiological perturbations. The study reported that during nNOS inhibition, the skin vasodilatation due to whole-body heating was attenuated (∼30%) in contrast to local skin heating. The authors demonstrated that, in vivo, the nNOS isoform is responsible for NO generation during centrally mediated, reflex cutaneous active vasodilatation in whole-body heating, but is not involved in increasing skin blood flow in response to axon reflex-mediated, local skin heating. This study also showed that the nNOS isoform generates NO from the very initial phase of cutaneous active vasodilatation and continues during prolonged whole-body heat stress. However, Kellogg et al. (2008) strongly suggest that NO acts to increase synergistically the vasodilating effects of other neurotransmitters rather than acting as a direct mediator of vasodilatation. Interestingly, they excluded any participation of eNOS in centrally mediated reflex cutaneous active vasodilatation since studies using l-NAME, a non-selective isoform NOS antagonist, reported approximately an identical attenuation of 30% of skin blood flow increases to that of 7-NI, a selective nNOS antagonist, highlighting the possibility that nNOS is the sole NOS

Separation of A- versus C-nociceptive inputs into spinal–brainstem circuits

This study was designed to determine the organization of nociceptive inputs with different behavioral significance into spinal–brainstem circuits in the rat. Induction of Fos protein was used to localize spinal dorsal horn and hypothalamic neurons activated by noxious heating of the hind paw dorsum at rates known to preferentially activate C- or A-heat nociceptors. This was combined with retrograde transport of cholera toxin subunit B from the dorsolateral/lateral- (DL/L-) or the ventrolateral- (VL-) periaqueductal gray (PAG) in order to map the organization of A- and C-fiber input to spinal–brainstem circuits.The majority of dorsal horn heat-activated neurons were located in laminae I and II. A significantly larger proportion of C-fiber-activated neurons projected to the VL-PAG (P<0.05) compared with its DL/L-sector. In contrast, there was no columnar separation in the projections of A-fiber-activated neurons. However, a significantly greater proportion of A-fiber-activated neurons (P<0.05) were retrogradely labeled from the DL/L-PAG, when compared with C-fiber-activated neurons. A large proportion (25–50%) of A- and C-fiber-activated neurons in the lateral spinal nucleus projected to the PAG.A-fiber-activated neurons were found throughout the rostral hypothalamus but those projecting to the PAG were focused in the lateral area of the anterior hypothalamus (LAAH), from where ∼20% projected to the VL-PAG, which was significantly more than to the DL/L PAG (P<0.05).We hypothesize that the organization of A- versus C-fiber inputs to the PAG enables the coordination of coping strategies appropriate to meet the demands imposed by these different noxious stimuli. Hypothalamic-PAG projections activated by A-fiber inputs did not reflect this level of organization and we suggest that this may relate to their role in thermoregulation as opposed to autonomic responses to particular nociceptive inputs.

Anterior chamber depth and primary angle‐closure glaucoma: an evolutionary perspective

Anterior chamber depth is an inheritable trait which is affected by age, gender and race. Over 30 years ago, Alsbirk proposed that the shallow anterior chamber, which was typical of the Greenlandic Inuit, and which brings the iris in proximity to the cornea, may have evolved as a thermoregulatory adaptation to resist corneal freezing. Here, this hypothesis is revisited. Recent population genetic data which provide evidence for migration patterns of early humans are discussed and the notions of natural selection and ocular adaptation to cold climates are considered. Problems with the hypothesis are examined, but the idea that the shallow anterior chamber has a thermoregulatory role appears sound and suggests that shallow anterior chambers may have evolved in Homo sapiens living in north-east Asia during the last Ice Age.

HYPOTHERMIA DURING ENDOTOXEMIC SHOCK IN FEMALE MICE LACKING INDUCIBLE NITRIC OXIDE SYNTHASE

The present study was undertaken to evaluate: (1) whether lipopolysaccharide LPS-induced hypothermic responses may be altered during two estrous cycle phases, proestrus and diestrus, and after ovariectomy, followed by hormonal supplementation and (2) whether nitric oxide (NO) plays a role on LPS-induced hypothermia responses in female mice. Experiments were performed on adult female wild-type (WT) C57BL and inducible NO synthase knockout (KO) mice weighing 18 to 30 g. Endotoxemia was induced by intraperitoneal LPS administration from Escherichia coli at a nonlethal dose of 10 mg/kg, and body temperature was measured by biotelemetry. Hormonal replacement was performed in ovariectomized mice through 17beta-estradiol Silastic capsules (100 mug) and s.c. injection of progesterone (0.5 mg per animal). We observed that during the diestrus phase, mice presented more intensive hypothermia than during proestrus phase, and hormonal supplementation with 17beta-estradiol and progesterone attenuated hypothermia in ovariectomized mice. During diestrus and ovariectomy, KO mice had higher hypothermic response when compared with the WT group. During proestrus, the lack of statistical difference between KO and WT mice could be consequent of lower ovarian hormones plasma levels. After hormonal replacement, hypothermia was reverted in KO groups probably because of higher ovarian hormonal levels. In summary, the results demonstrated that NO release by inducible NO synthase has an important thermoregulatory role in LPS-induced hypothermia in female mice. Besides, this involvement is directly dependent on the presence of ovarian hormones and their respective levels.

Pyruvate-sensitive AOX exists as a non-covalently associated dimer in the homeothermic spadix of the skunk cabbage, Symplocarpus renifolius

The cyanide-resistant alternative oxidase (AOX) is a homodimeric protein whose activity can be regulated by the oxidation/reduction state and by α-keto acids. To further clarify the role of AOX in the skunk cabbage, Symplocarpus renifolius, we have performed expression and functional analyses of the encoding gene. Among the various tissues in the skunk cabbage, SrAOX transcripts were found to be specifically expressed in the thermogenic spadix. Moreover, our data demonstrate that the SrAOX protein exists as a non-covalently associated dimer in the thermogenic spadix, and is more sensitive to pyruvate than to other carboxylic acids. Our results suggest that the pyruvate-mediated modification of SrAOX activity plays a significant role in thermoregulation in the skunk cabbage.

The effects of body proportions on thermoregulation: an experimental assessment of Allen's rule

Numerous studies have discussed the influence of thermoregulation on hominin body shape concluding, in accordance with Allen's rule, that the presence of relatively short limbs on both extant as well as extinct hominin populations offers an advantage for survival in cold climates by reducing the limb's surface area to volume ratio. Moreover, it has been suggested that shortening the distal limb segment compared to the proximal limb segment may play a larger role in thermoregulation due to a greater relative surface area of the shank. If longer limbs result in greater heat dissipation, we should see higher resting metabolic rates (RMR) in longer-limbed individuals when temperature conditions fall, since the resting rate will need to replace the lost heat. We collected resting oxygen consumption on volunteer human subjects to assess the correlation between RMR and lower limb length in human subjects, as well as to reexamine the prediction that shortening the distal segment would have a larger effect on heat loss and, thus, RMR than the shortening of the proximal segment. Total lower limb length exhibits a statistically significant relationship with resting metabolic rate (p < 0.001; R 2 = 0.794). While this supports the hypothesis that as limb length increases, resting metabolic rate increases, it also appears that thigh length, rather than the length of the shank, drives this relationship. The results of the present study confirm the widely-held expectation of Allen's rule, that short limbs reduce the metabolic cost of maintaining body temperature, while long limbs result in greater heat dissipation regardless of the effect of mass. The present results suggest that the shorter limbs of Neandertals, despite being energetically disadvantageous while walking, would indeed have been advantageous for thermoregulation.

Cooling augments vasoconstriction mediated by 5-HT 1 and α 2-adrenoceptors in the isolated equine digital vein: involvement of Rho kinase

The vasculature of the equine digit fulfils an important role in thermoregulation. In other species, it has been found that cooling may enhance the response of cutaneous vessels to 5-hydroxytryptamine (5-HT) and α 2-adrenoceptor agonists. Translocation of α 2-adrenoceptors to the smooth muscle cell membrane, mediated by Rho kinase, is thought to be involved in the cooling-enhanced response in mouse tail arteries. However, little is known about the effect of cooling on 5-HT receptor function. The present investigation compared the response of 5-bromo-6-(2-imidazolin-2-ylamino) quinoxaline (UK14304:1 nM to 30 μM), methoxamine (0.1 nM to 30 μM; in the presence of yohimbine 0.1 μM), 5-carboxamidotryptamine (5-CT; 0.1 nM to 10 μM) and α-methyl 5-HT (0.1 nM to 10 μM) in the isolated equine digital vein at 30 °C and 22 °C. The effect of the Rho kinase inhibitor, fasudil (1 μM), and the recovery of the response after the irreversible blockade of surface receptors with phenoxybenzamine (10 μM) or 2-ethoxy-1-ethoxycarbonyl-1,2-dihydroquinoline (EEDQ;10 μM), was established. Moderate cooling significantly increased the maximum response to α-methyl 5-HT, 5-CT and UK14304 and shifted their response curves to the left. Cooling also augmented the phenoxybenzamine- and EEDQ-resistant response to UK14304 and 5-CT, respectively. Fasudil had no effect on the contractile response at 30 °C, but completely abrogated the effect of cooling on the response to 5-CT and UK14304. The response to methoxamine was not significantly affected by cooling. These results suggest that Rho kinase plays an important role in the cooling-enhanced response mediated by 5-HT 1B/D receptors and α 2-adrenoceptors. The exact mechanism by which Rho/Rho kinase enhances the functional responses mediated by these receptors in these vessels has yet to be determined.

Effect of Aspirin Ingestion and Fitness Level on Thermal Sensation Following Acute Cold Exposure

INTRODUCTION: The relation between cold perception (i.e., an individual's ability to sense and scale thermal discomfort) following acute cold exposure (ACE) is an area that has considerable practical application to those individuals who may work in cold environments or even those that are recreationally placed in a wilderness setting. Furthermore, it is well known that fitness levels may play a role in thermoregulation and thereby thermal sensation. PURPOSE: Therefore, the goal of the present investigation was to determine if the ingestion of a placebo (PL) vs. a body weight dose of aspirin (1.16 mg.kg-1 body weight) in low fit (LF: VO2 = 36.6 ± 0.9 ml. kg. −1min-1) and high fit (HF: VO2 = 52.0 ± 1.2 ml. kg. −1min-1) males would alter the individual's perception of cold in the recovery phase (i.e., re-warming) following acute cold exposure (ACE-REC). METHODS: Ten males (25.6 ± 1.6 y) underwent pre-experimental testing to determine VO2max and body composition. Subjects underwent 2 trials in which they were required to ingest for one week prior to both trials: a capsule which was filled with cellulose (PL) or, a body weight dose of aspirin (ASA-BW). Each trial consisted of 120 min of exposure to 10oC air (ACE) and 120 min of recovery in 25oC air (ACE-REC). The Gagge Thermal Sensation Scale (1967) vs. the Modified Thermal Sensation Scale (1994) was employed to discern thermal perception at rest during ACE-REC. RESULTS: ANOVA revealed that during ACE-REC the Gagge Scale and the Modified Gagge Scale both demonstrated a main effect for time (p<0.001). However, the Gagge Scale demonstrated a trend for treatment (p=0.056), and a treatment × fitness (LF vs. HF) interaction (p = 0.047). CONCLUSION: From these data it appears that there was a differential response in thermal perception during ACE-REC with respect to treatment × fitness. In addition a trend was demonstrated with respect to treatment via the Gagge Thermal Sensation Scale.

Neck-drooping Posture in Oriental White-Backed Vultures (Gyps bengalensis): An Unsuccessful Predictor of Mortality and Its Probable Role in Thermoregulation

Populations of three Gyps vulture species in the Indian subcontinent have undergone recent rapid declines due to elevated mortality rates caused by diclofenac poisoning. Researchers have proposed that vultures adopt a previously-undescribed neck-drooping posture prior to death. Our study investigated two hypotheses: (1) neck drooping is temperature-dependent, (2) neck-drooping is indicative of poor health in Oriental White-backed Vultures (Gyps bengalensis) and is a prelude to death. Observations of neck-drooping were highly seasonal, with the majority of vultures observed neck-drooping in the hot season from April to October and no vultures observed neck-drooping during the cold months of December and January. Above a calculated threshold ambient temperature of 15.4°C (95% CI 9.9–22.5°C), there was a significant positive correlation between temperature and the proportion (expressed as an angular transformation) of vultures observed neck-drooping. Neck-drooping vultures were observed significantly more frequently with their back toward the sun with their head in their own shade than birds that were not neck-drooping, and vultures that were not neck-drooping were observed more frequently facing the sun than those neck-drooping. Together, these observations strongly suggest that neck-drooping posture has a role in thermoregulation. In contrast to the highly seasonal pattern of neck-drooping, mortality of vultures occurred in all months of the year. This finding indicates that neck-drooping has low specificity and sensitivity as an indicator of poor health and impending death in vultures.

The Role of the Selective Serotonin Reuptake Inhibitor Fluoxetine in Temperature Regulation in Ovariectomized Rat Models

Thermoregulation is an integrated network of neuroendocrine, autonomic and somatosensory responses. Thermoregulatory dysfunction occurs during fluctuations or decline of gonadal hormone levels and results in vasomotor symptoms such as hot flushes and/or night-time sweating. The neurotransmitter serotonin (5-HT), has been reported to play a role in thermoregulation via changes in extracellular 5-HT levels and/or activation of various 5-HT receptors. The purpose of this study was to evaluate the role of the selective 5-HT reuptake inhibitor (SSRI), fluoxetine (FLX), on temperature regulation using ovariectomized (OVX) rodent models of thermoregulation. Single, subcutaneous (s.c.) administration of FLX (3, 10, 30 and 60 mg/kg) dose-dependently reduced core body temperature (CBT). FLX at 3 and 10 mg/kg s.c. showed no statistically significant decrease on tail-skin temperature (TST), whereas at higher doses (30 and 60 mg/kg) a significant decrease in TST was noted in the telemetry model. To mimic chronic SSRI treatment, a 5-HT_1A antagonist (WAY-100635; 0.3 mg/kg) was administered 20 min prior to FLX (10 mg/kg). This combination showed no significant improvement on temperature dysfunction compared to FLX alone. Similarly, in a morphine-dependent model of temperature dysfunction FLX, was inactive at 10 mg/kg whereas the 30 and 60 mg/kg s.c. dose abated the naloxone-induced increase in TST by 55 and 81%, respectively. In summary, FLX affected CBT at all doses, but alleviated thermoregulatory dysfunction only at higher doses that are non-selective for the 5-HT system.

Equine sweating and anhidrosis Part 1 – equine sweating

Sweating has a variety of functions in mammals including pheromone action, excretion of waste products and maintenance of the skin surface ecosystem. In a small number of mammalian species, which includes humans and the Equidae, it also has an important role in thermoregulation. This review is focused specifically on the thermoregulatory role of sweat in Equidae and the causes of sweating failure (anhidrosis). The first part describes the glandular appearance, sweat composition, and output rates; and considers the latest theories on the glandular control and secretory mechanisms. It is concluded that the glands are not directly innervated but are controlled by the interplay of neural, humoral and paracrine factors. The secretory mechanism is not as simple as previously thought and is mediated by the dynamic interaction of activating pathways, including autocrine control not only of the secretory process but probably also of secretory cell reproduction, growth, and death.