Stress-induced Hyperthermia In Mice Research Articles

Infrared thermography for non-invasive measurement of social inequality aversion in rodents and potential usefulness for future animal-friendly studies.

Infrared thermography is a method that detects thermal radiation energy and can measure the body surface temperature of animals from a distance. While rectal temperature has traditionally been used to measure animals' core temperature, thermal imaging can avoid the stress and potential rise of body temperature deriving from handling of the animals. Additionally, being non-invasive and contactless, thermal imaging allows free movement of the animals. The validity of this technique as a psychophysiological method has been proven in a series of stress-induced hyperthermia (SIH) studies of mice under social inequality conditions. Restraint in a holder elicits SIH in mice. A restrained mouse surrounded by freely moving cage mates displays increased SIH suggesting that social inequality enhances the stress. Social inequality can be examined also in unrestrained mice, in particular through unequal distribution of food. In this protocol, a food-deprived mouse is given a small piece of cheese, while its cage mate is given a large piece of cheese. This inequity causes SIH, suggesting social inequality aversion in mice. Thus, social inequality in different situations similarly increased SIH. Importantly, in future studies infrared thermography could also be used to evaluate emotional arousal states different from stress (for example to assess reactivity to rewards or in social and sexual preference tests). Moreover, the technique could be used to investigate also cognitive arousal induced by novelty. Indeed, infrared thermography could be a particularly useful tool for animal-friendly studies of cognition and emotion in rodents.

Physical contact with cage mates modifies stress-induced hyperthermia in mice

Using stress-induced hyperthermia (SIH) as an assay of stress levels, the effects of physical contact with conspecifics on restraint stress and the recovery from it were examined in mice. Restrained mice surrounded by freely moving cage mates showed enhanced SIH due to social inequality aversion. However, this stress enhancement was not observed when the subject was physically separated from cage mates by a transparent acrylic tube. Interestingly, social inequality in the dark room experimental paradigm enhanced SIH, which suggests that visual information does not play a crucial role in stress enhancement. Following release from restraint stress, the body temperatures of the mice gradually returned to baseline levels; this decrease was more rapid when the mice were placed in their home cage with cage mates. However, blocking physical contact using a transparent acrylic tube abolished the social facilitation of body temperature recovery. These results suggest that physical contact plays a crucial role in both stress emergence and recovery via social modification.

Repeated Cold Stress Enhances the Acute Restraint Stress-Induced Hyperthermia in Mice.

The rodents exposed to repeated cold stress according to a specific schedule, known as specific alternation of rhythm in temperature (SART), exhibit autonomic imbalance, and is now used as an experimental model of fibromyalgia. To explore the susceptibility of SART-stressed animals to novel acute stress, we tested whether exposure of mice to SART stress for 1 week alters the extent of acute restraint stress-induced hyperthermia. Mice were subjected to 7-d SART stress sessions; i.e., the mice were alternately exposed to 24 and 4°C at 1-h intervals during the daytime (09:00-16:00) and kept at 4°C overnight (16:00-09:00). SART-stressed and unstressed mice were exposed to acute restraint stress for 20-60 min, during which rectal temperature was monitored. Serum corticosterone levels were measured before and after 60-min exposure to restraint stress. SART stress itself did not alter the body temperature or serum corticosterone levels in mice. Acute restraint stress increased the body temperature and serum corticosterone levels, both responses being greater in SART-stressed mice than unstressed mice. The enhanced hyperthermic responses to acute restraint stress in SART-stressed mice were significantly attenuated by SR59230A, a β3 adrenoceptor antagonist, but unaffected by diazepam, an anxiolytic, mifepristone, a glucocorticoid receptor antagonist, or indomethacin, a cyclooxygenase inhibitor. These results suggest that SART stress enhances the susceptibility of mice to acute restraint stress, characterized by increased hyperthermia and corticosterone secretion, and that the increased hyperthermic responses to acute stress might involve accelerated activation of sympathetic β3 adrenoceptors, known to regulate non-shivering thermogenesis in the brown adipose tissue.

Effects of housing temperature on stress‐induced hyperthermia in mice, and the associated change in voluntary motor activity (1105.1)

Many studies that investigate stress‐induced hyperthermia (SIH) in rodents were conducted on mice housed under ambient temperatures (Ta) of 20‐22°C, which can induce chronic stress due to cold exposure. Further, SIH in mice is associated with an increase in voluntary motor activity (VMA). Given that VMA can be affected by Ta and that VMA can be a major source of heat production, we hypothesized that the amplitude of SIH, and the relationship between SIH and VMA, is affected by Ta. Two groups of 8 male mice, housed either at 21 or 27°C, were exposed to treatments known to induce varying levels of stress. For both groups. the treatments resulted The treatments for both groups resulted in an increasing SIH (control<handling<water spill<cage switch<clean cage) that was correlated to VMA; the slopes of the relationship between SIH and VMA did not differ between groups. The absolute amplitude of SIH of mice housed at 27ºC was significantly higher (by 0.45°C) than mice housed at 21°C, but the relative amplitude (during ‐ before stress) did not differ between groups. Within the range of Ta studied, we conclude that housing temperatures have minor effects on the stress response of mice.Grant Funding Source: Supported by a CSU‐AAUP grant

Stress‐induced hyperthermia in mice is, at least in part, due to increased voluntary motor activity

Most higher vertebrates exhibit an increase in body temperature when exposed to acute stress. Because voluntary motor activity (VMA) can affect body temperature and because acute stress can affect VMA, I hypothesized that this stress‐induced hyperthermia (SIH) is an artifact of changes in VMA. Body temperature and motor activity of male C57BL/6 mice were monitored by telemetry while they were exposed to varying levels of stress (control, handling, spill, cage switch, clean cage). During daytime, the treatments resulted in an increasing SIH, which was correlated to VMA. The significant differences in SIH among the treatments disappeared when VMA was included as a covariate. Similar results were obtained at night when mice are normally active. Mice pre‐treated with varying doses (0 to 300mg/kg I.P.) of sodium salicylate prior to stress exposure (clean cage) exhibited a SIH that decreased with an increasing dose of salicylate and that was correlated to VMA. The differences in SIH between the doses disappeared when VMA was included as a covariate. Based on these results I conclude that SIH in mice is, at least in part, an artifact of changes in VMA. Funded by a CSU‐AAUP grant.

Effects of a novel metabotropic glutamate receptor 7 negative allosteric modulator, 6-(4-methoxyphenyl)-5-methyl-3-pyridin-4-ylisoxazonolo[4,5- c]pyridin-4(5 H)-one (MMPIP), on the central nervous system in rodents

We recently identified 6-(4-methoxyphenyl)-5-methyl-3-pyridin-4-ylisoxazolo[4,5- c]pyridin-4(5 H)-one (MMPIP), the first allosteric metabotropic glutamate (mGlu) 7 receptor-selective negative allosteric modulator. In this study, we examined the in vivo pharmacological effects of MMPIP on the central nervous system. MMPIP was distributed into the brain after systemic administration in both mice and rats. Pharmacokinetic study revealed that the half-life of MMPIP in circulation was about 1 h in rats. Results of various behavioral studies revealed that MMPIP impaired non-spatial and spatial cognitive performances in the object recognition test and the object location test in mice, respectively. In rats, MMPIP increased time to complete the task in the 8-arm radial maze test without increasing error. In addition to impairing cognition, MMPIP decreased social interaction with reduction of line crossing in rats, while MMPIP had no effects on locomotor activity in rats and mice, rota-rod performance in mice, prepulse inhibition in rats, maternal separation-induced ultrasonic vocalization in rat pups, stress-induced hyperthermia in mice, or the tail suspension test in mice. No analgesic effects of MMPIP were detected in either the tail immersion test or formalin test in mice. MMPIP did not alter the threshold for induction of seizures by electrical shock or pentylenetetrazole in mice. These findings suggest that blockade of mGlu 7 receptors by MMPIP may modulate both non-spatial and spatial cognitive functions without non-selective inhibitory effects on the central nervous system.

Effects of acute and chronic treatment with fluoxetine on stress-induced hyperthermia in telemetered rats and mice

Preclinical and clinical evidence suggests that anxiolytic effects are observed after chronic administration of the selective serotonin reuptake inhibitor fluoxetine. In contrast, acute treatment may increase signs of anxiety. The present study examined the effects of acute and chronic administration of fluoxetine on a physiological measure of anxiety, stress-induced hyperthermia, in rats and mice using radiotelemetry to record core temperature and locomotor activity and ethologically relevant stressors to evoke the hyperthermic response. In both species, the benzodiazepine agonist chlordiazepoxide reduced stress-induced hyperthermia at doses (5 mg/kg i.p. rat, 10 mg/kg p.o. mouse) that had no significant effect on locomotor activity. Similarly, in both species, chronic (21 days) treatment with fluoxetine attenuated the hyperthermic response without significantly affecting locomotor activity. However, acute fluoxetine elicited species-specific effects. Thus in mice, stress-induced hyperthermia and activity were unaffected by fluoxetine (20 mg/kg p.o.) consistent with a lack of anxiolytic or anxiogenic activity. In contrast, in rats, fluoxetine (10 mg/kg i.p.) caused a significant baseline hypothermia in the absence of stress, confounding further interpretation. In conclusion, stress-induced hyperthermia in mice was unaffected by acute treatment and significantly reduced by chronic treatment with fluoxetine. However, in rats chronic administration of fluoxetine significantly reduced stress-induced hyperthermia while the effects of acute treatment were confounded by a decrease in body temperature in the absence of stress. Together, these observations support the view that chronic administration of fluoxetine is anxiolytic; however, the stress-induced hyperthermia assay does not reveal anxiogenic effects of acute administration of fluoxetine in rats or mice.

Effects of St. John’s Wort Extract and Single Constituents on Stress-Induced Hyperthermia in Mice

Emotional or stress-induced hyperthermia (SIH) is the rise of body temperature following exposure to psychological stress and has been demonstrated across species. In the present experiments we used exposure to an open field (OF) as inescapable stressor. Exposure of male BL6/C57J mice to OF stress significantly increased body temperature (DeltaT = 1.8 +/- 0.13 degrees C, p < 0.05). SIH is calculated as the difference (DeltaT = T (2) - T (1)) between the basal temperature (T (1)) and the temperature after exposure to an OF for 10 min (T (2)). Using this experimental design, St. John's wort extract (SJW) as well as various single compounds of it were tested for their ability to affect DeltaT. Anxiolytic drugs (the benzodiazepine diazepam; 5 mg/kg, and the 5HT (1A) receptor agonist buspirone; 10 mg/kg) significantly reduced DeltaT, whereas antidepressants (imipramine and fluoxetine) had no effect on DeltaT. Oral administration of SJW extract significantly reduced DeltaT in doses of 250 and 500 mg/kg. Higher (750 and 1000 mg/kg) as well as a lower dose (125 mg/kg) did not affect DeltaT after stress, indicating a U-shaped dose-response curve. Hypericin (0.1 mg/kg, p. o.) administered 60 min prior to testing significantly decreased DeltaT (p < 0.05) whereas hyperforin (1 - 10 mg/kg, p. o.) had no effect in this test paradigm. The flavonoids hyperoside, isoquercitrin and quercitrin (all at 0.6 mg/kg, p. o.) and rutin (1 mg/kg, p. o.) only partially blocked OF-induced hyperthermia. If compared to all other flavonoids, the quercetin 3-O-glucuronide miquelianin (1.2 mg/kg, p. o.) was the most potent compound tested in this experimental design. From the biflavonoids in SJW, only amentoflavone decreased SIH-induced hyperthermia in a dosage of 0.1 mg/kg. In conclusion, using open field stress as a psychological stressor to induce hyperthermia in mice we were able to detect putative anxiolytic effects of SJW extract and single consituents.

Anxiolytic- and Antidepressant-Like Profile of ATC0065 and ATC0175: Nonpeptidic and Orally Active Melanin-Concentrating Hormone Receptor 1 Antagonists

Melanin-concentrating hormone (MCH) is a cyclic peptide produced in the lateral hypothalamus. It has been implicated in a number of physiological processes including feeding behavior, energy balance, and the regulation of emotional states. Here, we report in vitro and in vivo profiles of ATC0065 [N(2)-[cis-4-({2-[4-bromo-2-(trifluoromethoxy)phenyl]ethyl}amino)cyclohexyl]-N(4), N(4)-dimethylquinazoline-2,4-diamine dihydrochloride] and ATC0175 [N-(cis-4-{[4-(dimethylamino)quinazolin-2-yl]amino}cyclohexyl)-3,4-difluorobenzamide hydrochloride], newly synthesized MCH receptor 1 (MCHR1) antagonists. Both ATC0065 and ATC0175 had high affinities for human MCHR1 with IC(50) values of 15.7 +/- 1.95 and 7.23 +/- 0.59 nM, respectively. Both ATC0065 (IC(50) = 21.4 +/- 1.57 nM) and ATC0175 (IC(50) = 13.5 +/- 0.78 nM) showed potent antagonist activities at MCHR1, as assessed by MCH-increased guanosine 5'-O-(3-[(35)S]thio)phosphate ([(35)S]GTPgammaS) binding to human MCHR1. Oral administration of ATC0065 (3-30 mg/kg) or ATC0175 (1-10 mg/kg) significantly reduced immobility time in the forced swimming test in rats, indicating antidepressant-like effects. Both ATC0065 and ATC0175 significantly reversed swim stress-induced anxiety in the elevated plus-maze test in rats and stress-induced hyperthermia in mice. ATC0175 significantly increased social interaction between unfamiliar rats and reduced separation-induced vocalizations in guinea pig pups, indicating anxiolytic potential. In contrast, ATC0065 and ATC0175 did not affect spontaneous locomotor activity or rotarod performance in rats. These findings indicate that ATC0065 and ATC0175 are potent and orally active MCHR1 antagonists with anxiolytic and antidepressant activity in rodents.

Behavioral characterization of the novel GABAB receptor-positive modulator GS39783 (N,N'-dicyclopentyl-2-methylsulfanyl-5-nitro-pyrimidine-4,6-diamine): anxiolytic-like activity without side effects associated with baclofen or benzodiazepines.

The role of GABAB receptors in various behavioral processes has been largely defined using the prototypical GABAB receptor agonist baclofen. However, baclofen induces sedation, hypothermia and muscle relaxation, which may interfere with its use in behavioral paradigms. Although there is much evidence for a role of the inhibitory neurotransmitter GABA in the pathophysiology of anxiety, the role of GABAB receptors in these disorders is largely unclear. We recently identified GS39783 (N,N'-dicyclopentyl-2-methylsulfanyl-5-nitro-pyrimidine-4,6-diamine) as a selective allosteric positive modulator at GABAB receptors. The aim of the present study was to broadly characterize the effects of GS39783 in well-validated rodent models for motor activity, cognition, and anxiety. The following tests were included: locomotor activity in rats and mice, rotarod and traction tests (including determinations of core temperature) in mice, passive avoidance in mice and rats, elevated plus maze in rats, elevated zero maze in mice and rats, stress-induced hyperthermia in mice, and pentobarbital- and ethanol-induced sleep in mice. Unlike baclofen and/or the benzodiazepine chlordiazepoxide, GS39783 had no effect in any of the tests for locomotion, cognition, temperature, or narcosis. Most interestingly, GS39783 had anxiolytic-like effects in all the tests used. Overall, the data obtained here suggest that positive modulation of GABAB receptors may serve as a novel therapeutic strategy for the development of anxiolytics, with a superior side effect profile to both baclofen and benzodiazepines.

Characteristics of thermoregulatory and febrile responses in mice deficient in prostaglandin EP1 and EP3 receptors.

Previous studies have disagreed about whether prostaglandin EP1 or EP3 receptors are critical for producing febrile responses. We therefore injected lipopolysaccharide (LPS) at a variety doses (1 microg kg(-1)-1 mg kg(-1)) intraperitoneally (i.p.) into wild-type (WT) mice and mice lacking the EP1 or the EP3 receptors and measured changes in core temperature (Tc) by using telemetry. In WT mice, i.p. injection of LPS at 10 microg kg(-1) increased Tc about 1 degrees C, peaking 2 h after injection. At 100 microg kg(-1), LPS increased Tc, peaking 5-8 h after injection. LPS at 1 mg kg(-1) decreased Tc, reaching a nadir at 5-8 h after injection. In EP1 receptor knockout (KO) mice injected with 10 microg kg(-1) LPS, only the initial (< 40 min) increase in Tc was lacking; with 100 microg kg(-1) LPS the mice showed no febrile response. In EP3 receptor KO mice, LPS decreased Tc in a dose- and time-dependent manner. Furthermore, in EP3 receptor KO mice subcutaneous injection of turpentine did not induce fever. Both EP1 and EP3 receptor KO mice showed a normal circadian cycle of Tc and brief hyperthermia following psychological stress (cage-exchange stress and buddy-removal stress). The present study suggests that both the EP1 and the EP3 receptors play a role in fever induced by systemic inflammation but neither EP receptor is involved in the circadian rise in Tc or psychological stress-induced hyperthermia in mice.

Stress-induced hyperthermia in mice: effects of flesinoxan on heart rate and body temperature

Stress-induced hyperthermia in mice has predictive validity for anxiolytic properties of drugs. In this paradigm, 60 min after drug administration rectal temperature is measured, which causes hyperthermia of 1–1.5°C (Δ T) in about 10 min. Flesinoxan, a selective 5-HT 1A receptor agonist with anxiolytic-like properties, causes hypothermia, which complicates interpretation of stress-induced hyperthermia. Therefore, we combined flesinoxan treatment and the stress paradigm with radiotelemetric measurement of body temperature and heart rate, which is also related to anxiety. Subjects were either undisturbed or injected with flesinoxan (0–0.1–0.3–1.0 and 3.0 mg/kg), with or without the stress paradigm. Flesinoxan (1.0 and 3.0 mg/kg) caused a relatively long-lasting hypothermia, but did not lower heart rate. The rectal temperature procedure caused hyperthermia and tachycardia. Flesinoxan reduced the stress-induced hyperthermia and the tachycardia evoked by the stress procedure. Continuous radiotelemetric measurement of heart rate, apart from body temperature, revealed that flesinoxan has anxiolytic-like properties in mice.

Behavioral Effects of Flibanserin (BIMT 17)

Flibanserin is a 5-HT 1A agonist that, in contrast to other 5-HT 1A receptor agonists, is capable of activating 5-HT 1A receptors in frontal cortex. Flibanserin also behaves as an antagonist at 5-HT 2A receptors. This compound has been described to be a putative fast-acting antidepressant owing to these properties. In the present study, the effect of flibanserin was investigated in several behavioral paradigms different from animal models of depression. Intraperitoneal flibanserin, at doses of 4–8 mg/kg, antagonized d-amphetamine– and (+)SKF-10047– induced hypermotility in mice and rats. At doses of 8–16 mg/kg, flibanserin exerted anxiolytic-like effects in the light/dark exploratory test and stress-induced hyperthermia in mice, and antagonized d-amphetamine– and apomorphine-induced stereotypy in rats. At the dose of 16 mg/kg, flibanserin reduced spontaneous motor activity in rats. At the dose of 32 mg/kg, flibanserin did not exert any clear effect on spontaneous motor activity in mice, or on the elevated plus-maze and the water maze in rats.

Effects of targeted disruption of the mouse angiotensin II type 2 receptor gene on stress-induced hyperthermia.

1. We have previously reported that brain angiotensin II type 2 receptors (AT2) contribute to immunological stress-induced hyperthermia (fever) in rats. Now, in mice, we report the effect of AT2 gene disruption on the hyperthermia induced by immunological (interleukin-1 (IL-1) injection) and non-immunological (saline injection or cage switch) stress. 2. AT2-deficient and control mice both showed typical circadian rhythmicity in body temperature and physical activity. During the latter half of the dark period, AT2-deficient mice exhibited a lower body temperature than the controls. 3. By comparison with the controls, AT2-deficient mice exhibited: (i) a significantly smaller hyperthermia after intraperitoneal (i.p.) injection of IL-1beta; (ii) significantly greater increases in body temperature and physical activity after i. p. saline; and (iii) a significantly greater hyperthermia (but a similar increase in activity) during cage-switch stress. 4. These results suggest that AT2, presumably in the brain, plays important roles in stress-induced hyperthermia in mice.

Stress-induced hyperthermia in mice: Hormonal correlates

In the stress-induced hyperthermia (SIH) paradigm in group-housed male mice, the rectal temperature of last measured mice is approximately 1.5°C higher than the first measured one when the temperature of each mouse is measured sequentially with an interval of 1 min. In the present study it is demonstrated that SIH is accompanied by increases in plasma ACTH, corticosterone, and glucose levels that return to baseline more or less parallel to the temperature. The simultaneous increases in temperature and plasma stress hormones strongly support the use of the SIH paradigm in mice as an animal model to study putative anti-stress or anxiolytic properties of drugs.

Stress-induced hyperthermia in mice: A methodological study

When the rectal temperature of group-housed mice is measured sequentially, the temperature of the last measured mouse is higher than that of the first mouse. This phenomenon is called stress-induced hyperthermia (SIH). We varied several experimental parameters to elucidate the mechanism behind this SIH. SIH was stable and found by all technicians performing the experiments. The large intertechnician difference in the mean rectal temperature could be eliminated by training in an identical fixation and handling technique. SIH was both independent of the number of handling days preceding the experiment and of the number of disturbances (0, 1, 2, or 5) implied on the mice per minute. The percentage of hyperthermic mice in 10-mice cages increased when the time interval between the individual measurements increased from 1 to 2, 5 or 10 min. In all groups the maximum increase was reached after an interval of approximately 10 min. SIH of mouse 10 returned time dependently in approximately 60 min to basal temperature. When SIH was tested on 2 or 5 successive days no tolerance developed. When animals were reused after 7 or 14 days SIH did not differ from day 1, implying that animals can be reused. When the number of mice was decreased from 10 to 5 mice per cage, the SIH of vehicle-treated mice was slightly lower in 5-mice cages compared to 10-mice cages. The blocking effects on SIH by anxiolytics was also less clear in 5-mice cages compared to 10-mice cages. Stress-induced rise in rectal temperature is a robust, reproducible, and stable phenomenon excellently suited for measuring anxiolytic activity of compounds.

The Effect of DAU 6215, A Novel 5HT-3 Antagonist, in Animal Models of Anxiety

The aim of the present study was to evaluate the effect of DAU 6215 (N-(endo-8-methyl-8-azabicyclo[3.2.1]oct-3-yl)-2, 3-dihydro-2-oxo- 1H-benzimidazol-1-carboxamide, hydrochloride), which is a 5HT-3 receptor antagonist, chemically different from the other 5HT-3 antagonists, on a wide variety of animal models sensitive to anxiolytics. Nine animal models were used. DAU 6215 was active in reducing (i) aversion to a brightly lit environment in the light/dark exploratory test in mice, (ii) unpleasant properties of an aversive drug in rats (naloxone-induced place aversion), and (iii) aggressiveness in monkeys. DAU 6215 was effective at doses ranging (a) between 10 and 1000 μg/kg given i.p. in mice, (b) between 15 and 30 μg/kg given s.c. in rats and (c) between 1 and 10 μg/kg given orally in monkeys. DAU 6215 was inactive in (iv) the elevated plus maze, (v) conflict test and (vi) emotional hypophagia in rats and in (vii) the four plates test, (viii) staircase test and (ix) stress-induced hyperthermia in mice. Diazepam was active in all tests. In contrast to diazepam, DAU 6215 did not induce place preference, suggesting the possible lack of addictive properties.