Effect of intracerebroventricular administration of vasopressin on stress-induced hyperthermia in rats

Body surface temperature of rats reveals both magnitude and sex differences in the acute stress response

Understanding how biological markers of stress relate to stressor magnitude is much needed and can be used in welfare assessment. Changes in body surface temperature can be measured using infrared thermography (IRT) as a marker of a physiological response to acute stress. While an avian study has shown that changes in body surface temperature can reflect the intensity of acute stress, little is known about surface temperature responses to stressors of different magnitudes and its sex-specificity in mammals, and how they correlate with hormonal and behavioural responses. We used IRT to collect continuous surface temperature measurements of tail and eye of adult male and female rats (Rattus norvegicus), for 30 minutes after exposure to one of three stressors (small cage, encircling handling or rodent restraint cone) for one minute, and cross-validated the thermal response with plasma corticosterone (CORT) and behavioural assessment. To obtain individual baseline temperatures and thermal responses to stress, rats were imaged in a test arena (to which they were habituated) for 30 seconds before and 30 minutes after being exposed to the stressor. In response to the three stressors, tail temperature initially decreased and then recovered to, or overshot the baseline temperature. Tail temperature dynamics differed between stressors; being restrained in the small cage was associated with the smallest drop in temperature, in male rats, and the fastest thermal recovery, in both sexes. Increases in eye temperature only distinguished between stressors early in the response and only in females. The post stressor increase in eye temperature was greater in the right eye of males and the left eye of females. In both sexes encircling may have been associated with the fastest increase in CORT. These results were in line with observed behavioural changes, with greater movement in rats exposed to the small cage and higher immobility after encircling. The female tail and eye temperature, as well as the CORT concentrations did not return to pre-stressor levels in the observation period, in conjunction with the greater occurrence of escape-related behaviours in female rats. These results suggest that female rats are more vulnerable to acute restraint stress compared to male rats and emphasise the importance of using both sexes in future investigations of stressor magnitude. This study demonstrates that acute stress induced changes in mammalian surface temperature measured with IRT relate to the magnitude of restraint stress, indicate sex differences and correlate with hormonal and behavioural responses. Thus, IRT has the potential to become a non-invasive method of continuous welfare assessment in unrestrained mammals.

Oxytocin and 'social hyperthermia': Interaction with β3-adrenergic receptor-mediated thermogenesis and significance for the expression of social behavior in male and female mice

Oxytocin (OT) is a critical regulator of multiple facets of energy homeostasis, including brown adipose tissue (BAT) thermogenesis. Nevertheless, it is unclear what, if any, consequence the thermoregulatory and metabolic effects of OT have for the display of social behavior in adult rodents. Here, we examine the contribution of the OT receptor (OTR) and β₃ adrenergic receptor (β₃AR) to the increase in body temperature that typically accompanies social interaction (i.e., social hyperthermia; SH) and whether SH relates to the expression of social behavior in adult mice. Specifically, we examined how OTR antagonism via peripheral injection of L-368,899 (10 mg/kg) affects the expression of social behavior in C57BL/6J mice, in the presence of active/agonized versus antagonized β₃AR, the receptor known to mediate stress-induced BAT thermogenesis. After drug treatment and a 30 min delay, mice were provided a 10 min social interaction test with an unfamiliar, same-sex conspecific. We hypothesized that OTR and β₃AR/BAT interact to influence behavior during social interaction, with at least some effects of OT on social behavior dependent upon OT's thermal effects via β₃AR/BAT. We found that OTR-mediated temperature elevation is largely responsible for SH during social interaction in mice-albeit not substantially via β₃AR-dependent BAT thermogenesis. Further, our results reveal a complex relationship between OTR, β₃AR, social hyperthermia and the display of specific social behaviors, with SH most closely associated with anxiety and/or vigilance-related behaviors-that is, behaviors that antagonize or interfere with the initiation of close, non-agonistic social behavior.

Physics of mind: Experimental confirmations of theoretical predictions

What is common among Newtonian mechanics, statistical physics, thermodynamics, quantum physics, the theory of relativity, astrophysics and the theory of superstrings? All these areas of physics have in common a methodology, which is discussed in the first few lines of the review. Is a physics of the mind possible? Is it possible to describe how a mind adapts in real time to changes in the physical world through a theory based on a few basic laws? From perception and elementary cognition to emotions and abstract ideas allowing high-level cognition and executive functioning, at nearly all levels of study, the mind shows variability and uncertainties. Is it possible to turn psychology and neuroscience into so-called "hard" sciences? This review discusses several established first principles for the description of mind and their mathematical formulations. A mathematical model of mind is derived from these principles. This model includes mechanisms of instincts, emotions, behavior, cognition, concepts, language, intuitions, and imagination. We clarify fundamental notions such as the opposition between the conscious and the unconscious, the knowledge instinct and aesthetic emotions, as well as humans' universal abilities for symbols and meaning. In particular, the review discusses in length evolutionary and cognitive functions of aesthetic emotions and musical emotions. Several theoretical predictions are derived from the model, some of which have been experimentally confirmed. These empirical results are summarized and we introduce new theoretical developments. Several unsolved theoretical problems are proposed, as well as new experimental challenges for future research.

Entanglement between thermoregulation and nociception in the rat: the case of morphine

In thermoneutral conditions, rats display cyclic variations of the vasomotion of the tail and paws, the most widely used target organs in current acute or chronic animal models of pain. Systemic morphine elicits their vasoconstriction followed by hyperthermia in a naloxone-reversible and dose-dependent fashion. The dose-response curves were steep with ED50 in the 0.5-1 mg/kg range. Given the pivotal functional role of the rostral ventromedial medulla (RVM) in nociception and the rostral medullary raphe (rMR) in thermoregulation, two largely overlapping brain regions, the RVM/rMR was blocked by muscimol: it suppressed the effects of morphine. "On-" and "off-" neurons recorded in the RVM/rMR are activated and inhibited by thermal nociceptive stimuli, respectively. They are also implicated in regulating the cyclic variations of the vasomotion of the tail and paws seen in thermoneutral conditions. Morphine elicited abrupt inhibition and activation of the firing of on- and off-cells recorded in the RVM/rMR. By using a model that takes into account the power of the radiant heat source, initial skin temperature, core body temperature, and peripheral nerve conduction distance, one can argue that the morphine-induced increase of reaction time is mainly related to the morphine-induced vasoconstriction. This statement was confirmed by analyzing in psychophysical terms the tail-flick response to random variations of noxious radiant heat. Although the increase of a reaction time to radiant heat is generally interpreted in terms of analgesia, the present data question the validity of using such an approach to build a pain index.

The sleep-promoting and hypothermic effects of glycine are mediated by NMDA receptors in the suprachiasmatic nucleus

The use of glycine as a therapeutic option for improving sleep quality is a novel and safe approach. However, despite clinical evidence of its efficacy, the details of its mechanism remain poorly understood. In this study, we investigated the site of action and sleep-promoting mechanisms of glycine in rats. In acute sleep disturbance, oral administration of glycine-induced non-rapid eye movement (REM) sleep and shortened NREM sleep latency with a simultaneous decrease in core temperature. Oral and intracerebroventricular injection of glycine elevated cutaneous blood flow (CBF) at the plantar surface in a dose-dependent manner, resulting in heat loss. Pretreatment with N-methyl-D-aspartate (NMDA) receptor antagonists AP5 and CGP78608 but not the glycine receptor antagonist strychnine inhibited the CBF increase caused by glycine injection into the brain. Induction of c-Fos expression was observed in the hypothalamic nuclei, including the medial preoptic area (MPO) and the suprachiasmatic nucleus (SCN) shell after glycine administration. Bilateral microinjection of glycine into the SCN elevated CBF in a dose-dependent manner, whereas no effect was observed when glycine was injected into the MPO and dorsal subparaventricular zone. In addition, microinjection of D-serine into the SCN also increased CBF, whereas these effects were blocked in the presence of L-701324. SCN ablation completely abolished the sleep-promoting and hypothermic effects of glycine. These data suggest that exogenous glycine promotes sleep via peripheral vasodilatation through the activation of NMDA receptors in the SCN shell.

The nonpeptide oxytocin receptor agonist WAY 267,464: receptor-binding profile, prosocial effects and distribution of c-Fos expression in adolescent rats

Previous research suggests that the nonpeptide oxytocin receptor (OTR) agonist WAY 267,464 may only partly mimic the effects of oxytocin in rodents. The present study further explored these differences and related them to OTR and vasopressin 1a receptor (V(1a) R) pharmacology and regional patterns of c-Fos expression. Binding data for WAY 267,464 and oxytocin were obtained by displacement binding assays on cellular membranes, while functional receptor data were generated by luciferase reporter assays. For behavioural testing, adolescent rats were tested in a social preference paradigm, the elevated plus-maze (EPM) and for locomotor activity changes following WAY 267,464 (10 and 100 mg/kg, i.p.) or oxytocin (0.1 and 1 mg/kg, i.p.). The higher doses were also examined for their effects on regional c-Fos expression. Results showed that WAY 267,464 had higher affinity (K(i) ) at the V(1a) R than the OTR (113 versus 978 nm). However, it had no functional response at the V(1a) R and only a weak functional effect (EC(50) ) at the OTR (881 nm). This suggests WAY 267,464 is an OTR agonist with weak affinity and a possible V(1a) R antagonist. Oxytocin showed high binding at the OTR (1.0 nm) and V(1a) R (503 nm), with a functional EC(50) of 9.0 and 59.7 nm, respectively, indicating it is a potent OTR agonist and full V(1a) R agonist. WAY 267,464 (100 mg/kg), but not oxytocin, significantly increased the proportion of time spent with a live rat, over a dummy rat, in the social preference test. Neither compound affected EPM behaviour, whereas the higher doses of WAY 267,464 and oxytocin suppressed locomotor activity. WAY 267,464 and oxytocin produced similar c-Fos expression in the paraventricular hypothalamic nucleus, central amygdala, lateral parabrachial nucleus and nucleus of the solitary tract, suggesting a commonality of action at the OTR with the differential doses employed. However, WAY 267,464 caused greater c-Fos expression in the medial amygdala and the supraoptic nucleus than oxytocin, and lesser effects in the locus coeruleus. Overall, our results confirm the differential effects of WAY 267,464 and oxytocin and suggest that this may reflect contrasting actions of WAY 267,464 and oxytocin at the V(1a) R. Antagonism of the V(1a) R by WAY 267,464 could underlie some of the prosocial effects of this drug either through a direct action or through disinhibition of oxytocin circuitry that is subject to vasopressin inhibitory influences.

Sex differences in stress-induced hyperthermia in rats: restraint versus confinement

Studies using restraint to induce psychological stress consistently report the expected hyperthermic response in core body temperature (CBT), but many also report a hypothermic response that precedes the hyperthermia. To understand the conditions that produce hypothermia, and to study sex differences in stress-induced hyperthermia, we measured CBT in male and female rats at 70 and 180 days of age in response to two types of stressors: immobilization through restraint (Plexiglas restrainer) and confinement in a small area (circular wire mesh cylinders that allowed free airflow). Restraint early in the light period induced hypothermia only in 180-day-old males, with no hyperthermia observed during the 30-minute restraint period. Increases in humidity and temperature of the microenvironment due to the larger body weight at this age may contribute to the hypothermia. Hyperthermia during restraint in 70-day-old males was significantly attenuated and delayed in onset compared to the rise in females. All females exhibited a CBT rise of approximately 1.3 degrees C occurring 10-15 min after the onset of restraint. Restraint early in the dark period induced no significant change in CBT in males of either age during immobilization, while females exhibited a small rise of approximately 0.5 degrees C. Confinement early in the light period induced a significant rise of approximately 1.5 degrees C in all groups, with no preceding hypothermia. However, the male response was significantly delayed compared to females. Overall, these results indicate that CBT changes during restraint likely involve both anxiogenic and physiological components, while the marked hyperthermia during confinement is primarily psychological in both sexes.

Selective blockade of 5-HT2A receptors attenuates the increased temperature response in brown adipose tissue to restraint stress in rats

Previous studies have demonstrated that 5-HT2A receptors may be involved in the central control of thermoregulation and of the cardiovascular system. Our aim was to test whether these receptors mediate thermogenic and tachycardiac responses induced by acute psychological stress. Three groups of adult male Hooded Wistar rats were instrumented with: (i) a thermistor in the interscapular area (for recording brown adipose tissue temperature) and an ultrasound Doppler probe (to record tail blood flow); (ii) temperature dataloggers to record core body temperature; (iii) ECG electrodes. On the day of the experiment, rats were subjected to a 30-min restraint stress preceded by s.c. injection of either vehicle or SR-46349B (a serotonin 2A receptor antagonist) at doses of 0.01, 0.1 and 1.0 mg/kg. The restraint stress caused a rise in brown adipose tissue temperature (from, mean +/- s.e.m., 36.6 +/- 0.2 to 38.0 +/- 0.2 degrees C), transient cutaneous vasoconstriction (tail blood flow decreased from 12 +/- 2 to 5 +/- 1 cm/s), increase in heart rate (from 303 +/- 15 to 453 +/- 15 bpm at the peak, then reduced to 393 +/- 12 bpm at the steady state), and defaecation (6 +/- 1 pellets per restraint session). The core body temperature was not affected by the restraint. Blockade of 5-HT2A receptors attenuated the increase in brown adipose tissue temperature and transient cutaneous vasoconstriction, but not tachycardia and defaecation elicited by restraint stress. These results indicate that psychological stress causes activation of 5-HT2A receptors in neural pathways that control thermogenesis in the brown adipose tissue and facilitate cutaneous vasoconstriction.

Role of locus coeruleus heme oxygenase-carbon monoxide-cGMP pathway during hypothermic response to restraint

Central heme oxigenase-carbon monoxide (HO-CO) pathway has been shown to play a pyretic role in the thermoregulatory response to restraint. However, the specific site in the central nervous system where CO may act modulating this response remains unclear. LC is rich not only in sGC but also in heme oxygenase (HO; the enzyme that catalyses the metabolism of heme to CO, along with biliverdin and free iron). Therefore, the possible role of the HO-CO-cGMP pathway in the restraint-induced-hypothermia by LC neurons was investigated. Body temperature dropped about 0.7 degrees C during restraint. ZnDPBG (a HO inhibitor; 5 nmol, intra-LC) prevented the hypothermic response during restraint. Conversely, induction of the HO pathway in the LC with heme-lysinate (7.6 nmol, intra-LC) intensified the hypothermic response to restraint, and this effect was prevented by pretreatment with ODQ (a sGC inhibitor; given intracerebroventricularly, 1.3 nmol). Taken together, these data suggest that CO in the LC produced by the HO pathway and acting via cGMP is implicated in thermal responses to restraint.

Effects of intracerebroventricular infusions of arginine vasopressin in sheep

In sheep, neither the in vivo effect of vasopressin administered by a method other than systemic infusion nor the central effects on behavior from the perspective of stress regulation has been fully elucidated in an intact animal. We examined changes in behavioral, adrenocorticotropic, and autonomic nervous functions after intracerebroventricular infusions of arginine vasopressin (AVP) to elucidate its central role. Intracerebroventricular infusions of AVP (0, 0.12, 1.2 and 12 microg/500 microl/30 min) evoked a dose-related increase in plasma cortisol concentration. There were significant treatment-related effects on the total duration of sham-chewing (Friedman's test, X2=12.75, p=.0052), on the total duration of bar-biting (Friedman's test, X2=15.0, p=.0018), and on the total duration of rubbing (Friedman's test, X2=12.0, p=.0074). AVP 12 microg treatment induced a greater degree of sham-chewing and bar-biting than the other three treatments did (Nemenyi multiple comparisons: p<0.1). These findings indicate, together with our previous findings, that AVP has the same corticotropic potential as corticotropin-releasing hormone infused intracerebroventricularly in equal molar concentrations. Although the degree to which central stress signaling pathways are involved in these responses remains speculative, the relationships between stereotypies and central AVP are of particular interest.

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.

Central nNOS is involved in restraint stress-induced fever: evidence for a cGMP pathway

It has been shown that the NO pathway plays a major role in restraint stress-induced fever, and that the neuronal nitric oxide synthase (nNOS) seems to be the NOS isoform that accounts for the pyretic effect of NO in psychological stress-induced fever. However, no information exists as to localization of the nNOS, i.e., in the peripheral or in the central nervous system (CNS). Thus, in the present study, we tested the hypothesis that NO arising from nNOS in the CNS participates in restraint stress-induced fever. Moreover, we also assessed the involvement of cyclic guanosine monophosphate (cGMP) in the mediation of the NO effects. To this end, intracerebroventricular S-methyl-L-thiocitrulline (SMTC; a selective nNOS inhibitor), sodium nitroprusside (an NO donor) or Rp-guanosine 3',5'-cyclic monophosphothioate triethylamine (Rp-cGMPS; a specific membrane-permeable inhibitor of the activation by cGMP of cGMP-dependent protein kinase) were injected, and the colonic temperature (T(c)) of restrained or unrestrained rats was recorded. Both SMTC (0.5 mg/mul) and Rp-cGMPS (10 mug/mul) intracerebroventricular injections enhanced restraint fever, whereas intracerebroventricular injections of sodium nitroprusside (100 mug/mul) reduced this response. These data indicate that NO produced in the CNS, arising from nNOS and acting via cGMP, plays an antipyretic role in the restraint stress-induced fever.

Role of the brain heme oxygenase-carbon monoxide pathway in stress fever in rats

This study was aimed at testing the hypothesis that the brain heme oxygenase (HO)-carbon monoxide (CO) pathway plays a role in stress fever. To this end, the effect of the HO inhibitor, zinc deuteroporphyrin 2,4-bis glycol (ZnDPBG), on restraint-induced fever was tested. Intracerebroventricular ZnDPBG (200 nmol) did not affect the body core temperature of unrestrained rats, but markedly attenuated restraint-induced fever. However, at the same dose, intraperitoneal ZnDPBG did not affect the febrile response to restraint. Taken together, these results indicate that the brain HO-CO pathway plays a major role in the genesis of stress fever in rats.

Possible role of vasopressin in the thermoregulatory response to chlorpyrifos in the rat

Arginine vasopressin is a naturally occurring antipyretic which is released into the CNS to prevent excessive elevations in body temperature during fever. Circulating levels of arginine vasopressin may also have a role in the tonic control of body temperature. We have found that the organophosphate insecticide chlorpyrifos will raise blood pressure and lower body temperature in the rat. Because arginine vasopressin is a potent hypertensive agent and is capable of lowering core temperature, we suspected that arginine vasopressin may be involved in the thermoregulatory response to chlorpyrifos. To this end, core temperature and motor activity of male and female Sprague-Dawely rats were monitored before and after treatment with the corn oil vehicle or chlorpyrifos (15 mg/kg in females; 30 mg/kg in males; oral) concomitant with injection of a saline vehicle or a type 1 arginine vasopressin antagonist (20 microg/kg in females; 30 microg/kg in males; intraperitoneally). Rats dosed with chlorpyrifos and saline underwent a 2-3 degrees reduction in core temperature >50% decrease in motor activity. The V1 antagonist attenuated the hypothermic effect of chlorpyrifos in both sexes. Chlorpyrifos-induced inhibition in motor activity was unaffected by the V1 antagonist. In another experiment, the V1 antagonist (30 microg/kg) was co-administered with saline or 0.2 mg/kg oxotremorine, a muscarinic agonist that stimulates a heat loss response and partially mimics the effects of chlorpyrifos. The V1 antagonist attenuated the hypothermic effect of oxotremorine in both sexes. Plasma arginine vasopressin levels were determined in male rats 3 hr after corn oil or 30 mg/kg chlorpyrifos. There was no significant effect of chlorpyrifos on plasma levels of arginine vasopressin. That the V1 antagonist blocked the hypothermic effect of chlorpyrifos suggests that the thermoregulatory response to chlorpyrifos is mediated by central and/or systemic vasopressin release. The lack of a significant increase in plasma vasopressin after chlorpyrifos suggests that localized release of vasopressin may be involved in the thermoregulatory response to chlorpyrifos.

Altered forebrain neurotransmitter responses to immobilization stress following 3,4-methylenedioxymethamphetamine

(+/-)3,4-Methylenedioxymethamphetamine (MDMA, "ecstasy") is an increasingly popular drug of abuse that acts as a neurotoxin to forebrain serotonin neurons. The neurochemical effects of the serotonin depletion following high doses of MDMA were investigated in response to acute immobilization stress. Male rats were treated with a neurotoxic dosing regimen of MDMA (10 mg/kg, i.p. every 2 h for four injections) or equivalent doses of saline. Seven days after treatment, in vivo microdialysis was used to assess extracellular dopamine and serotonin in the dorsal hippocampus and prefrontal cortex during 1 h of immobilization stress. In saline treated control rats, serotonin in the hippocampus and serotonin and dopamine in the prefrontal cortex were increased during immobilization stress. Rats pretreated with MDMA, however, showed blunted neurotransmitter responses in the hippocampus and the prefrontal cortex. In the drug pretreated rats, basal serotonin levels in the hippocampus, but not the prefrontal cortex, were lower compared to saline pretreated controls. Stress-induced increases in plasma corticosterone and body temperature were not affected by the pretreatment condition. From these studies we suggest that depletion of serotonin stores in terminal regions with the neurotoxin MDMA compromises the ability of the serotonergic neurons to activate central systems that respond to stressful stimuli. This altered responsiveness may have implications for long-term functional consequences of MDMA abuse as well as the interactions between the serotonergic system and stress.

Stress-induced hyperthermia depends on both time of day and light condition

Rats placed in an environment other than their home cage increase their body temperature (Tb) by more than 1 degree C. This stress-induced hyperthermia is considered to be a fever, in the sense that the Tb rise seems to reflect an upward shift in the level of regulated Tb (set point). The circadian rhythm of Tb also reflects changes in set point. One might therefore expect to see differences in response to such stress during various phases of the light-dark (LD) cycle as Tb fluctuates between L and D. To test this, 3- to 6-month-old male Long-Evans rats were taken from their home cages (12:12 LD) and placed individually in a Plexiglas container for 30 min. Tb and activity were measured via telemetry. In the first experiment, rats were placed in the container during day (from 1 to 3 h after lights on) and night (from 1 to 3 h after lights off), with light on or off during the test. There was a significant Tb rise in response to placement in the container at all times except when the rats were tested during the night with light on in the container; in that condition there was no Tb rise. In the second experiment, the authors determined that 30 min of light in the home cage before the test did not affect Tb: If the light was on in the test situation, hyperthermia was inhibited, and if it was off, hyperthermia was as high as control levels. In the third experiment, to determine whether this effect was time dependent, the test was performed at 4-h intervals, with light on or off during the test. The strongest inhibiting effect of light was in early night. In the fourth experiment, the authors turned the lights on during early night while the rats were in their home cages. This reduced their Tb significantly by less than 0.3 degrees C. The authors conclude that both clock time and light condition during testing are factors affecting the Tb rise in response to stress.

Alleviating effects of plant-derived fragrances on stress-induced hyperthermia in rats

In the present study, the effects of exposure to plant-derived odors on the autonomic and behavioral responses to novel environment were examined in rats. Male rats (n=42) carrying a telemetry transmitter were individually housed, and on the test day each rat was transferred to a new cage containing bedding that had been sprayed immediately before testing with 200 microl of 0.03% dilution of either lavender essential oil, green leaf odor (a mixture of hexenol and hexenal), alpha-pinene, or solvent (triethyl citrate) as a control. Following the transfer to this novel environment, the body temperature of the rats increased by nearly 1 degrees C, showing a stress-induced hyperthermia. Stress-induced hyperthermia was attenuated by the green odor and the alpha-pinene, but not by the lavender or solvent. There was no clear effect of fragrances on heart rate or behavioral responses. These results suggest that plant-derived fragrances, such as green odor and alpha-pinene, have calming effects on autonomic stress response to novel environments.

Involvement of neuronal nitric oxide synthase in restraint stress-induced fever in rats

Nitric oxide (NO) has been shown to be an important modulator of the febrile response to pyrogens and to psychological stress. In the present study, we aimed to identify the nitric oxide synthase (NOS) isoform (neuronal or inducible, nNOS and iNOS, respectively) involved in restraint stress fever. Colonic temperature (Tc) was measured in unanesthetized rats before and after treatment with the more selective nNOS inhibitor 7-nitroindazole or with the selective iNOS inhibitor aminoguanidine (AG) under unrestrained or restrained conditions. Intraperitoneal injection of AG (25 or 50 mg/kg) did not affect restraint fever, indicating that iNOS is unlikely to be involved in restraint fever. On the other hand, intraperitoneal injection of 7-nitroindazole (25 mg/kg) significantly attenuated the rise in the Tc caused by restraint stress, whereas it caused no change in Tc of euthermic animals. These data show that NO produced by nNOS plays an important role in the genesis of restraint stress-induced fever.

Paradoxical effects of chronic morphine treatment on the temperature and pituitary-adrenal responses to acute restraint stress: a chronic stress paradigm

Body temperature and pituitary-adrenal responses to restraint (15 min or 4 h) stress were evaluated in nondependent and morphine-dependent rats. Male Sprague-Dawley rats were treated twice daily with increasing doses of morphine (10-100 mg/kg, s.c.) for 16 days. Transmitters were implanted in the peritoneal cavity to monitor body temperature and blood was collected for hormone assays. Acute withdrawal from chronic morphine treatment was associated with reduced body weight, increased adrenal weight and decreased thymus weight. Sixteen days after termination of chronic morphine treatment, rats had recovered normal adrenal size, but still displayed marked thymus involution and reduced body weight. Restraint-induced hyperthermia was attenuated in morphine-dependent rats that had undergone 12-h withdrawal. Sixteen days after withdrawal, rats still had not fully recovered the hyperthermic response to restraint. Chronic morphine treatment resulted in a marked elevation of basal corticosterone concentrations. Despite the negative-feedback effects of elevated basal corticosterone concentrations, morphine-dependent rats that had undergone 12-h withdrawal displayed a potentiated and prolonged corticosterone response to restraint stress. In contrast, rats that had undergone 8-day and 16-day morphine withdrawal had recovered normal basal pituitary-adrenal activity, but displayed significantly reduced and shorter adrenocorticotropic hormone and corticosterone responses to restraint. These results suggest that chronic morphine dependence is a chronic stressor, resulting in profound and long-lasting changes in the temperature and pituitary-adrenal responses to acute restraint stress in a time-dependent manner. This morphine-dependence model may be useful in understanding the role that hormonal stress responses play in the maintenance and relapse to opioid use in humans.

Neuroprotective effects of mild hyperthermia prior to focal ischemia in conscious rats

Hyperthermia during or after stroke is known to worsen neuronal damage. Paradoxically, when hyperthermia precedes stroke, it can protect against a subsequent ischemic insult. Other stressors including restraint also have a similar pre-conditioning effect. In the present study, we report the unanticipated finding that conscious rats, restrained for the purpose of intravenous infusion, had markedly reduced neuronal and functional deficits after middle cerebral artery occlusion compared with unrestrained rats. Restrained rats had significantly higher body temperature prior to stroke than unrestrained rats. The findings suggest restraint leading to mild hyperthermia may be sufficient to induce adaptive processes which protect against subsequent ischemia.

Endogenous antipyretics

Fever is the hallmark of the stereotyped host response to microbial infection, although it is just one of a number of high-risk strategies employed by the infected host to clear itself of invading pathogens. The febrile response is accompanied by activation of multiple endogenous antipyretic systems that serve to suppress its magnitude or duration. These include neuroactive substances of neural and humoral origin, some of which (e.g., glucocorticoids, melanocortins, and IL-10) have broad-ranging anti-inflammatory actions. Glucocorticoids, vasopressin, and melanocortins appear to exert their antipyretic effects by acting on receptors within the brain, but beyond this the mechanisms involved are unknown. It is hypothesized, but not proven, that endogenous antipyretic systems protect the host against the destructive consequences of unchecked fever. Importantly, pharmacological blockade of the actions of endogenous antipyretic systems increases fevers of even low to moderate intensity. Therefore, in addition to protecting against catastrophic consequences of high fever, endogenous antipyretic systems seem to play a fundamental physiological role in determining the normal course of fever. Elucidating the neural and biochemical mechanisms involved in suppression of fever by physiological antipyretic systems will yield a rich benefit, both by advancing the basic understanding of host defense strategies, and by permitting the design of novel antipyretic and anti-inflammatory strategies for therapeutic intervention in human disease.

The nitric oxide pathway is an important modulator of stress-induced fever in rats

Psychological stress evokes a number of physiological responses, including a rise in body temperature (T(b)), which has been suggested to be the result of an elevation in the thermoregulatory set point, i.e., a fever. This response seems to share similar mechanisms with infectious fever. A growing number of studies have provided evidence that nitric oxide (NO) has a modulatory role in infectious fever, but no report exists about the participation of NO in stress fever. Thus, the present study aimed to verify the hypothesis that NO modulates stress fever by using restraint stress as a model. To this end, we tested the effects of the non-specific NO synthase (NOS) inhibitor N(G)-nitro-L-arginine methyl ester (L-NAME) or its inactive enantiomer N(G)-nitro-D-arginine methyl ester (D-NAME) on colonic T(b) of restrained or unrestrained rats. A rapid increase in T(b) was observed when animals were submitted to restraint. Intravenous (i.v.) injection of L-NAME at a dose (10 mg/kg) that caused no change in T(b) when administered alone significantly attenuated the elevation in T(b) elicited by stress, indicating that the NO pathway may mediate stress fever. Moreover, intracerebroventricular (i.c.v.) L-NAME (250 microg/microl) caused a rise in T(b) of euthermic animals and enhanced stress fever, supporting that NO in the central nervous system (CNS) leads to a reduction in T(b) and, therefore, this is unlikely to be the site where NO may mediate stress fever. Taken together, these data indicate that the NO pathway plays an important role in modulating restraint stress-induced fever in rats.

Restraint as a stressor in mice: against the dopaminergic neurotoxicity of D-MDMA, low body weight mitigates restraint-induced hypothermia and consequent neuroprotection

In experimental studies of stress, restraint of laboratory rodents, perceived as easy to apply and believed to be reproducible, is a commonly used manipulation. The restraint manipulation is utilized as a technique to characterize the physiological, cellular and molecular consequences of stress as well as a tool to understand the ways in which stress may interact with toxic substances. In previous work, we utilized restraint in an examination of the effect of stress on the striatal dopaminergic neurotoxicity engendered by a series of substituted amphetamines. Contrary to our expectations, and most likely due to its body temperature-reducing properties in the mouse, restraint provided total or near total protection against the neurotoxicity of these agents. During subsequent studies utilizing C57Bl6/J female mice of varying weights and ages the degree of temperature reduction and the associated ability to block (20-100%) the dopamine depletion associated with the neurotoxic amphetamine 3,4-methylendioxyamphetamine (D-MDMA, 20 mg/kg of mouse body weight, every 2 h, s.c., total of four doses) were found to vary considerably more than had been previously observed. An in-depth analysis of the role mouse weight plays in the temperature reduction induced by restraint indicates mouse weight is a primary determinant of hypothermia and subsequent neuroprotection. It suggests the induction of stress in rodents by restraint is a complex effect that may lead to unanticipated results. The restraint manipulation is not as straight-forward a procedure as is commonly believed. Our data indicate that consistent application of restraint may require an adjustment of the restrainer device to mouse body weight.

Role of AVP in mediating the altered core temperature response to a simulated open field in pregnant rats

Near the term of pregnancy, rats have an attenuated core temperature response on exposure to a novel environment (e.g., a simulated open field) compared with that observed early in pregnancy or in nonpregnant rats. The present experiments were carried out on 26 nonpregnant and 26 pregnant rats to test the hypothesis that arginine vasopressin, functioning as an endogenous antipyretic substance in the central nervous system, mediates this attenuated core temperature response. Exposure to a simulated open field after intracerebroventricular (ICV) vehicle produced a significant increase in core temperature in both nonpregnant and pregnant animals, the magnitude and duration of which were greater in the nonpregnant rats. In nonpregnant rats, exposure to a simulated open field after ICV vasopressin V(1)-receptor antagonist altered the pattern of the core temperature response but not the core temperature index compared with that observed on exposure to a simulated open field after ICV vehicle. In pregnant animals, ICV vasopressin V(1)-receptor antagonist did not alter the core temperature response to a simulated open field compared with that observed after ICV vehicle. Thus our data do not support the hypothesis that a pregnancy-related activation of arginine vasopressin attenuates the core temperature response to a simulated open field in rats near the term of pregnancy.

Arginine vasopressin, fever and temperature regulation

While central administration of arginine vasopressin (VP) to the non-febrile rat at high doses can cause hypothermia, there is little evidence for a role for endogenous VP in normal thermoregulation. In contrast, VP arising from cell bodies in the bed nucleus of the stria terminalis and innervating the ventral septal areas and possibly the amygdala appears to be an endogenous antipyretic, i.e. a substance capable of reducing fever. As the synthesis of VP in bed nucleus neurons is dependent upon circulating androgens, female rats have much less VP in these cells and their projections than do male rats. In keeping with this, females may make use of VP to a lesser extent than do males to bring about antipyresis. The phenomenon whereby the VP receptor can become sensitized by previous exposure to VP may be responsible for some states of endogenous antipyresis, in which fevers are suppressed through overactivity of the vasopressinergic system. States of endogenous antipyresis can be revealed around the time of parturition in both the neonate and the mother.

Vasopressin released within the septal brain area during swim stress modulates the behavioural stress response in rats

The aim of the present study was to investigate the physiological significance of the neuropeptide arginine vasopressin (AVP) released within the septum, in the behavioural response of rats to stress. In the first experiment, rats were chronically implanted with a microdialysis probe aimed at the mediolateral or ventral septum to monitor the local release of AVP in response to 10 min of forced swimming in 20 degrees C warm water. Exposure to this stressor caused a significant increase in AVP release in both the mediolateral (174 +/- 21%, P < 0.01) and ventral septum (220 +/- 33%, P < 0.01). In contrast, microdialysates collected outside the mediolateral septum or in the lateral ventricle remained at prestress levels throughout the dialysis period. Furthermore, unstressed control animals failed to show significant alterations in vasopressin release in the mediolateral septum. In a second experiment, the introduction of the V1 receptor antagonist d(CH2)5Tyr(Me)AVP into the mediolateral septum via inverse microdialysis concomitant with stressor exposure caused the rats to spend an increased time floating and a reduced time swimming compared to vehicle-treated rats. This effect was acute and also detected 24 h after antagonist administration. Taken together, these findings demonstrate a significant activation of the septal vasopressinergic system in response to swim stress. Furthermore, our data support the view that AVP released within this brain area is involved in the generation of active behavioural strategies aimed at coping with new and challenging situations.

Effects of transport and indomethacin on telemetered body temperature and release of cortisol and prolactin in pre-pubertal pigs

Previous research indicates that acute physical stress (restraint) raises core temperature in growing pigs via a prostaglandin-dependent mechanism. This study investigated whether transport stress affects body temperature in pigs and whether any such changes might involve endogenous prostaglandins. Pre-pubertal boars (n = 7) were implanted with venous catheters and biotelemetry devices for the measurement of core temperature. They were transported for two hours, with and without indomethacin (IND) pre-treatment, and blood samples were taken at 15 minute intervals for the determination of plasma cortisol and prolactin concentrations. The results indicated that, contrary to predictions, body temperature tended to fall during transport and that the effect was exaggerated by IND. By contrast, cortisol concentrations increased during transport and were unaffected by IND whereas the tendency for transport to stimulate prolactin release was reversed by IND.