Further evidence that stress hyperthermia is a fever

Interleukin-1β-induced inflammation and acetaminophen during infancy: Distinct and interactive effects on social-emotional and repetitive behavior in C57BL/6J mice

Acetaminophen (APAP) exposure early in life has been associated with increased risk of neurodevelopmental disorders in epidemiological studies. In rodent models, early-life APAP has similarly been shown to produce long-term changes in brain and behavior, including altered activity levels and social behavior. Most rodent studies to date have, nevertheless, attempted to model early-life APAP without considering that most APAP exposure occurs in a context of immune activation and/or fever. To mimic the repeated infections common during infancy, we employed the cytokine interleukin-1β (IL-1β) to induce immune activation three times during early postnatal development (i.e., day 5, 8, and 11). On these days, C57BL/6J pups were administered either IL-1β (0.2 μg/kg) or saline vehicle followed, after 45 min, by either APAP (103.9 mg/kg) or vehicle. Mice were subsequently administered a battery of tests of social-emotional and repetitive behavior. A number of distinct long-term effects of IL-1β and APAP treatments were found, including sex-specific shifts in repetitive behavior and emotional hyperthermia following early-life IL-1β and increased social caution in males following early-life APAP. We also observed significant interaction between IL-1β and APAP: as adults, 'two-hit' IL-1β + APAP females displayed greater anxiety-related thigmotaxis across a number of tests, including an open field. 'Two hit' males, in turn, showed elevated levels of avoidance of an unfamiliar social partner during a social interaction test. Our results highlight that IL-1β-induced inflammation and APAP have both distinct effects and significant interactions during early life, with enduring sex-specific effects on phenotypes relevant to neurodevelopmental disorders.

Changes in Body Surface Temperature Play an Underappreciated Role in the Avian Immune Response

AbstractFever and hypothermia are well-characterized components of systemic inflammation. However, our knowledge of the mechanisms underlying such changes in body temperature is largely limited to rodent models and other mammalian species. In mammals, high dosages of an inflammatory agent (e.g., lipopolysaccharide [LPS]) typically leads to hypothermia (decrease in body temperature below normothermic levels), which is largely driven by a reduction in thermogenesis and not changes in peripheral vasomotion (i.e., changes in blood vessel tone). In birds, however, hypothermia occurs frequently, even at lower dosages, but the thermoeffector mechanisms associated with the response remain unknown. We immune challenged zebra finches (Taeniopygia guttata) with LPS, monitored changes in subcutaneous temperature and energy balance (i.e., body mass, food intake), and assessed surface temperatures of and heat loss across the eye region, bill, and legs. We hypothesized that if birds employ thermoregulatory mechanisms similar to those of similarly sized mammals, LPS-injected individuals would reduce subcutaneous body temperature and maintain constant surface temperatures compared with saline-injected individuals. Instead, LPS-injected individuals showed a slight elevation in body temperature, and this response coincided with a reduction in peripheral heat loss, particularly across the legs, as opposed to changes in energy balance. However, we note that our interpretations should be taken with caution owing to small sample sizes within each treatment. We suggest that peripheral vasomotion, allowing for heat retention, is an underappreciated component of the sickness-induced thermoregulatory response of small birds.

Homeostatic disturbance of thermoregulatory functions in rats with chronic fatigue

Chronic fatigue syndrome (CFS) is characterized by long-lasting fatigue, and a range of symptoms, and is involved in homeostasis disruption. CFS patients frequently complain of low grade fever or chill even under normal body temperature indicating that thermosensory or thermoregulatory functions might be disturbed in CFS. However, little is known about the detailed mechanisms. To elucidate whether and how thermoregulatory function was altered during the development of chronic fatigue, we investigated temporal changes in body temperature with advance of fatigue accumulation in a chronic fatigue rat model using a wireless transponder. Our findings demonstrated that the body temperature was adaptively increased in response to fatigue loading in the early phase, but unable to retain in the late phase. The tail heat dissipation was often observed and the frequency of tail heat dissipation gradually increased initially, then decreased. In the late phase of fatigue loading, the body temperature for the tail heat dissipation phase decreased to a value lower than that for the non-dissipation phase. These results suggest that adaptive changes in thermoregulatory function occurred with fatigue progression, but this system might be disrupted by long-lasting fatigue, which may underlie the mechanism of fatigue chronification.

Ambient temperature effects on stress-induced hyperthermia in Svalbard ptarmigan

Stress-induced hyperthermia (SIH) is commonly observed during handling in homeotherms. However, in birds, handling in cold environments typically elicits hypothermia. It is unclear whether this indicates that SIH is differently regulated in this taxon or if it is due to size, because body temperature changes during handling in low temperatures have only been measured in small birds <0.03 kg (that are more likely to suffer high heat loss when handled). We have therefore studied thermal responses to handling stress in the intermediate-sized (0.5-1.0 kg) Svalbard ptarmigan (Lagopus muta hyperborea) in 0°C and -20°C, in winter and spring. Handling caused elevated core body temperature and peripheral vasoconstriction that reduced back skin temperature. Core temperature increased less, and back skin temperature decreased more, in -20°C than in 0°C, probably because of higher heat-loss rate at the lower temperature. Responses were qualitatively consistent between seasons, despite higher body condition/insulation in winter and dramatic seasonal changes in photoperiod, both of which could possibly affect stress responsiveness. Our study supports the notion that SIH is a general thermoregulatory reaction to acute stressors in endotherms, but also suggests that body size and thermal environment should be taken into account when evaluating this response in birds.

Stress-induced changes in body temperature of silver-haired bats (Lasionycteris noctivagans)

Acute stressors such as capture and handling can elicit physiological responses in endothermic animals. One example of such a response is an increase in body temperature (T_b) commonly referred to as stress-induced hyperthermia (SIH). For species that employ torpor, typically an inactive state characterized by a controlled reduction in T_b and metabolic rate, a rapid increase in T_b could be advantageous, especially in the context of escape from predators. We quantified SIH in silver-haired bats (Lasionycteris noctivagans) because they readily enter torpor and often roost in exposed places where they could be vulnerable to predators. We tested the hypothesis that handling stress causes SIH in three separate contexts: a) during the nocturnal, active phase immediately following capture during flight, b) during the diurnal, inactive phase of normothermic bats, and c) during pronounced torpor immediately following exposure to cold ambient temperature. We used a standardized protocol during which T_b was measured (as rectal temperature) immediately upon handling and, again, several minutes later. We found that SIH occurred for inactive, normothermic bats held at a warm temperature. Surprisingly, however, handling stress caused a reduction in T_b for normothermic bats following the active, flight phase and, although in the opposite direction, this cooling rate was indistinguishable from the rate of SIH for normothermic bats during the rest phase. As expected, we observed a large change in T_b during rewarming from torpor following handling. This warming rate was greater than that previously reported in the literature for any heterothermic endotherm. Rapid rewarming by silver-haired bats could reflect their tendency to roost in relatively exposed locations that may be vulnerable to predators. This study provides new information on SIH in an under-studied group of animals and illustrates the need to evaluate the hypothesis that SIH and rewarming from torpor are influenced by predation risk and activity state.

Age Dependent Hypothalamic and Pituitary Responses to Novel Environment Stress or Lipopolysaccharide in Rats

Previously, we have shown that the transcription factor nuclear factor interleukin (NF-IL)6 can be used as an activation marker for inflammatory lipopolysaccharide (LPS)-induced and psychological novel environment stress (NES) in the rat brain. Here, we aimed to investigate age dependent changes of hypothalamic and pituitary responses to NES (cage switch) or LPS (100 μg/kg) in 2 and 24 months old rats. Animals were sacrificed at specific time points, blood and brains withdrawn and analyzed using immunohistochemistry, RT-PCR and bioassays. In the old rats, telemetric recording revealed that NES-induced hyperthermia was enhanced and prolonged compared to the young group. Plasma IL-6 levels remained unchanged and hypothalamic IL-6 mRNA expression was increased in the old rats. Interestingly, this response was accompanied by a significant upregulation of corticotropin-releasing hormone mRNA expression only in young rats after NES and overall higher plasma corticosterone levels in all aged animals. Immunohistochemical analysis revealed a significant upregulation of NF-IL6-positive cells in the pituitary after NES or LPS-injection. In another important brain structure implicated in immune-to-brain communication, namely, in the median eminence (ME), NF-IL6-immunoreactivity was increased in aged animals, while the young group showed just minor activation after LPS-stimulation. Interestingly, we found a higher amount of NF-IL6-CD68-positive cells in the posterior pituitary of old rats compared to the young counterparts. Moreover, aging affected the regulation of cytokine interaction in the anterior pituitary lobe. LPS-treatment significantly enhanced the secretion of the cytokines IL-6 and TNFα into supernatants of primary cell cultures of the anterior pituitary. Furthermore, in the young rats, incubation with IL-6 and IL-10 antibodies before LPS-stimulation led to a robust decrease of IL-6 production and an increase of TNFα production by the pituitary cells. In the old rats, this specific cytokine interaction could not be detected. Overall, the present results revealed strong differences in the activation patterns and pathways between old and young rats after both stressors. The prolonged hyperthermic and inflammatory response seen in aged animals seems to be linked to dysregulated pituitary cytokine interactions and brain cell activation (NF-IL6) in the hypothalamus-pituitary-adrenal axis.

Stress-induced hyperthermia and hypothermia

Stress affects core body temperature (T_c). Many kinds of stress induce transient, monophasic hyperthermia, which diminishes gradually if the stressor is terminated. Stronger stressors produce a longer-lasting effect. Repeated/chronic stress induces anticipatory hyperthermia, reduces diurnal changes in T_c, or slightly increases T_c throughout the day. Animals that are exposed to chronic stress or a cold environment exhibit an enhanced hyperthermic response to a novel stress. These changes persist for several days after cessation of stress exposure. In contrast, long-lasting inescapable stress sometimes induces hypothermia. In healthy humans, psychologic stress induces slight increases in T_c, which are within the normal range of T_c or just above it. Some individuals, however, develop extremely high T_c (up to 41°C) when they are exposed to emotional events or show persistent low-grade high T_c (37-38°C) during or after chronic stress situations. In addition to the nature of the stressor itself, such stress-induced thermal responses are modulated by sex, age, ambient temperature, cage mates, past stressful experiences and cold exposure, and coping. Stress-induced hyperthermia is driven by mechanisms distinct from infectious fever, which requires inflammatory mediators. However, both stress and infection activate the dorsomedial hypothalamus-rostral medullary raphe region-sympathetic nerve axis to increase T_c.

Fish can show emotional fever: stress-induced hyperthermia in zebrafish

Whether fishes are sentient beings remains an unresolved and controversial question. Among characteristics thought to reflect a low level of sentience in fishes is an inability to show stress-induced hyperthermia (SIH), a transient rise in body temperature shown in response to a variety of stressors. This is a real fever response, so is often referred to as ‘emotional fever’. It has been suggested that the capacity for emotional fever evolved only in amniotes (mammals, birds and reptiles), in association with the evolution of consciousness in these groups. According to this view, lack of emotional fever in fishes reflects a lack of consciousness. We report here on a study in which six zebrafish groups with access to a temperature gradient were either left as undisturbed controls or subjected to a short period of confinement. The results were striking: compared to controls, stressed zebrafish spent significantly more time at higher temperatures, achieving an estimated rise in body temperature of about 2–4°C. Thus, zebrafish clearly have the capacity to show emotional fever. While the link between emotion and consciousness is still debated, this finding removes a key argument for lack of consciousness in fishes.

Mixing induces long-term hyperthermia in growing pigs

The purpose of this experiment was to determine whether body temperature is a sensitive parameter to measure long-term effects of stress in pigs. Mixing of unacquainted pigs is a severe stressor that has detrimental effects on health, production and welfare. We measured deep body temperature after mixing growing pigs. Five pigs of 15 weeks of age, each individually housed with a companion pig, were mixed with two unacquainted congeners. Deep body temperature, heart rate and activity were recorded by radiotelemetry 9 days prior to until 8 days after mixing. These parameters were also recorded in five control pigs (individually housed with a companion pig) during the same time span. Behaviour during the light period was recorded on videotape on the day of mixing and on three subsequent days. Mixing induced a significant rise in body temperature that lasted for 8 h after mixing. Although heart rate and general activity level did not significantly differ between mixed and control pigs, mixing significantly increased the frequency of fighting and reduced the frequency of eating. In conclusion, the present experiment shows that mixing induces a long-lasting hyperthermia in pigs. Thus, deep body temperature may be used as a sensitive parameter to measure long-term effects of stress in pigs.

Cyclic ADP-Ribose and Heat Regulate Oxytocin Release via CD38 and TRPM2 in the Hypothalamus during Social or Psychological Stress in Mice

Hypothalamic oxytocin (OT) is released into the brain by cyclic ADP-ribose (cADPR) with or without depolarizing stimulation. Previously, we showed that the intracellular free calcium concentration ([Ca²⁺]_i) that seems to trigger OT release can be elevated by β-NAD⁺, cADPR, and ADP in mouse oxytocinergic neurons. As these β-NAD⁺ metabolites activate warm-sensitive TRPM2 cation channels, when the incubation temperature is increased, the [Ca²⁺]_i in hypothalamic neurons is elevated. However, it has not been determined whether OT release is facilitated by heat in vitro or hyperthermia in vivo in combination with cADPR. Furthermore, it has not been examined whether CD38 and TRPM2 exert their functions on OT release during stress or stress-induced hyperthermia in relation to the anxiolytic roles and social behaviors of OT under stress conditions. Here, we report that OT release from the isolated hypothalami of male mice in culture was enhanced by extracellular application of cADPR or increasing the incubation temperature from 35°C to 38.5°C, and simultaneous stimulation showed a greater effect. This release was inhibited by a cADPR-dependent ryanodine receptor inhibitor and a nonspecific TRPM2 inhibitor. The facilitated release by heat and cADPR was suppressed in the hypothalamus isolated from CD38 knockout mice and CD38- or TRPM2-knockdown mice. In the course of these experiments, we noted that OT release differed markedly between individual mice under stress with group housing. That is, when male mice received cage-switch stress and eliminated due to their social subclass, significantly higher levels of OT release were found in subordinates compared with ordinates. In mice exposed to anxiety stress in an open field, the cerebrospinal fluid (CSF) OT level increased transiently at 5 min after exposure, and the rectal temperature also increased from 36.6°C to 37.8°C. OT levels in the CSF of mice with lipopolysaccharide-induced fever (+0.8°C) were higher than those of control mice. The TRPM2 mRNA levels and immunoreactivities increased in the subordinate group with cage-switch stress. These results showed that cADPR/CD38 and heat/TRPM2 are co-regulators of OT secretion and suggested that CD38 and TRPM2 are potential therapeutic targets for OT release in psychiatric diseases caused by social stress.

INSURMOUNTABLE HEAT: THE EVOLUTION AND PERSISTENCE OF DEFENSIVE HYPERTHERMIA

Fever, the rise in body temperature set point in response to infection or injury, is a highly conserved trait among vertebrates, and documented in many arthropods. Fever is known to reduce illness duration and mortality. These observations present an evolutionary puzzle: why has fever continued to be an effective response to fast-evolving pathogenic microbes across diverse phyla, and probably over countless millions of years? Framing fever as part of a more general thermal manipulation strategy that we term defensive hyperthermia, we hypothesize that the solution lies in the independent contributions to pathogen fitness played by virulence and infectivity. A host organism deploying defensive hyperthermia alters the ecological environment of an invading pathogen. To the extent that the pathogen evolves to be able to function effectively at elevated temperatures, it disadvantages itself at infecting the next (thermonormative) host, becoming more likely to be thwarted by that host's immune system and outcompeted by wild ecotype conspecifics (a genetically distinct strain adapted to specific environmental conditions) that, although more vulnerable to elevated temperatures, operate more effectively at the host's normal temperature. We evaluate this hypothesis in light of existing evidence concerning pathogen thermal specialization, and discuss theoretical and translational implications of this model.

Chronic and acute effects of stress on energy balance: are there appropriate animal models?

Stress activates multiple neural and endocrine systems to allow an animal to respond to and survive in a threatening environment. The corticotropin-releasing factor system is a primary initiator of this integrated response, which includes activation of the sympathetic nervous system and the hypothalamic-pituitary-adrenal (HPA) axis. The energetic response to acute stress is determined by the nature and severity of the stressor, but a typical response to an acute stressor is inhibition of food intake, increased heat production, and increased activity with sustained changes in body weight, behavior, and HPA reactivity. The effect of chronic psychological stress is more variable. In humans, chronic stress may cause weight gain in restrained eaters who show increased HPA reactivity to acute stress. This phenotype is difficult to replicate in rodent models where chronic psychological stress is more likely to cause weight loss than weight gain. An exception may be hamsters subjected to repeated bouts of social defeat or foot shock, but the data are limited. Recent reports on the food intake and body composition of subordinate members of group-housed female monkeys indicate that these animals have a similar phenotype to human stress-induced eaters, but there are a limited number of investigators with access to the model. Few stress experiments focus on energy balance, but more information on the phenotype of both humans and animal models during and after exposure to acute or chronic stress may provide novel insight into mechanisms that normally control body weight.

Protracted effects of chronic stress on serotonin-dependent thermoregulation

Chronic stress is known to affect serotonin (5HT) neurotransmission in the brain and to alter body temperature. The body temperature is controlled in part, by the medial preoptic area (mPOA) of the hypothalamus. To investigate the effect of chronic stress on 5HT and how it affects body temperature regulation, we examined whether exposure to a chronic unpredictable stress (CUS) paradigm produces long-term alterations in thermoregulatory function of the mPOA through decreased 5HT neurotransmission. Adult male Sprague-Dawley rats underwent 21 d of CUS. Four days after the last stress exposure, basal body temperature in the home cage and body temperature in a cold room maintained at 10 °C were recorded. The CUS rats had significantly higher subcutaneous basal body temperature at 13:00 h compared to unstressed (NoStress) rats. Whereas the NoStress rats were able to significantly elevate body temperature from basal levels at 30 and 60 min of exposure to the cold room, the CUS rats showed a hypothermic response to the cold. Treatment during CUS with metyrapone, a corticosterone synthesis inhibitor, blocked stress-induced decrease in body temperature in response to the cold challenge. CUS also decreased 5HT transporter protein immunoreactivity in the mPOA and 5HT2A/C agonist injection into the mPOA after CUS exposure caused stressed rats to exhibit a sensitized hyperthermic response to cold. These results indicate that the CUS induced changes to the 5HTergic system alter mPOA function in thermoregulation. These findings help us to explain the mechanisms underlying chronic stress-induced disorders such as chronic fatigue syndrome wherein long lasting thermoregulatory deficits are observed.

Brown adipose tissue thermogenesis contributes to emotional hyperthermia in a resident rat suddenly confronted with an intruder rat

Body temperature increases when individuals experience salient, emotionally significant events. There is controversy concerning the contribution of nonshivering thermogenesis in brown adipose tissue (BAT) to emotional hyperthermia. In the present study we compared BAT, core body, and brain temperature, and tail blood flow, simultaneously measured, to determine whether BAT thermogenesis contributes to emotional hyperthermia in a resident Sprague-Dawley rat when an intruder rat, either freely-moving or confined to a small cage, is suddenly introduced into the cage of the resident rat for 30 min. Introduction of the intruder rat promptly increased BAT, body, and brain temperatures in the resident rat. For the caged intruder these temperature increases were 1.4 ± 0.2, 0.8 ± 0.1, 1.0 ± 0.1°C, respectively, with the increase in BAT temperature being significantly greater (P < 0.01) than the increases in body and brain. The initial 5-min slope of the BAT temperature record (0.18 ± 0.02°C/min) was significantly greater (P < 0.01) than the corresponding value for body (0.10 ± 0.01°C/min) and brain (0.09 ± 0.02°C/min). Tail artery pulse amplitude fell acutely when the intruder rat was introduced, possibly contributing to the increases in body and brain temperature. Prior blockade of β3 adrenoceptors (SR59230A 10 mg/kg ip) significantly reduced the amplitude of each temperature increase. Intruder-evoked increases in BAT temperature were similar in resident rats maintained at 11°C for 3 days. In the caged intruder situation there is no bodily contact between the rats, so the stimulus is psychological rather than physical. Our study thus demonstrates that BAT thermogenesis contributes to increases in body and brain temperature occurring during emotional hyperthermia.

Activation of the inflammatory transcription factor nuclear factor interleukin-6 during inflammatory and psychological stress in the brain

BACKGROUND

The transcription factor nuclear factor interleukin 6 (NF-IL6) is known to be activated by various inflammatory stimuli in the brain. Interestingly, we recently detected NF-IL6-activation within the hypothalamus-pituitary-adrenal (HPA)-axis of rats after systemic lipopolysaccharide (LPS)-injection. Thus, the aim of the present study was to investigate whether NF-IL6 is activated during either, inflammatory, or psychological stress in the rat brain.

METHODS

Rats were challenged with either the inflammatory stimulus LPS (100 μg/kg, i.p.) or exposed to a novel environment. Core body temperature (Tb) and motor activity were monitored using telemetry, animals were killed at different time points, brains and blood removed, and primary cell cultures of the anterior pituitary lobe (AL) were investigated. Analyses were performed using immunohistochemistry, RT-PCR, and cytokine-specific bioassays.

RESULTS

Stress stimulation by a novel environment increased NF-IL6-immunoreactivity (IR) in the pituitary's perivascular macrophages and hypothalamic paraventricular cells and a rise in Tb lasting approximately 2 h. LPS stimulation lead to NF-IL6-IR in several additional cell types including ACTH-IR-positive corticotrope cells in vivo and in vitro. Two other proinflammatory transcription factors, namely signal transducer and activator of transcription (STAT)3 and NFκB, were significantly activated and partially colocalized with NF-IL6-IR in cells of the AL only after LPS-stimulation, but not following psychological stress. In vitro NF-IL6-activation was associated with induction and secretion of TNFα in folliculostellate cells, which could be antagonized by the JAK-STAT-inhibitor AG490.

CONCLUSIONS

We revealed, for the first time, that NF-IL6 activation occurs not only during inflammatory LPS stimulation, but also during psychological stress, that is, a novel environment. Both stressors were associated with time-dependent activation of NF-IL6 in different cell types of the brain and the pituitary. Moreover, while NF-IL6-IR was partially linked to STAT3 and NFκB activation, TNFα production, and ACTH-IR after LPS stimulation; this was not the case after exposure to a novel environment, suggesting distinct underlying signaling pathways. Overall, NF-IL6 can be used as a broad activation marker in the brain and might be of interest for therapeutic approaches not only during inflammatory but also psychological stress.

Order of exposure to pleasant and unpleasant odors affects autonomic nervous system response

When mammals are exposed to an odor, that odor is expected to elicit a physiological response in the autonomic nervous system. An unpleasant aversive odor causes non-invasive stress, while a pleasant odor promotes healing and relaxation in mammals. We hypothesized that pleasant odors might reduce a stress response previously induced by an aversive predator odor. Rats were thus exposed to pleasant and unpleasant odors in different orders to determine whether the order of odor exposure had an effect on the physiological response in the autonomic nervous system. The first trial examined autonomic nerve activity via sympathetic and parasympathetic nerve response while the second trial examined body temperature response. Initial exposure to a pleasant odor elicited a positive response and secondary exposure to an unpleasant odor elicited a negative response, as expected. However, we found that while initial exposure to an unpleasant odor elicited a negative stress response, subsequent secondary exposure to a pleasant odor not only did not alleviate that negative response, but actually amplified it. These findings were consistent for both the autonomic nerve activity response trial and the body temperature response trial. The trial results suggest that exposure to specific odors does not necessarily result in the expected physiological response and that the specific order of exposure plays an important role. Our study should provide new insights into our understanding of the physiological response in the autonomic nervous system related to odor memory and discrimination and point to areas that require further research.

Blood cultures for evaluation of early postoperative fever after femoral neck fracture surgery

PURPOSE

To evaluate the utility of blood cultures in the assessment of early postoperative fever in hip fracture patients with no other indicators of sepsis.

METHODS

101 blood cultures were drawn on postoperative days 0 to 5 to investigate 84 febrile episodes in 31 women and 30 men (mean age, 80 years) whose body temperature measured via the tympanic route was ≥ 38 ºC. Culture results of these 61 patients were divided into culture-positive and culture-negative groups for comparison.

RESULTS

Of the 101 blood cultures, only 2 were positive: one was obtained 5 days after dynamic hip screw fixation, and the other 4 days after hemiarthroplasty. Both blood cultures grew coagulase-negative staphylococcal species, which were deemed to be skin contaminants not requiring change of patient management. 44 of these patients were treated with oral or intravenous antibiotics for a period of time.

CONCLUSION

The risk of bacteraemia in patients with postoperative fever but no other symptoms of infection is low. Routine procurement of blood cultures in such patients is ineffective and of limited utility.

Stress-induced rise in body temperature is repeatable in free-ranging Eastern chipmunks (Tamias striatus)

In response to handling or other acute stressors, most mammals, including humans, experience a temporary rise in body temperature (T(b)). Although this stress-induced rise in T(b) has been extensively studied on model organisms under controlled environments, individual variation in this interesting phenomenon has not been examined in the field. We investigated the stress-induced rise in T(b) in free-ranging eastern chipmunks (Tamias striatus) to determine first if it is repeatable. We predicted that the stress-induced rise in T(b) should be positively correlated to factors affecting heat production and heat dissipation, including ambient temperature (T(a)), body mass (M(b)), and field metabolic rate (FMR). Over two summers, we recorded both T(b) within the first minute of handling time (T(b1)) and after 5 min of handling time (T(b5)) 294 times on 140 individuals. The mean ∆T(b) (T(b5) - T(b1)) during this short interval was 0.30 ± 0.02°C, confirming that the stress-induced rise in T(b) occurs in chipmunks. Consistent differences among individuals accounted for 40% of the total variation in ∆T(b) (i.e. the stress-induced rise in T(b) is significantly repeatable). We also found that the stress-induced rise in T(b) was positively correlated to T(a), M(b), and mass-adjusted FMR. These results confirm that individuals consistently differ in their expression of the stress-induced rise in T(b) and that the extent of its expression is affected by factors related to heat production and dissipation. We highlight some research constraints and opportunities related to the integration of this laboratory paradigm into physiological and evolutionary ecology.

Associations between open-field behaviour and stress-induced hyperthermia in two breeds of sheep

In sheep (Ovis aries) and other farm animals, routine husbandry procedures can cause negative emotions, such as fear, which are generally considered to reduce animal welfare. The open-field test (OFT) is the most widely used test to measure fearfulness in animals. The induction of psychological stress is often accompanied by an elevation of core body temperature, referred to as stress-induced hyperthermia (SIH) and both OFT and SIH were used in this study to measure fearfulness in sheep: the aim being to examine associations between behaviour in the OFT and the SIH response, using data from two breeds of sheep tested repeatedly over time. Twentyfour ewes from two breeds, Lacaune and Ripollesa, were tested for 10 min with all behaviours recorded throughout. Rectal temperature was measured immediately prior to the start of the test (T1) and 10 min after its completion (T2). SIH was measured as the difference between T2 and T1. Sheep were tested over three periods of three experimental days each. Ewes of both breeds showed consistent changes in behaviour in the OFT and a clear SIH response. Bleats and visits to the water bucket showed a clear pattern between rounds. Differences between T1 and T2 were found, T2 was higher than T1 suggesting that exposure to a novel arena caused SIH. Breed differences were found whereby T2 was 0.12°C higher in Ripollesa than Lacaune. These findings have implications for selection programmes, creating the possibility of selecting less fearful animals that will cope better with handling procedures that may induce fear. Further, they also demonstrate the importance of using both behavioural and physiological variables to evaluate fear.

Cyclooxygenase-2/microsomal prostaglandin E synthase-1 complex in the preoptic-anterior hypothalamus of the mouse: involvement through fever to intravenous lipopolysaccharide

AIM

Prostaglandin E₂ (PGE₂) is now well established as a central effector of pyrogen fever. However, questions remain on the source, local vs. blood-borne, of the compound for the early phase of the typically biphasic fever (Phases 1 and 2) to i.v. pyrogens. To verify the role of centrally formed PGE₂, we examined the cyclooxygenase (COX)/prostaglandin E synthase (PGES) complex through fever to i.v. lipopolysaccharide (LPS).

METHODS

Experiments were carried out in the conscious mouse and LPS effect was ascertained on all steps of expression - gene, protein, catalytic activity - of individual enzymes. The analysis was limited to the preoptic-anterior hypothalamus (AH/POA).

RESULTS

We found upregulation of the COX2 transcript together with an upward trend for the mPGES1 transcript during Phase 1. Coincidentally, there was a progressive increase in COX2 and mPGES1 protein expression through Phases 1 and 2. Catalytic activity for COX1 and COX2 combined was instead enhanced only in Phase 2, while mPGES1 activity remained steady at an intrinsically high level. Other COX and PGES enzymes were not modified through either Phase, and COX2/mPGES1 changes subsided with fever defervescence.

CONCLUSION

The findings confirm a key function of COX2 and mPGES1 for the synthesis of pyrogenic PGE₂ and, at the same time, document their early response to LPS. We conclude that locally formed PGE₂ in AH/POA is qualified for a role in the initiation of fever.

Reduced stress fever is accompanied by increased glucocorticoids and reduced PGE2 in adult rats exposed to endotoxin as neonates

Immune challenges during neonatal period may permanently program immune responses later in life, including endotoxin fever. We tested the hypothesis that neonatal endotoxin exposure affects stress fever in adult rats. In control rats (treated with saline as neonates; nSal) body temperature peaked approximately 1.5 degrees C during open-field stress, whereas in rats exposed to endotoxin (lipopolysaccharide, LPS) as neonates (nLPS) stress fever was significantly attenuated. Following stress, plasma corticosterone levels significantly increased from 74.29+/-7.05 ng ml(-1) to 226.29+/-9.87 ng ml(-1) in nSal rats, and from 83.43+/-10.31 ng ml(-1) to 324.7+/-36.87 ng ml(-1) in nLPS rats. Animals treated with LPS as neonates and adrenalectomized one week before experimentation no longer displayed the attenuated febrile response to stress. This attenuated stress fever caused by an increased corticosterone secretion is likely to be linked to an inhibitory effect of glucocorticoids on cyclooxygenase activity/PGE(2) production in preoptic/anteroventral third ventricular region (AV3V) since stress failed to cause a significant increase in PGE(2) in nLPS rats, and this effect was reverted by adrenalectomy. Altogether, the present results indicate that endogenous glucocorticoids are key modulators of the attenuated stress fever in adult rats treated with LPS as neonates, and they act downregulating PGE(2) production in AV3V. Moreover, our findings also support the notion that neonatal immune stimulus affects programming of stress responses during adulthood, despite the fact that inflammation and stress are two distinct processes mediated largely by different neurobiological mechanisms.

Nonshivering thermogenesis without interscapular brown adipose tissue involvement during conditioned fear in the rat

As with other forms of psychological stress, conditioned fear causes an increase in body temperature. The mechanisms underlying this stress-induced hyperthermia are not well understood, but previous research suggests that nonshivering thermogenesis might contribute, as it does during cold exposure. The major source of nonshivering thermogenesis in the rat is brown adipose tissue (BAT), and the largest BAT deposit in that species is in the interscapular area just below the skin. BAT is also under sympathetic control via β-adrenoceptors. If BAT contributes to fear-induced hyperthermia, then the interscapular skin should warm up faster than other skin areas, and this response should be suppressed by the β-adrenoceptor antagonist, propranolol. We tested this noninvasively by infrared thermography. In conscious rats, 30 min of contextual fear caused hyperthermia (as indicated by a +1.5°C increase in lumbar back skin temperature) and increased the difference in temperature between interscapular and lumbar back skin (TiScap − TBack) by +1°C. Propranolol (10 mg/kg ip) completely abolished this hyperthermia; however, the TiScap-TBack increase was not reduced. In contrast, exposure to cold air (4°C) induced a +2.7°C increase in TiScap-TBack, which was reduced to +1°C after propranolol. The results show that conditioned fear-induced hyperthermia is of nonshivering origin and mediated by β-adrenoceptors, but interscapular BAT does not contribute to it and does not appear to be activated, either.

Restraint increases afebrile body temperature but attenuates fever in Pekin ducks (Anas platyrhynchos)

In mammals, procedures such as handling, restraint, or exposure to open spaces induces an increase in body temperature (Tb). The increase in temperature shares some characteristics with pyrogen-induced fever and so is often called “stress fever.” Birds also respond to acute handling with a stress fever, which may confound thermoregulatory studies that involve animal restraint. We have measured the Tb responses of Pekin ducks on days when they were restrained and compared them to days when the birds remained unrestrained. Restraint induced a 0.5°C increase in Tb that was sustained for the entire 8 h of restraint. To determine whether the restraint-induced increase in Tb is mediated by prostaglandins (PGs) we compared the Tb responses during restraint after intraperitoneal injection with saline to the responses during restraint after injection with diclofenac sodium (15 mg/kg). There was no difference in response, suggesting that restraint affects Tb by a PG-independent mechanism. We also compared the Tb response to intramuscular injection of lipopolysaccharide (LPS; 100 μg/kg), a bacterial pyrogen, when the ducks were restrained or unrestrained. Despite Tb being higher at the time of LPS injection when the ducks were restrained, the maximum temperature reached after LPS injection was higher, and the period that Tb remained elevated was longer when the ducks were unrestrained. We conclude that restraint should be considered as a potential confounder in thermoregulatory studies in birds and presumably other species too.

Gasless laparoscopy-assisted subtotal gastrectomy for early gastric cancer: a novel minimally invasive surgery

BACKGROUND

Due to the highly invasive nature of traditional surgery and the limitation of gas-filling laparoscopic surgery in gastric cancers, we developed a new method of gasless laparoscope-assisted subtotal gastrectomy (GLASG). This study investigated the technique and clinical results of this procedure and compared it with traditional radical subtotal gastrectomy (TRSG) for early gastric cancers.

METHODOLOGY

From December 2004 to January 2006, 41 patients diagnosed with early gastric cancer were included in the study. All cases underwent subtotal gastrectomy with standard radical lymph node dissection. Twenty patients underwent GLASG, whereas the other 21 patients underwent TRSG. In the GLASG group, we performed our newly developed method using three working ports created at the bilateral subcostal and umbilicus, which provided a 3-dimensional sensation by direct vision through a minilaparotomy and laparoscopic view simultaneously. B-II gastrojejunostomy reconstruction was performed by intracorporeal anastomosis using an endostapler. The TRSG group underwent the standard open method used for gastric cancer. Preoperative characteristics and postoperative recovery between the two groups were compared.

RESULTS

The operative time was comparable between the two groups, but the bleeding was significantly less severe in the GLASG group. Postoperative pain was significantly less in the GLASG group, as well as body temperature from postoperative day 2 to 7. The number of days to first flatus, first oral intake, and discharge were all significantly less in the GLASG group. No major complications were noted in either group.

CONCLUSIONS

GLASG may be a feasible and safe procedure for early gastric cancer. Gasless laparoscopic gastrectomy has the advantages of less pain, better cosmetic outcome, and earlier recovery. The newly developed gasless environment may hybridize the advantages of open method and pure laparoscopic method.

Translational aspects of pharmacological research into anxiety disorders: the stress-induced hyperthermia (SIH) paradigm

In anxiety research, the search for models with sufficient clinical predictive validity to support the translation of animal studies on anxiolytic drugs to clinical research is often challenging. This review describes the stress-induced hyperthermia (SIH) paradigm, a model that studies the activation of the autonomic nervous system in response to stress by measuring body temperature. The reproducible and robust SIH response, combined with ease of testing, make the SIH paradigm very suitable for drug screening. We will review the current knowledge on the neurobiology of the SIH response, discuss the role of GABA(A) and serotonin (5-HT) pharmacology, as well as how the SIH response relates to infectious fever. Furthermore, we will present novel data on the SIH response variance across different mice and their sensitivity to anxiolytic drugs. The SIH response is an autonomic stress response that can be successfully studied at the level of its physiology, pharmacology, neurobiology and genetics and possesses excellent animal-to-human translational properties.

A note on variations in pig blood temperature measured at exsanguination

This study investigated the temperature of pigs’ blood as it flowed from the sticking wound at exsanguination using infra-red thermometry and how it might reflect changes in core body temperature. A total of 417 pigs were monitored over a three-day period, which included a subset of 206 pigs for which additional information concerning transport conditions and ambient temperature was also known. The range of blood temperatures recorded was large (35.6-43.2°C) with a significant number of the animals found to have blood temperatures above the pigs’ normal temperature (39 ± l°C). Within the subset of pigs, average blood temperature of all the pigs in a pen at slaughter appeared to be related to pen temperatures and position on the lorry and was sensitive enough to detect changes in environmental ambient conditions.

Procedure of rectal temperature measurement affects brain, muscle, skin, and body temperatures and modulates the effects of intravenous cocaine

Rectal probe thermometry is commonly used to measure body core temperature in rodents because of its ease of use. Although previous studies suggest that rectal measurement is stressful and results in long-lasting elevations in body temperatures, we evaluated how this procedure affects brain, muscle, skin, and core temperatures measured with chronically implanted thermocouple electrodes in rats. Our data suggest that the procedure of rectal measurement results in powerful locomotor activation, rapid and strong increases in brain, muscle, and deep body temperatures, as well as a biphasic, down-up fluctuation in skin temperature, matching the response pattern observed during tail-pinch, a representative stressful procedure. This response, moreover, did not habituate after repeated day-to-day testing. Repeated rectal probe insertions also modified temperature responses induced by intravenous cocaine. Under quiet resting conditions, cocaine moderately increased brain, muscle, and deep body temperatures. However, during repeated rectal measurements, which increased temperatures, cocaine induced both hyperthermic and hypothermic responses. Direct comparisons revealed that body temperatures measured by a rectal probe are typically lower (approximately 0.6 degrees C) and more variable than body temperatures recorded by chronically implanted electrodes; the difference is smaller at low and greater at high basal temperatures. Because of this difference and temperature increases induced by the rectal probe per se, cocaine had no significant effect on rectal temperatures compared to control animals exposed to repeated rectal probes. Therefore, although rectal temperature measurements provide a decent correlation with directly measured deep body temperatures, the arousing influence of this procedure may drastically modulate the effects of other arousing stimuli and drugs.

The stress-induced hyperthermia paradigm as a physiological animal model for anxiety: A review of pharmacological and genetic studies in the mouse

This paper reviews the function, brain mechanisms and pharmacology of stress-induced hyperthermia (SIH) in a broad context. Hyperthermia itself is induced by all stressful stimuli and can be found across numerous species, including humans. As a model for anxiety, the process of insertion of a rectal probe increases temperature ranging from about 0.5-1.5 degrees C in 10-15min is called SIH. This temperature increase can be blocked by anxiolytic drugs. The methodological as well as pharmacological aspects of the group- (G-SIH) and singly housed (SIH) version of the paradigm are described in detail. Also, an overview is presented about studies using the SIH procedure in genetically modified mice together with the potential interference with immunological induction of a febrile response. The paper also presents data that highlight some of the limitations of the SIH procedure for use of drugs like nicotine, which contain particular characteristics such as short in vivo half-life, and/or disturbance of thermoregulation. The advantages and disadvantages of the SIH procedure as a physiological model of anxiety are discussed.

The dorsomedial hypothalamus: a new player in thermoregulation

Neurons in the dorsomedial hypothalamus (DMH) play key roles in physiological responses to exteroceptive (“emotional”) stress in rats, including tachycardia. Tachycardia evoked from the DMH or seen in experimental stress in rats is blocked by microinjection of the GABAA receptor agonist muscimol into the rostral raphe pallidus (rRP), an important thermoregulatory site in the brain stem, where disinhibition elicits sympathetically mediated activation of brown adipose tissue (BAT) and cutaneous vasoconstriction in the tail. Disinhibition of neurons in the DMH also elevates core temperature in conscious rats and sympathetic activity to least significant difference interscapular BAT (IBAT) and IBAT temperature in anesthetized preparations. The latter effects are blocked by microinjection of muscimol into the rRP, while microinjection of muscimol into either the rRP or DMH suppresses increases in sympathetic nerve activity to IBAT, IBAT temperature, and core body temperature elicited either by microinjection of PGE2 into the preoptic area (an experimental model for fever), or central administration of fentanyl. Neurons concentrated in the dorsal region of the DMH project directly to the rRP, a location corresponding to that of neurons transsynaptically labeled from IBAT. Thus these neurons control nonshivering thermogenesis in rats, and their activation signals its recruitment in diverse experimental paradigms. Evidence also points to a role for neurons in the DMH in thermoregulatory cutaneous vasoconstriction, shivering, and endocrine adjustments. These directions provide intriguing avenues for future exploration that may expand our understanding of the DMH as an important hypothalamic site for the integration of autonomic, endocrine, and behavioral responses to diverse challenges.

Influence of pharmacologically-induced experimental anxiety on nociception and antinociception in rats

Animal studies reveal that diverse environmental stimuli that generate anxiety-like behaviors also induce antinociception; conversely, clinical data show that pain perception is reduced under anxiolysis. This study was conducted to investigate the influence of pharmacologically induced-anxiety on nociception and antinociception. Experimental anxiety levels were measured using the rat burying behavior test. Diazepam (0, 0.5, 1.0 and 2.0 mg/kg, i.p.) or yohimbine (0, 0.5 and 1.0 mg/kg, i.p.) were used as anxiolytic or anxiogenic drugs, respectively. To evaluate the influence of different experimental anxiety levels on nociception, the pain-induced functional impairment in the rat (PIFIR model) was used. Nociception was induced by an intra-articular injection of 15% uric acid into the knee joint of the right hind limb. Diazepam or yohimbine were administered 15 min before uric acid and the ability of the rat to use the injured hind limb was recorded. To analyze the influence of different levels of anxiety on the antinociceptive effects produced by acetylsalicylic acid (0, 31, 100 and 310 mg/kg, p.o.); this analgesic was administered 3.5 h after uric acid. Fifteen min before diazepam (2.0 mg/kg) or yohimbine (1.0 mg/kg) were administered. We found that, in the burying behavior test, diazepam and yohimbine produced a dose-dependent decrease or augment in the cumulative time of burying, effects denoting reduced or increased experimental anxiety, respectively. Diazepam or yohimbine, administered alone, was unable to produce nociception. The results showed an influence of anxiety on nociception since a decreased (by diazepam) or increased (by yohimbine) experimental anxiety prevented nociception. Control experiments showed that acetylsalicylic acid did not modify experimental anxiety in the burying behavior test, but effectively reversed the nociception induced by uric acid (15%) in the PIFIR model. Such antinociceptive effect was unmodified by the anxiolytic or anxiogenic actions of diazepam or yohimbine. Data are discussed on the bases of clinical- and animal-studies revealing interactions between anxiety and nociception.

Stress-induced cardiac stimulation and fever: Common hypothalamic origins and brainstem mechanisms

Our past results provide considerable evidence that activation of neurons somewhere in the region of the dorsomedial hypothalamus (DMH) plays a key role in the generation of many of the effects typically seen in "emotional" stress in rats, including activation of the hypothalamic-pituitary-adrenal (HPA) axis, the neuroendocrine hallmark of the generalized response to stress, and sympathetically mediated tachycardia. More recently, we demonstrated that (1) the tachycardia resulting either from chemical stimulation of the DMH or from experimental stress is markedly attenuated by microinjection of the GABAA receptor agonist muscimol, a neuronal inhibitor, into the medullary raphe pallidus (RP); and (2) the specific subregion of the DMH mediating stimulation-induced tachycardia corresponds to the dorsal hypothalamic area (DHA), a site where neurons projecting to the RP are densely concentrated. Thus, the pathway from neurons in the DHA to sympathetic premotor neurons in the RP may constitute a key relay mediating the increases in heart rate seen in emotional stress--a role that had never been proposed previously for either of these regions. Instead, sympathetic premotor neurons were known to exist in the RP but had been most closely associated with sympathetic thermoregulatory mechanisms, including activation of brown fat, the principal means for nonshivering thermogenesis in rats, and cutaneous vasoconstriction in the tail, an important method of conserving body heat in this species. These sympathetic effects serve to maintain body temperature in a cold environment or to increase it in fever--and are typically accompanied by tachycardia. Interestingly, we and others have now shown that (1) disinhibition of neurons in the DMH also increases body temperature, at least in part through activation of brown fat, (2) microinjection of the neuronal inhibitor muscimol into the DMH reduces experimental fever and the associated tachycardia in rats. We hypothesize that activation of neurons in the DMH mediates both the increased body temperature and cardiac stimulation produced in rats by experimental "emotional" stress and fever, and that these effects are mediated in large part through direct projections to sympathetic premotor neurons in the RP. Thus, this pathway may constitute a common effector circuit upon which a variety of forebrain inputs converge in response to diverse environmental challenges.

Alpha-melanocyte stimulating hormone reduces putative stress-induced sickness behaviors in isolated guinea pig pups

We have proposed that passive responses observed following maternal separation in guinea pig pups represent "stress-induced sickness behaviors" mediated by proinflammatory processes. In this study, the anti-inflammatory peptide, alpha-melanocyte stimulating hormone (alpha-MSH) administered intracerebroventricularly, but not intraperitoneally, reduced the passive responses of crouching, eye-closing, and extensive piloerection relative to levels following administration of vehicle. These findings support our hypothesis and are as would be expected if pro-inflammatory processes act centrally to promote the passive behaviors of separated guinea pig pups.

Baker yeast-induced fever in young rats: Characterization and validation of an animal model for antipyretics screening

In this study we describe a low-cost and reliable method for inducing fever in young male rats (28-30 days of age, 75-90 g), which seems suitable for the screening of new antipyretics. The effects of temperature measuring procedure-induced stress on the basal rectal temperature and on Baker yeast-induced hyperthermia was assessed. Rectal temperature (T) was recorded every hour for 12 h (07:00-19:00 h) with a lubricated thermistor probe. The animals were injected intraperitoneally with baker yeast (0.25, 0.135, 0.05 g/kg) or the equivalent volume of saline at 7:00 h. The administration of 0.135 g/kg baker yeast induced a sustained increase in rectal temperature for 4 h. Classical (dipyrone and acetaminophen) and novel (MPCA and FPCA) antipyretics, at doses that had no effect per se, reverted baker yeast-induced fever. The method presented induces a clear-cut fever, which is reverted by antipyretics commonly used in human beings and selected novel antipyretics in small animals. The method also allows antipyretic evaluation with low amount of drugs, due to the use of small animals and to the small variability of the pyretic response, which ultimately causes a significant reduction in the number of animals necessary for antipyretic evaluation. Therefore, this study describes an animal model of fever that is not only advantageous from the economical and technical point of view, but that also bears ethical concerns.

Behavioral responses during the forced swim test are not affected by anti-inflammatory agents or acute illness induced by lipopolysaccharide

Pro-inflammatory cytokines and other molecules traditionally associated with immune function have been implicated in mediating behavioral and physiological consequences of stressor exposure. There is also evidence that cytokines are aberrantly expressed in depressive populations, suggesting they may play an etiological role in the development of depression/despair-related processes. Thus, we conducted a series of experiments to determine whether agents known to suppress cytokine activity or inflammatory responses in the CNS would alter the normal progression of behavioral responses during the forced swim test (FST, an animal model of depression/behavioral despair). Adult male Sprague-Dawley rats were injected with indomethacin (1 or 10 mg/kg intraperitoneally (i.p.)), alpha-MSH (0.25 or 0.5 microg icv), or minocycline (20 or 40 mg/kg i.p.) prior to each day of the FST and behavioral assessments were performed. Injection of indomethacin, alpha-MSH, or minocycline had no effect on the development of the immobility response during the FST on either day of testing. In a second series of experiments, we examined whether behavioral responses during forced swim would be affected by acute illness induced by a single injection of lipopolysaccharide (LPS). Acute injection of LPS (10 or 100 microg/kg i.p.) had no effect on behavioral responding during the FST irrespective of when it was injected, despite pronounced reductions in social behavior following these same doses of LPS. From these studies, we conclude that (a) endogenous inflammatory mediators do not appear to be involved in the normal progression of behavioral responses during the FST, and (b) behavioral responses during the FST are not affected by acute systemic injection of LPS.

Changes in ear-pinna temperature as a useful measure of stress in sheep (Ovis aries)

Activation of the sympathetic nervous system, with associated increases in heart rate and the redistribution of blood in preparation for ‘fight or flight’, is an integral part of the ‘defence reaction’. In sheep, the defence reaction involves vasoconstriction in the ear-pinna. If decreases in ear-pinna temperature (Tp) can be used to indicate vasoconstriction, then it may be possible to use changes in Tp as a measure of the defence reaction. Ewe lambs were exposed to stressors including mustering into pens, moving between pens, isolation from conspecifics, and prolonged periods of exercise. Measurements of heart rate (HR), Tp, vaginal temperature (Tv), and salivary cortisol and urinary catecholamine concentrations were used to assess stress responses. A repeatable pattern of changes in HR, Tp and Tv was observed in response to stressors. Short-term disturbances resulted in increased HR, reduced Tp, and increased Tv. More sustained disturbances — for example, prolonged periods of exercise — resulted in a sustained elevation in HR, a sustained decrease in Tp, and a sustained elevation in Tv. The highest levels of cortisol and catecholamines were associated with the treatments that resulted in the longest periods of decreased Tp. We infer that changes in Tp occur largely in response to changes in sympathetic nervous activity, and that the potential exists to measure elements of stress responses by monitoring Tp in freely behaving animals. This is a minimally invasive measure that allows the monitoring of modest numbers of animals over prolonged periods with minimal handling.

Impaired febrile responses to immune challenge in mice deficient in microsomal prostaglandin E synthase-1

Fever is a common, centrally elicited sign of inflammatory and infectious processes and is known to be induced by the action of PGE2 on its specific receptors in the thermogenic region of the hypothalamus. In the present work, using genetically modified mice, we examined the role of the inducible terminal PGE2-synthesizing enzyme microsomal prostaglandin E synthase-1 (mPGES-1) for the generation of immune-elicited fever. Animals with a deletion of the Ptges gene, which encodes mPGES-1, or their wild-type littermates were given either a subcutaneous injection of turpentine--a model for aseptic cytokine-induced pyresis--or an intraperitoneal injection of interleukin-1beta. While both procedures resulted in typical febrile responses in wild-type animals, these responses were strongly impaired in the mPGES-1 mutant mice. In contrast, both genotypes showed psychogenic stress-induced hyperthermia and displayed normal diurnal temperature variations. Both wild-type and mPGES-1 mutant mice also showed strongly reduced motor activity following turpentine injection. Taken together with previous observations on mPGES-1 induction in the brain vasculature during various inflammatory conditions and its role in endotoxin-induced pyresis, the present findings indicate that central PGE2 synthesis by mPGES-1 is a general and critical mechanism for fever during infectious and inflammatory conditions that is distinct from the mechanism(s) underlying the circadian temperature regulation and stress-induced hyperthermia, as well as the inflammation-induced activity depression.

Lesions of the anteroventral third ventricle region (AV3V) disrupt cardiovascular responses to an elevation in core temperature

Blood flow is redistributed from the viscera to the periphery during periods of heat stress to maximize heat loss. The heat-induced redistribution of blood flow is strongly influenced by nonthermal inputs such as hydration status. At present, little is known about where thermal and nonthermal information is integrated to generate an appropriate effector response. Recently, the periventricular tissue that surrounds the anteroventral third ventricle (AV3V) has been implicated in the integration of thermal and osmotic information. The purpose of the present study was to determine the effects of electrolytic lesions of the AV3V on the cardiovascular response to a passive heat stress in unanesthetized, free-moving male Sprague-Dawley rats. Core temperature was elevated at a constant rate of approximately 0.03 degrees C/min in sham- and AV3V-lesion rats using an infrared heat lamp. Changes in mesenteric and hindquarter vascular resistance were determined using Doppler flow probes, and heat-induced salivation was estimated using the spit-print technique. The rise in mean arterial pressure (MAP), heart rate (HR), and mesenteric resistance in response to elevations in core temperature were all attenuated in AV3V-lesion rats; however, hindquarter resistance was unaffected. Heat-induced salivation was also diminished. In addition, AV3V-lesion rats were more affected by the novelty of the experimental environment, resulting in a higher basal core temperature, HR, and MAP. These results indicate that AV3V lesions disrupt the cardiovascular and salivatory response to a passive heat stress in rats and produce an exaggerated stress-induced fever triggered by a novel environment.

Stress-induced increases in hypothalamic IL-1: a systematic analysis of multiple stressor paradigms

Exposure to stressors such as footshock, tailshock, and immobilization have been shown to induce hypothalamic IL-1 production, while other stressors such as restraint, maternal separation, social isolation, and predator exposure have no effect on hypothalamic IL-1 levels. This disparity of findings has led to considerable controversy regarding the ability of stressors to induce hypothalamic IL-1 expression. Thus, the goal of the following experiments was to examine hypothalamic IL-1 responses in adult male Sprague-Dawley rats following exposure to a diverse set of stressors. Our data indicate that exposure to 2h of restraint in a Plexiglas tube, glucoprivic challenge induced by administration of 2-deoxyglucose (2-DG), or insulin-induced hypoglycemia all fail to alter hypothalamic IL-1 levels despite robust activation of the pituitary-adrenal response. However, when restraint was administered on an orbital shaker or in combination with insulin-induced hypoglycemia, robust increases in hypothalamic IL-1 were observed. No effects of glucoprivic (2-DG) challenge were observed when combined with restraint, indicating some specificity in the hypothalamic IL-1 response to stress. We also provide a preliminary validation of the ELISA detection method for IL-1, showing that (a) Western blot analyses confirmed strong immunopositive banding at the apparent molecular weight of both mature IL-1beta and the IL-1beta prohormone, and (b) footshock led to a two-fold increase in mRNA for IL-1 in the hypothalamus as detected by RT-PCR. These data provide novel insight into the characteristics of a stressor that may be necessary for the observation of stress-induced increases in hypothalamic IL-1.

Stress-induced fever after postischemic rectal temperature measurements in the gerbil

Postischemic temperature, which modulates brain injury, is commonly determined via a rectal temperature (Trec) probe. This procedure causes a stress-induced fever (SIF) in rodents that may aggravate injury or diminish the efficacy of a neuroprotectant. We continually measured core temperature (Tcore) via an implanted telemetry probe and made 16 Trec measurements over 4 days in sham and ischemic gerbils (5 min bilateral carotid artery occlusion). Controls did not have Trec sampled, but Tcore was measured. Rectal temperature measurements predicted Tcore in sham and ischemic gerbils. The Trec measurements caused a SIF (1 degrees C peak) in shams that did not habituate, whereas the SIF was initially absent and then increased over days in ischemic gerbils. Ischemic groups had similar CA1 injury (approximately 32% remaining), presumably because Trec measurements only resulted in a significant SIF starting on day 2 postischemia, when cell death is less sensitive to hyperthermia. Caution is warranted with Trec measurements, since the resultant SIF occurs to different extents in normal and ischemic rodents. Furthermore, the SIF could vary according to many other factors, such as the type and severity of insult, the time and frequency of measurement, and drug treatment. Accordingly, postischemic Trec measurements should be replaced with telemetry probes.