A New Concept of Temperature Regulation by Amines in the Hypothalamus

Traumatic brain injury extending to the striatum alters autonomic thermoregulation and hypothalamic monoamines in recovering rats

The brain cortex is the structure that is typically injured in traumatic brain injury (TBI) and is anatomically connected with other brain regions, including the striatum and hypothalamus, which are associated in part with motor function and the regulation of body temperature, respectively. We investigated whether a TBI extending to the striatum could affect peripheral and core temperatures as an indicator of autonomic thermoregulatory function. Moreover, it is unknown whether thermal modulation is accompanied by hypothalamic and cortical monoamine changes in rats with motor function recovery. The animals were allocated into three groups: the sham group (sham), a TBI group with a cortical contusion alone (TBI alone), and a TBI group with an injury extending to the dorsal striatum (TBI + striatal injury). Body temperature and motor deficits were evaluated for 20 days post-injury. On the 3rd and 20th days, rats were euthanized to measure the serotonin (5-HT), noradrenaline (NA), and dopamine (DA) levels using high-performance liquid chromatography (HPLC). We observed that TBI with an injury extending to the dorsal striatum increased core and peripheral temperatures. These changes were accompanied by a sustained motor deficit lasting for 14 days. Furthermore, there were notable increases in NA and 5-HT levels in the brain cortex and hypothalamus both 3 and 20 days after injury. In contrast, rats with TBI alone showed no changes in peripheral temperatures and achieved motor function recovery by the 7th day post-injury. In conclusion, our results suggest that TBI with an injury extending to the dorsal striatum elevates both core and peripheral temperatures, causing a delay in functional recovery and increasing hypothalamic monoamine levels. The aftereffects can be attributed to the injury site and changes to the autonomic thermoregulatory functions.

5-HT Receptors and Temperature Homeostasis

The present review summarizes the data concerning the influence of serotonin (5-HT) receptors on body temperature in warm-blooded animals and on processes associated with its maintenance. This review includes the most important part of investigations from the first studies to the latest ones. The established results on the pharmacological activation of 5-HT1A, 5-HT3, 5-HT7 and 5-HT2 receptor types are discussed. Such activation of the first 3 type of receptors causes a decrease in body temperature, whereas the 5-HT2 activation causes its increase. Physiological mechanisms leading to changes in body temperature as a result of 5-HT receptors' activation are discussed. In case of 5-HT1A receptor, they include an inhibition of shivering and non-shivering thermogenesis, as well simultaneous increase of peripheral blood flow, i.e., the processes of heat production and heat loss. The physiological processes mediated by 5-HT2 receptor are opposite to those of the 5-HT1A receptor. Mechanisms of 5-HT3 and 5-HT7 receptor participation in these processes are yet to be studied in more detail. Some facts indicating that in natural conditions, without pharmacological impact, these 5-HT receptors are important links in the system of temperature homeostasis, are also discussed.

Control of Shivering During Targeted Temperature Management

Targeted temperature management (TTM) is used frequently in patients with a variety of diseases, especially those who have experienced brain injury and/or cardiac arrest. Shivering is one of the main adverse effects of TTM that can often limit its implementation and efficacy. Shivering is the body's natural response to hypothermia and its deleterious effects can negate the benefits of TTM. The purpose of this article is to provide an overview of TTM strategies and shivering management.

Possible Biological Mechanisms Linking Mental Health and Heat-A Contemplative Review

This review provides examples of possible biological mechanisms that could, at least partly, explain the existing epidemiological evidence of heatwave-related exacerbation of mental disease morbidity. The author reviews the complicated central processes involved in the challenge of maintaining a stable body temperature in hot environments, and the maladaptive effects of certain psychiatric medicines on thermoregulation. In addition, the author discusses some alternative mechanisms, such as interrupted functional brain connectivity and the effect of disrupted sleep, which may further increase the vulnerability of mental health patients during heatwaves.

Moderate intensity, exercise-induced catecholamine release in the preoptic area and anterior hypothalamus in rats is enhanced in a warm environment

Thermoeffector responses and core body temperature (T_core) homeostasis during exercise are affected by both ambient temperature and exercise intensity. We have previously reported that T_core, heat loss responses, and catecholamine release in the preoptic area and anterior hypothalamus (PO/AH) increased during incremental treadmill running. However, no previous study has examined whether changes in the thermoregulatory responses at warm ambient temperature are related to catecholamine responses during moderate intensity exercise in rats. Therefore, the aim of the present study was to investigate the responsiveness of neurotransmission in the PO/AH to moderate intensity exercise at different ambient temperatures, and to relate this to changes in thermoregulation. We measured the monoamine levels in the PO/AH and the thermoregulatory responses in exercising rats simultaneously using a combination of methods, including in vivo microdialysis, biotelemetry, and animal O²/CO² metabolism measuring system. On the day of experiments, rats ran for 60min at a speed of 18mmin^-1 on a treadmill at a 5% gradient, in an ambient temperature of 23°C or 30°C. T_core, tail skin temperature (T_tail; an index of heat loss), and oxygen consumption (V̇O₂: an index of heat production) were monitored. Dopamine (DA), noradrenaline (NA), and serotonin (5-HT) levels were measured by high performance liquid chromatography (HPLC) with electrochemical detection. Exercise significantly increased the T_core, T_tail, and V̇O₂ values, as well as DA and NA release in the PO/AH at both temperatures, and the increases were more pronounced at the warm ambient temperature. The results suggest that the increase in the T_core, heat production, and heat loss responses even during moderate intensity running in a warm environment are likely associated with an increase in DA and NA release in the PO/AH region.

Involvement of serotonin in the ventral tegmental area in thermoregulation of freely moving rats

We have recently reported that the serotonin (5-HT) projections from the midbrain's raphe nuclei that contains 5-HT cell bodies may play a role both in heat production and in heat loss. The purpose of the present study was to clarify the involvement of 5-HT in the ventral tegmental area (VTA), where 5-HT is suggested to participate in thermoregulation, using the combined methods of telemetry, microdialysis, and high performance liquid chromatography, with a special emphasis on regulation of the body temperature (T_b) in freely moving rats. First, we measured changes in T_b, tail skin temperature (T_tail; an index of heat loss), heart rate (HR; an index of heat production), locomotor activity (Act), and levels of extracellular monoamines in the VTA during cold (5°C) or heat (35°C) exposure. Subsequently, we perfused citalopram (5-HT re-uptake inhibitor) into the VTA and measured the thermoregulatory parameters and monoamines release. Although T_b, T_tail, and HR changed during both exposures, significant changes in extracellular level of 5-HT (138.7±12.7% baseline, p<0.01), but not dopamine (DA) or noradrenaline (NA) were noted in the VTA only during heat exposure. In addition, perfusion of citalopram into the VTA increased extracellular 5-HT levels (221.0±52.2% baseline, p<0.01), but not DA or NA, while T_b decreased from 37.4±0.1°C to 36.8±0.2°C (p<0.001),T_tail increased from 26.3±0.4°C to 28.4±0.4°C (p<0.001), and HR and Act remained unchanged. Our results suggest that the VTA is a key area for thermoregulation, and 5-HT, but not DA or NA, modulates the heat loss system through action in the VTA.

Analytic Review: Disorders of Temperature Control: Part I. Hyperthermia

After a review of the normal physiology of temperature regulation, one of the three hyperthermic syndromes— heat stroke—is discussed in detail with respect to its pathogenesis, pathophysiology, diagnosis, differential diagnosis, and treatment. The other syndromes— malignant hyperthermia and neuroleptic malignant syndrome—are discussed in Part II. Heat stroke is a syndrome of acute thermoregulatory failure in warm environments; malignant hyperthermia is a drug or stress-induced hypermetabolic syndrome characterized by vigorous muscular contractions; and the neuroleptic malignant syndrome results primarily from an imbalance of central neurotransmitters, usually due to neuroleptic drug use and characterized by muscular rigidity. Knowledge of the normal physiology of temperature regulation and the causes and pathophysiology of heat stroke are keys to understanding the other two syndromes.

Transcriptome composition of the preoptic area in mid-age and escitalopram treatment in male mice

The decrease in serotonergic neurotransmission during aging can increase the risk of neuropsychiatric diseases such as depression in elderly population and decline the reproductive system. Therefore, it is important to understand the age-associated molecular mechanisms of brain aging. In this study, the effect of aging and chronic escitalopram (antidepressant) treatment to admit mice was investigated by comparing transcriptomes in the preoptic area (POA) which is a key nucleus for reproduction. In the mid-aged brain, the immune system-related genes were increased and hormone response-related genes were decreased. In the escitalopram treated brains, transcription-, granule cell proliferation- and vasoconstriction-related genes were increased and olfactory receptors were decreased. Since homeostasis and neuroprotection-related genes were altered in both of mid-age and escitalopram treatment, these genes could be important for serotonin related physiologies in the POA.

5-HT2 receptor affinity, docking studies and pharmacological evaluation of a series of 1,3-disubstituted thiourea derivatives

A series of 10 thiourea derivatives have been synthesized by the reaction of aromatic amine with a substituted aryl (compounds 1-3, 6-8) and alkylphenyl (4, 5, 9, 10) isothiocyanates. Their in vitro and in vivo pharmacological properties were studied. Among the evaluated compounds, two displayed very high affinity for the 5-HT2A receptor (1-0.043 nM and 5-0.6 nM), being selective over the 5-HT2C receptor. Derivatives 3, 5, 9, 10 by 70-89% diminished L-5-HTP-induced head twitch episodes. Compounds 1 and 5 as the 5-HT2A receptor antagonists produced a dose-dependent decrease in the number of DOI-elicited HTR. Compounds 1-5 strongly reduced amphetamine-evoked hyperactivity in rodents. In another test, 1 and 2 caused hyperthermia in mice, whereas 9 and 10 led to hypothermia. Antinociceptive and anticonvulsant properties of selected derivatives were demonstrated. Molecular docking studies using a homology model of 5-HT2A revealed a significant role of hydrogen bonds between both thiourea NH groups and Asp155/Tyr370 residues, as well as π-π interaction with Phe339.

Synthesis, central nervous system activity and structure-activity relationships of novel 1-(1-Alkyl-4-aryl-4,5-dihydro-1H-imidazo)-3-substituted urea derivatives

A series of 10 novel urea derivatives has been synthesized and evaluated for their central nervous system activity. Compounds 3a-3h were prepared in the reaction between the respective 1-alkyl-4-aryl-4,5-dihydro-1H-imidazol-2-amines 1a and 1b and appropriate benzyl-, phenethyl-isocyanate or ethyl 4-isocyanatobenzoate and ethyl isocyanatoacetate 2 in dichloromethane. Derivatives 4c and 4g resulted from the conversion of 3c and 3g into the respective amides due to action of an aqueous ammonia solution. The results obtained in this study, based on literature data suggest a possible involvement of serotonin system and/or the opioid system in the effects of tested compounds, and especially in the effect of compound 3h. The best activity of compound 3h may be primarily attributed to its favourable ADMET properties, i.e., higher lipophilicity (related to lower polar surface area and greater molecular surface, volume and mass than for other compounds) and good blood-brain permeation. This compound has also the greatest polarizability and ovality. The HOMO and LUMO energies do not seem to be directly related to activity.

Neuronal serotonin release triggers the heat shock response in C. elegans in the absence of temperature increase

BACKGROUND

Cellular mechanisms aimed at repairing protein damage and maintaining homeostasis, widely understood to be triggered by the damage itself, have recently been shown to be under cell nonautonomous control in the metazoan C. elegans. The heat shock response (HSR) is one such conserved mechanism, activated by cells upon exposure to proteotoxic conditions such as heat. Previously, we had shown that this conserved cytoprotective response is regulated by the thermosensory neuronal circuitry of C. elegans. Here, we investigate the mechanisms and physiological relevance of neuronal control.

RESULTS

By combining optogenetic methods with live visualization of the dynamics of the heat shock transcription factor (HSF1), we show that excitation of the AFD thermosensory neurons is sufficient to activate HSF1 in another cell, even in the absence of temperature increase. Excitation of the AFD thermosensory neurons enhances serotonin release. Serotonin release elicited by direct optogenetic stimulation of serotonergic neurons activates HSF1 and upregulates molecular chaperones through the metabotropic serotonin receptor SER-1. Consequently, excitation of serotonergic neurons alone can suppress protein misfolding in C. elegans peripheral tissue.

CONCLUSIONS

These studies imply that thermosensory activity coupled to serotonergic signaling is sufficient to activate the protective HSR prior to frank proteotoxic damage. The ability of neurosensory release of serotonin to control cellular stress responses and activate HSF1 has powerful implications for the treatment of protein conformation diseases.

Efficacy and safety of ondansetron in preventing postanesthesia shivering: a meta-analysis of randomized controlled trials

BACKGROUND

Shivering is a very common complication in the postanesthesia period. Increasing studies have reported ondansetron may be effective in prevention of postanesthesia shivering (PAS). However, the results remained controversial; hence we conducted a meta-analysis of randomized controlled trials to evaluate the efficacy and safety of ondansetron on the prevention of postanesthesia shivering.

METHODS

PubMed and Embase databases were searched to identify the eligible randomized controlled trials assessing the effect of ondansetron on the prevention of PAS. Results were expressed as risk ratios (RRs) with accompanying 95% confidence intervals (CIs). The meta-analysis was performed with fixed-effect model or random-effect model according to the heterogeneity.

RESULTS

Six trials including 533 subjects were included. Compared with placebo, ondansetron was associated with a significant reduction of PAS (RR 0.43, 95% CI, 0.27-0.70), without an increased risk of bradycardia (RR 0.37, 95% CI, 0.12-1.15). Compared with meperidine, no difference was observed in the incidence of PAS (RR 0.68, 95% CI, 0.39-1.19) and bradycardia (RR 2.0, 95% CI, 0.38-10.64).

CONCLUSIONS

Ondansetron has a preventive effect on PAS without a paralleled side effect of bradycardia.

Pharmacologic options for reducing the shivering response to therapeutic hypothermia

Recent literature has demonstrated significant improvements in neurologic outcomes in patients who have received induced hypothermia in the setting of out-of-hospital cardiac arrest. Through multiple metabolic mechanisms, the induction of hypothermia slows the progression and devastation of transient cerebral hypoxia. Despite these benefits, the desired reduction in core temperature is often a challenging venture as the body attempts to maintain homeostasis through the induction of thermoregulatory processes aimed at elevating body temperature. Shivering is an involuntary muscular activity that enhances heat production in an attempt to restore homeostasis. For successful induction and maintenance of induced hypothermia, shivering, as well as other thermoregulatory responses, must be overcome. Several pharmacologic options are available, either used alone or in combination, that safely and effectively prevent or treat shivering after the induction of hypothermia. We conducted a PubMed search (1966-March 2009) to identify all human investigations published in English that discussed pharmacologic mechanisms for the control of shivering. Among these options, clonidine, dexmedetomidine, and meperidine have demonstrated the greatest and most clinically relevant impact on depression of the shivering threshold. More research in this area is needed, however, and the role of the clinical pharmacist in the development and implementation of this therapy needs to be defined.

Central fatigue and neurotransmitters, can thermoregulation be manipulated?

Fatigue is a complex phenomenon that can be evoked by peripheral and central factors. Although it is obvious that fatigue has peripheral causes such as glycogen depletion and cardiovascular strain, recent literature also focuses on the central origin of fatigue. It is clear that different brain neurotransmitters--such as serotonin, dopamine and noradrenaline--are implicated in the occurrence of fatigue, but manipulation of these neurotransmitters produced no conclusive results on performance in normal ambient temperature. Exercise in the heat not only adds an extra challenge to the cardiorespiratory system, but also to the brain. This provides a useful tool to investigate the association between exercise-induced hyperthermia and central fatigue. This review focuses on the effects of pharmacological manipulations on performance and thermoregulation in different ambient temperatures. Dopaminergic reuptake inhibition appears to counteract hyperthermia-induced fatigue in 30 °C, while noradrenergic neurotransmission shows negative effects on performance in both normal and high temperature, and serotonergic manipulations did not lead to significant changes in performance. It is, however, unlikely that one neurotransmitter system is responsible for the delay or onset of fatigue. Further research is required to determine the exact mechanisms of fatigue in different environmental conditions.

Alterations in central fatigue by pharmacological manipulations of neurotransmitters in normal and high ambient temperature

The scientific evidence is reviewed for the involvement of the brain monoamines serotonin, dopamine and noradrenaline (norepinephrine) in the onset of fatigue, in both normal and high ambient temperatures. The main focus is the pharmacological manipulations used to explore the central fatigue hypothesis. The original central fatigue hypothesis emphasizes that an exercise-induced increase in serotonin is responsible for the development of fatigue. However, several pharmacological studies attempted and failed to alter exercise capacity through changes in serotonergic neurotransmission in humans, indicating that the role of serotonin is often overrated. Recent studies, investigating the inhibition of the reuptake of both dopamine and noradrenaline, were capable of detecting changes in performance, specifically when ambient temperature was high. Dopamine and noradrenaline are prominent in innervated areas of the hypothalamus, therefore changes in the catecholaminergic concentrations may also be expected to be involved with the regulation of body core temperature during exercise in the heat. Evidence from different studies suggests that it is very unlikely that one neurotransmitter system is responsible for the appearance of central fatigue. The exact mechanism of fatigue is not known; presumably a complex interplay between both peripheral and central factors induces fatigue. Central fatigue will be determined by the collaboration of the different neurotransmitter systems, with the most important role possibly being for the catecholamines dopamine and noradrenaline.

Effect of chronic cold exposure on noradrenergic modulation in the preoptic area of thermoregulation in freely moving rats

For this study, we compared the thermoregulatory involvement of noradrenaline (NA) in the medial preoptic area (mPOA) of non-cold acclimated rats to that of cold-acclimated rats. We quantified the release of NA in the mPOA during 3 h cold (5 degrees C) exposure in room-temperature-acclimated rats (RA group, kept at 23 degrees C for 2 weeks) and cold-acclimated rats (CA group, kept at 5 degrees C for 2 weeks). We concurrently monitored the core body temperature (Tc), heart rate (HR), and tail skin temperature (Tt). Cold exposure significantly increased Tc and HR, and decreased Tt in both groups. However, the cold-induced increase of the extracellular NA levels in mPOA was observed only in the RA group: not in the CA group. To elucidate these different results in NA levels further, and to evaluate participation of the mPOA in thermoregulation in the cold, we measured Tc, HR, and Tt during perfusion of alpha-adrenoceptor antagonist phenoxybenzamine during cold exposure (5 degrees C). This pharmacological procedure induced marked hypothermia, with decreases in HR only in the RA group; no changes were observed in Tc or any thermoregulatory parameter in the CA group. These results suggest that NA in the mPOA modulates heat production in response to acute cold stress in the RA group. However, this thermoregulatory action of NA in the mPOA was attenuated in the CA group.

5-HT2A serotoninergic receptor in the locus coeruleus participates in the first phase of lipopolysaccharide-induced fever

This study was aimed at testing the hypothesis that serotoninergic receptors in the locus coeruleus (LC) play a role in bacterial lipopolysaccharide-induced fever. To this end, 5-HT1A (WAY-100635; 3 μg/100 nL) and 5-HT2A (ketanserin; 2 μg/100 nL) antagonists were microinjected into the LC and body temperature was monitored by biotelemetry. Intra-LC microinjections of ketanserin or WAY-100635 caused no change in body temperature of euthermic animals. 5-HT2A antagonism abolished the first phase of the lipopolysaccharide-induced fever. Taken together, these results indicate that serotonin acting on 5-HT2A receptors in the LC mediates the first phase of the febrile response, whereas 5-HT1A receptors are not involved in the lipopolysaccharide-induced fever.

Involvement of serotoninergic receptors in the anteroventral preoptic region on hypoxia-induced hypothermia

Hypoxia causes a regulated decrease in body temperature (Tb). There is circumstantial evidence that the neurotransmitter serotonin (5-HT) in the anteroventral preoptic region (AVPO) mediates this response. However, which 5-HT receptor(s) is (are) involved in this response has not been assessed. Thus, we investigated the participation of the 5-HT receptors (5-HT1, 5-HT2, and 5-HT7) in the AVPO in hypoxic hypothermia. To this end, Tb of conscious Wistar rats was monitored by biotelemetry before and after intra-AVPO microinjection of methysergide (a 5-HT1 and 5-HT2 receptor antagonist, 0.2 and 2 microg/100 nL), WAY-100635 (a 5-HT(1A) receptor antagonist, 0.3 and 3 microg/100 nL), and SB-269970 (a 5-HT7 receptor antagonist, 0.4 and 4 micro/100 nL), followed by 60 min of hypoxia exposure (7% O2). During the experiments, the mean chamber temperature was 24.6 +/- 0.7 degrees C (mean +/- SE) and the mean room temperature was 23.5 +/- 0.8 degrees C (mean +/- SE). Intra-AVPO microinjection of vehicle or 5-HT antagonists did not change Tb during normoxic conditions. Exposure of rats to 7% of inspired oxygen evoked typical hypoxia-induced hypothermia after vehicle microinjection, which was not affected by both doses of methysergide. However, WAY-100635 and SB-269970 treatment attenuated the drop in Tb in response to hypoxia. The effect was more pronounced with the 5-HT7 antagonist since both doses (0.4 and 4 microg/0.1 microL) were capable of attenuating the hypothermic response. As to the 5-HT(1A) antagonist, the attenuation of hypoxia-induced hypothermia was only observed at the higher dose. Therefore, the present results are consistent with the notion that 5-HT acts on both 5-HT(1A) and 5-HT7 receptors in the AVPO to induce hypothermia, during hypoxia.

Changes of body temperature and extracellular serotonin level in the preoptic area and anterior hypothalamus after thermal or serotonergic pharmacological stimulation of freely moving rats

Although many studies has been shown that serotonin (5-HT) in the preoptic area and anterior hypothalamus (PO/AH) is important for regulating body temperature (Tb), the exact role is not established yet due to conflicting results probably related to experimental techniques or conditions such as the use of anesthesia. The purpose of present study was to clarify the role of 5-HT in the PO/AH using the combined methods of telemetry, microdialysis and high performance liquid chromatography (HPLC), with a special emphasis on the regulation of Tb in freely moving rats. Firstly, we measured changes in Tb and levels of extracellular 5-HT and its metabolite 5-hydroxyindoleacetic acid (5-HIAA) in the PO/AH during cold (5 degrees C) and heat (35 degrees C) exposure. We also perfused fluoxetine (5-HT re-uptake inhibitor) and 8-hydroxy-2-(Di-n-propylamino)tetralin (8-OH-DPAT: 5-HT1A agonist) into the PO/AH. During both exposures, although Tb changed significantly, no significant changes were noted in extracellular levels of 5-HT and 5-HIAA in the PO/AH. In addition, although perfusion of fluoxetine or 8-OH-DPAT into the PO/AH increased or decreased extracellular 5-HT and 5-HIAA levels in the PO/AH respectively, but Tb did not change at all. Our results suggest that 5-HT in the PO/AH may not mediate acute changes in thermoregulation.

Some historical perspectives on thermoregulation

In this paper, selected historical aspects of thermoregulation and fever are presented as background to the application of molecular biology to thermoregulation. Temperature-sensing mechanisms, coordination of thermal information, thermoregulatory circuitry, efferent responses to thermal stimuli, set point mechanisms, and some of the mechanisms and consequences of fever and hyperthermia are highlighted. Neurotransmitters used in thermoregulatory circuits are also discussed. An attempt is made to include information from comparative physiological sources. Possible future avenues of research in the light of recent new technologies are also presented.

Hyperthermia: is it an ominous sign after cardiac arrest?

OBJECTIVE

To clarify the clinical characteristics of hyperthermia at an early stage after resuscitation from cardiac arrest (CA).

MATERIALS AND METHODS

We reviewed the medical records of 43 adult patients with non-traumatic out-of-hospital CA, who survived for longer than 24 h after admission to our intensive care unit (ICU) between January, 1995, and December, 1998. The patients were divided into two groups: a clinical brain death (CBD) group (n=23) and a non-CBD group (n=20), and various factors relating to hyperthermia were compared between the two groups.

RESULTS

The mean value of peak axillary temperatures within 72 h of admission was 39.8+/-0.9 degrees C for the CBD group, which was significantly greater than 38.3+/-0.6 degrees C for the non-CBD group (P<0.0001). The time of occurrence of the peak axillary temperature was at 19+/-16 h of admission in the CBD group and 20+/-18 h in the non-CBD group (not significantly different). There were no significant differences in risk factors relating to the occurrence of hyperthermia between the two groups, except for the number of patients who received epinephrine at ICU. In 23 patients with a peak axillary temperature of > or =39 degrees C during the first 72 h of hospitalization, brain death was diagnosed in 20 patients, whereas only 3 of 20 patients having a peak axillary temperature of <39 degrees C developed brain death (odds ratio, 37.8; 95% confidence interval, 6.72-212.2).

CONCLUSION

Hyperthermia at an early stage after resuscitation from CA may be associated with the outcome of brain death.

Biogenic amines and thermoregulatory changes

This review recapitulates the general principles of the organization of the thermoregulatory system, describes the thermoregulatory reactions of small and large mammals to hot environment and analyzes the probable roles of biogenic amines in these responses. Catecholamines found in peripheral blood plasma or excreted in urine represent a spillover of mediators released partly from sympathetic nerve endings and partly from the adrenal medulla. Since the thermoregulatory efforts differ between small and large mammals in cold and hot environments, the peripheral release of catecholamines is also different in these animals. The levels of these signal substances in the blood, as well as their peripheral metabolic and functional effects, serve as feedback signals for the hypothalamic integrative circuitry. The roles of antagonistic modulatory monoaminergic systems, ascending from the lower brain stem to the hypothalamus, in these integrations were discussed only partly, because this was a topic of another recent review (Zeisberger and Roth, 1996).

Anthropometric status and resting metabolic rate in users of the areca nut and smokers of tobacco in rural Sarawak

The areca nut is chewed by many of the world's population, mainly in South and Southeast Asia. Anthropometric data for 458 Sarawaki adults aged over 24 years, measured both in 1990 and in 1996, were examined in relation to use of tobacco and areca nut. Compared to non-smokers, smoking men were significantly taller and slightly (not significantly) thinner in both years, while smoking women were thinner in 1990 and slightly (not significantly) thinner in 1996. In both sexes there was an increase in the mean and range of body mass index (BMI, W/H2) over the 6-year interval. Smoking women showed a significantly smaller increment in BMI after allowing for areca nut use, which was associated with a similar trend, and this finding depended on including areca use in the model. The trend for men was similar. Possible effects of areca use could reflect variation in 'affluence' or conservatism, or appetite suppression. However, resting metabolic rate in 54 men and 70 women aged 24-60 years was associated with areca use. This association appeared to be mediated by the maximum room temperature of the 24 h preceding measurement. In women, a significant curvilinear association of RMR with maximum temperature was found in users of areca nut but not in non-users. In men, RMR was 7% higher (p < 0.05) in users of areca nut than in non-users, after allowing for age, height, weight, the sum of four skinfold thicknesses, and haemoglobin, but the association with maximum temperature was similar in both groups. It is speculated that constituents of areca nut modulate thermoregulatory pathways, resulting in prolonged temperature-dependent and hyperthermic heat production in this population; that males are more responsive to this effect than females; and that by this mechanism, and possibly also through centrally mediated effects on appetite for food, areca use could contribute to long-term variation in energy balance represented by change in BMI.

Central serotonin level-dependent changes in body temperature following administration of tryptophan to pargyline- and harmaline-pretreated rats

1. The effect of tryptophan on body temperature was studied in rats pretreated with pargyline, an irreversible monoamine oxidase inhibitor (MAOI), and harmaline, a reversible MAOI. 2. Tryptophan (100 mg/kg IP) produced hypothermia followed by hyperthermia in pargyline-pretreated rats, and hypothermia in harmaline-pretreated rats, but tryptophan did not cause body temperature changes by itself. 3. The tryptophan-induced hypo- and hyperthermic effects, which peaked at about 1 and 6 hr after tryptophan administration, respectively, were accompanied by a significant increase in serotonin (5-HT) levels in the pargyline-pretreated rat brain (75%-138.7% and 207%-240.9% increase, respectively), and the 5-HT levels in the hyperthermic state were significantly higher than those in the hypothermic state. 4. In harmaline-pretreated rats, tryptophan also increased the central 5-HT levels (80.5%-95.5% increase) in the hypothermic state, and the effect peaked at about 1 hr after tryptophan administration. The central 5-HT levels in harmaline-pretreated rats slightly decreased at 6 hr after tryptophan administration and were significantly lower than those in the hyperthermic state in the pargyline-pretreated rats. 5. Tryptophan (100 mg/kg IP) administration decreased 5-hydroxy indole acetic acid (5-HIAA) levels, 5-HT turnover, and dopamine (DA) turnover in the brain of pargyline-pretreated rats, but these parameters were not significantly different between the hypothermic and hyperthermic states (i.e., at 1 and 6 hr after tryptophan administration, respectively). 6. These results suggest that the tryptophan-induced body temperature change depends on the different 5-HT levels in the brain and that the 5-HT level needed to induce hyperthermia is higher than that needed to induce hypothermia.

5-HT1A and 5-HT2 receptors mediate hypo- and hyperthermic effects of tryptophan in pargyline-pretreated rats

Mechanisms of tryptophan (a 5-HT precursor)-induced changes in body temperature were investigated in rats pretreated with pargyline, a monoamine oxidase inhibitor (MAO-I). Tryptophan (100 mg/kg, i.p.) did not affect the body temperature in rats, but it produced significant hypothermia followed by marked hyperthermia and higher mortality in the pargyline-pretreated rats. 5-HT depletion with p-chlorophenylalanine (p-CPA, 100 mg/kg/day for 3 days) significantly suppressed not only the body temperature change but also the mortality and 5-HT syndrome following tryptophan plus pargyline administration. Although propranolol (10 mg/kg, i.p.), a beta-adrenoceptor antagonist, did not alter the hypothermia caused by tryptophan in the pargyline-pretreated rats, pindolol (2 mg/kg, S.C.), a 5-HT1A receptor and beta-adrenoceptor antagonist, suppressed the hypothermia but not the hyperthermia or mortality caused by the same treatment. On the other hand, spiperone and ketanserin, 5-HT2 receptor antagonists, at doses of 3 mg/kg, potentiated the hypothermia and completely suppressed the hyperthermia and mortality caused by tryptophan in the pargyline-pretreated rats. These results suggest that tryptophan-induced hypo- and hyperthermia are mediated by 5-HT1A and 5-HT2 receptors, respectively, in the pargyline-pretreated pretreated rats.

Thermoregulatory responses following injection of 5-hydroxytryptamine into the septohippocampal complex in rats

The present study investigated the change in thermoregulatory responses following microinjection of 5-hydroxytryptamine (5-HT) into the lateral septum and the hippocampus of unanesthetized, unrestrained rats. Intraseptal injection of 5-HT (5 to 20 micrograms) caused a dose-related fall in core temperature (Tb), which was associated with a decrease in heat production (HP). As the decrease in HP can not completely account for the magnitude of the decrease in Tb, increase in heat loss may also be involved in the 5-HT-induced hypothermia. In contrast to observed changes following intraseptal injection, no significant change in either Tb or HP was observed after microinjection of the same doses of 5-HT into the hippocampal areas, indicating that the hypothermic response to intraseptal injection of 5-HT is site specific. Further, the hypothermic response to intraseptal injection of 5-HT was only attenuated by systemic pretreatment with cyproheptadine, but not by naloxone or scopolamine, indicating that the hypothermic response is mediated by 5-HT receptor, but not by endogenous opioid and cholinergic systems.

Effects of whole body microwave exposure on the rat brain contents of biogenic amines

The effects of whole body microwave exposure on the central nervous system (CNS) of the rat were investigated. Rats weighing from 250 to 320 g were exposed for 1 h to whole body microwave with a frequency of 2450 MHz at power densities of 5 and 10 mW.cm-2 at an ambient temperature of 21-23 degrees C. The rectal temperatures of the rats were measured just before and after microwave exposure and mono-amines and their metabolites in various discrete brain regions were determined after microwave exposure. Microwave exposure at power densities of 5 and 10 mW.cm-2 increased the mean rectal temperature by 2.3 degrees C and 3.4 degrees C, respectively. The noradrenaline content in the hypothalamus was significantly reduced after microwave exposure at a power density of 10 mW.cm-2. There were no differences in the dopamine (DA) content of any region of the brain between microwave exposed rats and control rats. The dihydroxyphenyl acetic acid (DOPAC) content, the main metabolite of DA, was significantly increased in the pons plus medulla oblongata only at a power density of 10 mW.cm-2. The DA turnover rates, the DOPAC:DA ratio, in the striatum and cerebral cortex were significantly increased only at a power density of 10 mW.cm-2. The serotonin (5-hydroxytryptamine, 5-HT) content in all regions of the brain of microwave exposed rats was not different from that of the control rats. The 5-hydroxyindoleacetic acid (5-HIAA) content in the cerebral cortex of microwave exposed rats was significantly increased at power densities of 5 and 10 mW.cm-2.(ABSTRACT TRUNCATED AT 250 WORDS)

Potentiating effect of morphine upon d-methamphetamine-induced hyperthermia in mice. Effects of naloxone and haloperidol

We have examined changes in rectal temperature of mice after subcutaneous administrations of d-methamphetamine alone or methamphetamine plus morphine. Methamphetamine 5 mg/kg produced slight hyperthermia, while simultaneous administration of morphine (25-100 mg/kg), which alone produces hypothermia, potentiated markedly the increase in body temperature by methamphetamine. Methamphetamine showed a hyperthermic effect in a dose-dependent manner in the presence of morphine. The hyperthermia due to methamphetamine plus morphine was avoided by pretreatment with 10 mg/kg naloxone. When animals were pretreated with 2.5 mg/kg haloperidol, hyperthermia due to methamphetamine alone was completely abolished, while that due to methamphetamine plus morphine was still observed. These results showed that dopamine may be implicated in methamphetamine hyperthermia and a haloperidol-nonsensitive mechanism may be involved in the methamphetamine-morphine hyperthermia.