EFFECTS ON TEMPERATURE OF AMINES INJECTED INTO THE CEREBRAL VENTRICLES. A NEW CONCEPT OF TEMPERATURE REGULATION

Dynamic Metabolic Response, Clotting Times and Peripheral Indices of Central Fatigue in Horse Competing in a 44 Km Endurance Race

A deep knowledge on metabolic response of athlete horse to exercise is of paramount importance for the development of optimal training programs to attain equilibrium between good performance and animal welfare. This study investigated the dynamic change of metabolic, clotting times and peripheral indices of central fatigue in horses competing in an official 44 km endurance race.  From 6 horses blood samples were collected at rest (T_PRE), within 5 minutes from the end of race (T_PE5), after 30, 60 minutes after the end of race (T_PE30 and T_PE60) to investigate the values of blood lactate, glucose, platelets (PLTs), serum leucine, isoleucine, valine, tryptophan, the ratio between tryptophan and branched-chain amino acids (BCAAs) levels (Try/BCAAs), total proteins, non-esterified fatty acids, plasma thrombin time (TT), prothrombin time (PT), activated partial thromboplastin time and fibrinogen (Fb). Lactate, PLTs, non-esterified fatty acids, BCAAs and Try/BCAAs showed higher values at T_PE5, T_PE30and T_PE60than T_PRE(P < .0001); glucose showed lower values at T_PE5, T_PE30and T_PE60than T_PRE(P < .0001). Higher TT values were found at T_PE5, T_PE30and T_PE60than T_PRE, and at T_PE5than T_PE30 and T_PE60(P < .0001); Fb was higher at T_PE5than T_PRE, T _PE30and T_PE60(P < .0001). This survey confirms that horses performing prolonged physical exercise experienced glycolysis, lipid mobilization and amino acid metabolism to provide substrates as fuel for muscle contraction.

Peripheral Modulators of the Central Fatigue Development and Their Relationship with Athletic Performance in Jumper Horses

The current study aimed to investigate whether peripheral modulators of serotoninergic function and neurohumoral factors' changes in athletic horses during an official jumping competition, and to evaluate their relationship with the physical performance of competing horses. From 7 Italian Saddle mares (6-9 years; mean body weight 440 ± 15 kg), performing the same standardized warm-up and jumping course during an official class, heart rate (HR) was monitored throughout the competition. Rectal temperature (RT) measurement, blood lactate and glucose concentration, serum tryptophan, leucine, valine, the tryptophan/branched-chain amino-acids ratio (Try/BCAAs), dopamine, prolactin, and non-esterified fatty acids (NEFAs) were assessed before the exercise event (T0), at the end of the competition stage (5 min ± 10 s following the cessation of the exercise, TPOST5), and 30 min after the end of competition (TPOST30). Highest HR values were recorded during the course and at the outbound (p < 0.0001); blood lactate concentration and RT increased after exercise with respect to the rest condition (p < 0.0001). Lower leucine and valine levels (p < 0.01), and higher tryptophan, Try/BCAAs ratio, and NEFAs values were found at TPOST5 and TPOST30 with respect to T0 (p < 0.0001). A higher prolactin concentration was found at TPOST5 and TPOST30 compared to T0 (p < 0.0001), whereas dopamine showed decreased values after exercise compared to rest (p < 0.0001). Statistically significant correlations among the peripheral indices of serotoninergic function, neurohumoral factors, and athletic performance parameters were found throughout the monitoring period. The findings provide indirect evidence that the serotoninergic system may be involved in fatigue during jumper exercise under a stressful situation, such as competition, in which, in addition to physical effort, athletic horses exhibit more passive behavior.

Therapeutic Hypothermia for Acute Stroke

Hypothermia is the most potent neuroprotective therapy available. Clinical use of hypothermia is limited by technology and homeostatic mechanisms that maintain core body temperature. Recent advances in intravascular cooling catheters and successful trials of hypothermia for cardiac arrest revivified interest in hypothermia for stroke, resulting in Phase 1 clinical trials and plans for further development. Given the recent spate of neuroprotective therapy failures, we sought to clarify whether clinical trials of therapeutic hypothermia should be mounted in stroke patients. We reviewed the preclinical and early clinical trials of hypothermia for a variety of indications, the putative mechanisms for neuroprotection with hypothermia, and offer several hypotheses that remain to be tested in clinical trials. Therapeutic hypothermia is promising, but further Phase 1 and Phase 2 development efforts are needed to ensure that cooling of stroke patients is safe, before definitive efficacy trials.

5-HT2A receptors control body temperature in mice during LPS-induced inflammation via regulation of NO production

G protein-coupled 5-HT2A receptors are involved in the regulation of numerous normal and pathological physiological functions. At the same time, its involvement in the regulation of body temperature (Tb) in normal conditions is obscure. Here we study the effect of the 5-HT2A receptor activation or blockade on Tb in sick animals. The experiments were carried out on adult C57BL/6 mouse males. Systemic inflammation and sickness were produced by lipopolysaccharide (LPS, 0.1mg/kg, ip), while the 5-HT2A receptor was stimulated or blocked through the administration of the receptor agonist DOI or antagonist ketanserin (1mg/kg), respectively. LPS, DOI or ketanserin alone produced no effect on Tb. However, administration of LPS together with a peripheral or central ketanserin injection reduced Tb (32.2°C). Ketanserin reversed the LPS-induced expression of inducible NO synthase in the brain. Consequently, an involvement of NO in the mechanism of the hypothermic effect of ketanserin in sick mice was hypothesized. Administration of LPS together with NO synthase inhibitor, l-nitro-arginine methyl ester (60mg/kg, ip) resulted in deep (28.5°C) and prolonged (8h) hypothermia, while administration of l-nitro-arginine methyl ester alone produced no effect on Tb. Thus, 5-HT2A receptors play a key role in Tb control in sick mice. Blockade of this GPCR produces hypothermia in mice with systemic inflammation via attenuation of LPS-induced NO production. These results indicate an unexpected role of 5-HT2A receptors in inflammation and NO production and have a considerable biological impact on understanding the mechanism of animal adaptation to pathogens and parasites. Moreover, adverse side effects of 5-HT2A receptor antagonists in patients with inflammation may be expected.

Normative database of the serotonergic system in healthy subjects using multi-tracer PET

The highly diverse serotonergic system with at least 16 different receptor subtypes is implicated in the pathophysiology of most neuropsychiatric disorders including affective and anxiety disorders, obsessive compulsive disorder, post-traumatic stress disorder, eating disorders, sleep disturbance, attention deficit/hyperactivity disorder, drug addiction, suicidal behavior, schizophrenia, Alzheimer, etc. Alterations of the interplay between various pre- and postsynaptic receptor subtypes might be involved in the pathogenesis of these disorders. However, there is a lack of comprehensive in vivo values using standardized procedures. In the current PET study we quantified 3 receptor subtypes, including the major inhibitory (5-HT(1A) and 5-HT(1B)) and excitatory (5-HT(2A)) receptors, and the transporter (5-HTT) in the brain of healthy human subjects to provide a database of standard values. PET scans were performed on 95 healthy subjects (age=28.0 ± 6.9 years; 59% males) using the selective radioligands [carbonyl-(11)C]WAY-100635, [(11)C]P943, [(18)F]altanserin and [(11)C]DASB, respectively. A standard template in MNI stereotactic space served for region of interest delineation. This template follows two anatomical parcellation schemes: 1) Brodmann areas including 41 regions and 2) AAL (automated anatomical labeling) including 52 regions. Standard values (mean, SD, and range) for each receptor and region are presented. Mean cortical and subcortical binding potential (BP) values were in good agreement with previously published human in vivo and post-mortem data. By means of linear equations, PET binding potentials were translated to post-mortem binding (provided in pmol/g), yielding 5.89 pmol/g (5-HT(1A)), 23.5 pmol/g (5-HT(1B)), 31.44 pmol/g (5-HT(2A)), and 11.33 pmol/g (5-HTT) being equivalent to the BP of 1, respectively. Furthermore, we computed individual voxel-wise maps with BP values and generated average tracer-specific whole-brain binding maps. This knowledge might improve our interpretation of the alterations taking place in the serotonergic system during neuropsychiatric disorders.

Central 5-HT3 receptor-induced hypothermia is associated with reduced metabolic rate and increased heat loss

Activation of central 5-HT(3) receptors by the selective agonist m-CPBG (1-(3-chlorophenyl)biguanide hydrochloride, 40 nM i.c.v.) produced stronger hypothermic effect in mice than activation of 5-HT(1A) receptors by their agonist 8-OH-DPAT (8-hydroxy-2-(di-n-propilamino)tetralin) injected by the same route at an equimolar dose. The hypothermic effect of m-CPBG was realized by influence on both the heat production and the heat loss: oxygen consumption and CO(2) expiration were decreased; heat dissipation determined by the tail skin temperature was increased. The heat loss effect of 5-HT(3) receptors was significantly shorter than the decrease in metabolism indicating the prevalent role of heat production decrease in 5-HT(3) receptor-induced deep and long-lasing hypothermia. In addition, the decrease in the respiratory exchange ratio (RER) was shown suggesting that the activation of the 5-HT(3) receptors switched metabolism to prevalent use of lipids as the main energetic substrate. 5-HT(1A) receptor agonist 8-OH-DPAT (40 nM i.c.v.) produced less depressing effect on general metabolism: a decrease in oxygen consumption and CO(2) excretion began later and was not so deep as after m-CPBG administration. Heat-loss effect of 5-HT(1A) receptors activation was not observed. In contrast to m-CPBG effect, RER after 5-HT(1A) receptors activation raised immediately after injection and then gradually decreased to the values observed in m-CPBG-treated mice. Obtained results show that activation of central 5-HT(3) receptors are more effective in hypothermia induction due to marked decrease in thermogenesis and increase in heat loss.

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.

An excitatory action of adrenaline, noradrenaline, and 5-hydroxytryptamine on the spinal cord

1. Fasciculation was produced in the trapezius and sternomastoid muscles of anaesthetized cats by adrenaline, noradrenaline and 5-hydroxytryptamine (5-HT) put into the cisterna magna. Isoprenaline, similarly applied, was ineffective.2. Each of the three active amines was without effect when applied for a second time after the fasciculation in response to the first application had passed off, but 5-HT was effective after adrenaline and, similarly, adrenaline after 5-HT.3. Fasciculation produced by adrenaline, but not by 5-HT, was inhibited by ergotamine or phenoxybenzamine, given intravenously.4. In producing fasciculation, the adrenaline appeared to be acting on or through the lateral aspect of the upper cervical cord, about the line of emergence of the roots of the spinal accessory nerve, mainly in C1 and C2.5. The electromyograms of the fasciculation due to adrenaline and 5-HT showed intermittent bursts of activity. After adrenaline, the bursts consisted of fewer spikes than after 5-HT. The intervals between consecutive spikes were 3.75-5 msec after either amine, and the bursts occurred irregularly, at frequencies between 7 and 12/sec.6. It is suggested that adrenaline and 5-HT have excitatory actions on the dendrites or somata of the spinal accessory motor neurones, and the possible role of these amines as synaptic transmitters in the spinal nucleus of the accessory nerve is discussed.

Gaddum and LSD: the birth and growth of experimental and clinical neuropharmacology research on 5-HT in the UK

The vasoconstrictor substance named serotonin was identified as 5-hydroxytryptamine (5-HT) by Maurice Rapport in 1949. In 1951, Rapport gave Gaddum samples of 5-HT substance allowing him to develop a bioassay to both detect and measure the amine. Gaddum and colleagues rapidly identified 5-HT in brain and showed that lysergic acid diethylamide (LSD) antagonized its action in peripheral tissues. Gaddum accordingly postulated that 5-HT might have a role in mood regulation. This review examines the role of UK scientists in the first 20 years following these major discoveries, discussing their role in developing assays for 5-HT in the CNS, identifying the enzymes involved in the synthesis and metabolism of 5-HT and investigating the effect of drugs on brain 5-HT. It reviews studies on the effects of LSD in humans, including Gaddum's self-administration experiments. It outlines investigations on the role of 5-HT in psychiatric disorders, including studies on the effect of antidepressant drugs on the 5-HT concentration in rodent and human brain, and the attempts to examine 5-HT biochemistry in the brains of patients with depressive illness. It is clear that a rather small group of both preclinical scientists and psychiatrists in the UK made major advances in our understanding of the role of 5-HT in the brain, paving the way for much of the knowledge now taken for granted when discussing ways that 5-HT might be involved in the control of mood and the idea that therapeutic drugs used to alleviate psychiatric illness might alter the function of cerebral 5-HT.

A theoretical consideration of the means whereby the mammalian core temperature is defended at a null zone

The neural process by which it is generally supposed that the stability of the body temperature of mammals is achieved has long been sought, but it remains unresolved. One hypothesis is that, as with many engineered physical systems, there is a stable reference signal with which a signal representative of body temperature is compared. Another hypothesis is that the differing coefficients of two signals that vary with temperature changes provide the set-level determinant. These could be the activities of the "cold" and "warm" sensors in response to temperature changes. Reciprocal crossing inhibition between the cold sensor to heat production effector pathways and the warm sensor to heat loss effector pathways through the central nervous system is a likely occurrence, and it could create the null-point temperature at which neither heat production nor heat loss effectors are active. This null point would be, seemingly, the set point at which body temperature is regulated. Neither hypothesis has been validated unequivocally. Students should be aware of this uncertainty about the physiological basis of homeothermy and, indeed, of homeostasis more generally. Perhaps we should be looking for a general principle that underlies the many physical and chemical stabilities of the internal environment, rather than considering them as quite separate accomplishments.

Characterisation of the selective 5-HT1B receptor antagonist SB-616234-A (1-[6-(cis-3,5-dimethylpiperazin-1-yl)-2,3-dihydro-5-methoxyindol-1-yl]-1-[2′-methyl-4′-(5-methyl-1,2,4-oxadiazol-3-yl)biphenyl-4-yl]methanone hydrochloride): In vivo neurochemical and behavioural evidence of anxiolytic/antidepressant activity

The 5-HT1B receptor has attracted significant interest as a potential target for the development of therapeutics for the treatment of affective disorders such as anxiety and depression. Here we present the in vivo characterisation of a novel, selective and orally bioavailable 5-HT1B receptor antagonist, SB-616234-A (1-[6-(cis-3,5-dimethylpiperazin-1-yl)-2,3-dihydro-5-methoxyindol-1-yl]-1-[2'-methyl-4'-(5-methyl-1,2,4-oxadiazol-3-yl)biphenyl-4-yl]methanone hydrochloride). SB-616234-A reversed the 5-HT1/7 receptor agonist, SKF-99101H-induced hypothermia in guinea pigs in a dose related manner with an ED50 of 2.4 mg/kg p.o. Using in vivo microdialysis in freely moving guinea pigs, SB-616234-A (3-30 mg/kg p.o.) caused a dose-related increase in extracellular 5-HT in the dentate gyrus. Evaluation of antidepressant- and anxiolytic-like effects of this 5-HT1B receptor antagonist was performed in a variety of models and species. SB-616234-A produced a decrease in immobility time in the mouse forced swim test; an effect suggestive of antidepressant activity. Furthermore, SB-616234-A produced dose-related anxiolytic effects in both rat and guinea pig maternal separation-induced vocalisation models with an ED50 of 1.0 and 3.3 mg/kg i.p., respectively (vs fluoxetine treatment ED50 = 2.2 mg/kg i.p. in both species). Also a significant reduction in posturing behaviours was observed in the human threat test in marmosets; an effect indicative of anxiolytic activity. In summary, SB-616234-A is a novel, potent and orally bioavailable 5-HT1B receptor antagonist which exhibits a neurochemical and behavioural profile that is consistent with both anxiolytic- and antidepressant-like activity in a variety of species. Taken together these data suggest that SB-616234-A may have therapeutic efficacy in the treatment of affective disorders.

Modulation of delta opioid-evoked hypothermia in rats by WAY 100635 and fluoxetine

Delta opioid receptor and 5-hydroxytryptamine (5-HT) interactions in rats were investigated using the endpoint of hypothermia. The intraperitoneal (i.p.) administration of SNC-80, a delta opioid agonist (35 mg/kg, i.p.), produced a significant hypothermia. For combined administration, SNC-80-evoked hypothermia was (1) abolished by pre-treatment with naltrindole (5 mg/kg, i.p.); (2) attenuated by pre-treatment with WAY 100635 (1 mg/kg, s.c.), a 5-HT1A antagonist; and (3) enhanced by pre-treatment with non-hypothermic doses of fluoxetine (2.5, 5 and 10 mg/kg, i.p.). The present data reveal that 5-HT1A receptor activation mediates a significant proportion of the hypothermic response to delta opioid receptor activation and that a 5-HT uptake blockade potentiates delta receptor-induced hypothermia.

Exercise thermoregulation and hyperprolactinaemia

The anterior pituitary hormone prolactin (PRL), measured in the peripheral blood circulation, reflects alterations in central brain 5-hydroxytryptamine (serotonin) and dopaminergic activity and is used as a marker of 'central fatigue' during active heat exposure. Significant correlations have consistently been found between PRL and core temperature (T(CORE)) during prolonged exercise. There has been no investigation into the relationship between PRL and other key thermoregulatory variables during exercise, such as weighted mean skin (T(SK)) and mean body temperature (T(B)), heat storage (HS), thermal gradient (T(GRAD)), heart rate (HR) and skin blood flow (cutaneous vascular conductance, CVC). Therefore, the aim of this study was to ascertain if a significant relationship exists between PRL and these thermoregulatory variables during prolonged exercise. Nine active male subjects conducted three trials of approximately 60% VO(2peak) at 70-80 rpm for 45 min on a semi-recumbent cycle ergometer at three different ambient temperatures [6 degrees C (Cold), 18 degrees C (Neutral) and 30 degrees C (Hot)] to elicit varying levels of thermoregulatory stress during exercise. Significant differences existed in T(SK), T(B), HS, T(GRAD) and CVC across the environmental conditions (p < 0.001). Core temperature (T(CORE)), HR and PRL were significantly elevated only in Hot (p < 0.05). Moderate correlations were found for T(CORE), T(SK), T(B), HS, T(GRAD), HR and CVC with post-exercise PRL (rho = 0.358-0.749). The end-of-exercise <38.0 degrees C T(CORE) responses were not (rho = -0.129, p > 0.05) but the >38.0 degrees C T(CORE) responses were (rho = 0.845, p < 0.001) significantly related to their corresponding PRL responses. The significant relationships between PRL release and T(SK), T(B), HS, T(GRAD), HR and CVC have extended previous research on T(CORE) and PRL release and indicate an association between these thermoregulatory variables, as well as T(CORE), and serotonergic/dopaminergic activity during prolonged exercise.

Paroxetine administration failed [corrected] to influence human exercise capacity, perceived effort or hormone responses during prolonged exercise in a warm environment

The purpose of the experiment was to examine whether selective serotonin (5-HT) re-uptake transporter blockade by paroxetine has any effect on perceived effort (RPE) during exercise or the time to reach volitional fatigue and on the prolactin and cortisol responses during prolonged exercise performed in a warm environment. Eight healthy males performed two cycle rides to exhaustion in a warm (32 degrees C) environment at 60% of maximum oxygen uptake. Paroxetine (20 mg) or placebo was administered 5 h before exercise trials in a randomised double blind fashion. Time to exhaustion was not significantly influenced by administration of paroxetine: median (range) time to exhaustion was 93.3 (76.2-175.0) min on the placebo trial and 92.5 (66.0-151.0) min on the paroxetine trial. Rectal temperature was higher at rest and throughout exercise on the paroxetine trial. The serum concentrations of prolactin and cortisol were determined throughout exercise as peripheral markers of central 5-HT activity. RPE increased over time but was not influenced by paroxetine administration. Prolactin and cortisol levels increased over time but paroxetine administration did not influence the hormone responses during exercise. In conclusion, acute administration of paroxetine failed to alter RPE, exercise capacity or the response of the determined peripheral hormone markers of central 5-HT activity during prolonged exercise in a warm environment.

Intracerebroventricular tryptophan increases heating and heat storage rate in exercising rats

The role of increased hypothalamic tryptophan (TRP) availability on thermoregulation and rates of core temperature increase and heat storage (HS) during exercise was studied in normal untrained rats running until fatigue. The rats were each anesthetized with 2.5% tribromoethanol (1.0 ml kg(-1) ip) and fitted with a chronic guiding cannula attached to the right lateral cerebral ventricle 1 week prior to the experiments. Immediately before exercise, they were randomly injected through these cannulae with 2.0 microl of 0.15 M NaCl (SAL; n=6) or 20.3 microM L-TRP solution (n=7). Exercise consisted of running on a treadmill at 18 m min(-1) and 5% inclination until fatigue. Body temperature was recorded before and during exercise with a thermistor probe implanted into the peritoneal area. Rates of core temperature increase (HR, degrees C min(-1)) and heat storage (HSR, cal min(-1)) were calculated. TRP-treated rats showed a rapid increase in body temperature which was faster than that observed in the saline-treated group during the exercise period. The TRP group also showed a higher rate of core temperature increase and HS. TRP-treated rats that presented higher HR and HSR also fatigued much earlier than saline-treated animals (16.8+/-1.1 min TRP vs. 40+/-3 min SAL). This suggests that the reduced running performance observed in TRP-treated rats is related to increased HR and HSR induced by intracerebroventricular injection of TRP in these animals.

Differences in hypothalamic Fos expressions between two heat stress conditions in conscious mice

Hyperthermia and dehydration were important physiological phenomena in heat stress. But, the degrees of these phenomena were changed by heat stress conditions, and the distinction between both phenomena is necessary for investigation of response for individual phenomenon. Heat stress at 34 degrees C for 60 min increased rectal temperature, and heat stress at 38.5 degrees C for 60 min further increased rectal temperature and increased osmolality in mice. We investigated the activated region in hypothalamus, which played a role in thermoregulation, fluid regulation and so on, using immunostaining for Fos protein under these conditions in conscious mice. At 34 degrees C, Fos-positive neurons increased in the median preoptic nucleus, lateral preoptic area and anterior hypothalamic area, which were known to be the thermoregulatory center, and the dorsomedial hypothalamic nucleus, which was known to control eating. At 38.5 degrees C, Fos-positive neurons further increased in the regions mentioned above and appeared in the lateral septal nucleus, medial preoptic area, lateral hypothalamic area and zona incerta, which were thought to be involved in thermoregulation and/or fluid regulation, and the paraventricular hypothalamic nucleus, supraoptic nucleus and supraoptic nucleus in the retrochiasmatic part, which were known to be involved in neuroendocrine effector systems. These results support that the activated regions in hypothalamus differed with heat stress conditions, which induced only hyperthermia and both hyperthermia and dehydration.

Buspirone and meperidine synergistically reduce the shivering threshold

Mild hypothermia (i.e., 34 degrees C) may prove therapeutic for patients with stroke, but it usually provokes shivering. We tested the hypothesis that the combination of buspirone (a serotonin 1A partial agonist) and meperidine synergistically reduces the shivering threshold (triggering tympanic membrane temperature) to at least 34 degrees C while producing little sedation or respiratory depression. Eight volunteers each participated on four randomly-assigned days: 1) large-dose oral buspirone (60 mg); 2) large-dose IV meperidine (target plasma concentration of 0.8 microg/mL); 3) the combination of buspirone (30 mg) and meperidine (0.4 microg/mL); and 4) a control day without drugs. Core hypothermia was induced by infusion of lactated Ringer's solution at 4 degrees C. The control shivering threshold was 35.7 degrees C +/- 0.2 degrees C. The threshold was 35.0 degrees C +/- 0.8 degrees C during large-dose buspirone and 33.4 degrees C +/- 0.3 degrees C during large-dose meperidine. The threshold during the combination of the two drugs was 33.4 degrees C +/- 0.7 degrees C. There was minimal sedation on the buspirone and combination days and mild sedation on the large-dose meperidine day. End-tidal PCO2 increased approximately 10 mm Hg with meperidine alone. Buspirone alone slightly reduced the shivering threshold. The combination of small-dose buspirone and small-dose meperidine acted synergistically to reduce the shivering threshold while causing little sedation or respiratory toxicity.

IMPLICATIONS

Mild hypothermia may be an effective treatment for acute stroke, but it usually triggers shivering, which could be harmful. Our results indicate that the combination of small-dose buspirone and small-dose meperidine acts synergistically to reduce the shivering threshold while causing little sedation or respiratory toxicity. This combination may facilitate the induction of therapeutic hypothermia in stroke victims.

Involvement of somatodendritic 5-HT(1A) receptors in Delta(9)-tetrahydrocannabinol-induced hypothermia in the rat

Previously, it has been reported that modulating serotonergic neurones by use of selective serotonin reuptake inhibitors (SSRI) can alter the hypothermic response produced by Delta(9)-tetrahydrocannabinol (Delta(9)-THC). The aim of the present study was to investigate the effect that activation or antagonism of 5-hydroxytryptamine (5-HT(1A)) receptors has on Delta(9)-THC-induced hypothermia. Delta(9)-THC (0.5, 2 and 5 mg/kg iv) decreased body temperature in a dose-related manner. Whilst having no significant effect on body temperature when administered 40 min prior to vehicle injection, the 5-HT(1A) receptor antagonist N-[2-[4-(2-methoxyphenyl)-1-piperazinyl]ethyl]-N-(2-pyridinyl) cyclohexanecarboxamide trihydrochloride (WAY 100635; 1 mg/kg sc) significantly potentiated the hypothermia produced by 2 and 5 mg/kg Delta(9)-THC. In order to investigate whether this effect was due to antagonism at somatodendritic autoreceptors in midbrain raphe nuclei, WAY 100635 or the 5-HT(1A) agonist 8-hydroxy-(di-n-propylamino) tetralin (8-OH-DPAT) was microinjected into either the median raphe nuclei (MRN) or dorsal raphe nuclei (DRN) 40 min prior to Delta(9)-THC injection. Following microinjection into the DRN, neither WAY 100635 (0.5 nmol/0.5 microl/10 s) nor 8-OH-DPAT (15.2 nmol/0.5 microl/10 s) had any significant effect on Delta(9)-THC-induced hypothermia. However, WAY 100635 when microinjected into the MRN significantly potentiated Delta(9)-THC-induced hypothermia, and 8-OH-DPAT microinjected into the MRN significantly inhibited Delta(9)-THC-induced hypothermia. It is suggested from these studies that the potentiation of Delta(9)-THC-induced hypothermia by WAY 100635 when administered peripherally is mainly due to antagonism at somatodendritic 5-HT(1A) autoreceptors in the MRN.

The role of preoptic area and anterior hypothalamus and median raphe nucleus on thermoregulatory system in freely moving rats

To clarify the role of the preoptic area and anterior hypothalamus (PO/AH) on thermoregulatory system and the effects of serotonergic innervation from the median raphe nucleus (MRN) on body temperature (Tb), we perfused tetrodotoxin (TTX) solution into the PO/AH or MRN by using a microdialysis technique at different ambient temperatures (5, 23 and 35 degrees C) in freely moving rats. Tb was continuously monitored by using a telemetry system. In the MRN, perfusion of TTX solution induced significant hypothermia in the normal environment, a greater decrease in Tb during cold exposure and had no effect on Tb during heat exposure. In the PO/AH, perfusion of TTX solution induced significant hyperthermia in normal environment, a greater increase in Tb during heat exposure and had no effect on Tb during cold exposure. Our results indicate that the PO/AH regulates mainly heat loss or inhibits the loci regulating heat production. Furthermore, heat production appears to be regulated by other loci receiving serotonergic innervation from the MRN.

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.

Modulation of delta9-tetrahydrocannabinol-induced hypothermia by fluoxetine in the rat

1. It has been suggested that the dose of delta9-tetrahydrocannabinol (delta9-THC) that induces hypothermia in the rat increases the release of brain 5-hydroxytryptamine (5-HT). In light of this, we investigated the hypothermia produced by delta4-THC, and the effect the selective serotonin reuptake inhibitor fluoxetine has on this response. 2. A significant dose-dependent decrease in body temperature occurred after i.v. administration of 0.5 to 5 mg kg(-1) delta9-THC; maximum decreases being 0.8+/-0.2 degrees C to 2.9+/-0.3 degrees C. This hypothermic response was attenuated by the cannabinoid CB1 receptor antagonist SR 141716. 3. Fluoxetine (10 mg kg(-1) i.p.) alone caused a decrease in body temperature of 0.6+/-0.1 degrees C (n=32, P < 0.05) after 40 min. However, pretreatment with fluoxetine (10 mg kg(-1) i.p.) 40 min before delta9-THC significantly reduced the delta9-THC-induced hypothermia (n=7-8, P < 0.05). Contrary to this antagonist-like effect, fluoxetine administered 40 min after delta9-THC significantly potentiated the delta9-THC-induced hypothermia, producing a maximum decrease of 3.2+/-0.3 degrees C. 4. It is suggested that the effect of fluoxetine on the delta9-THC-induced hypothermic response is dependent on the time of its administration relative to that of delta9-THC. Pretreatment with fluoxetine increases extracellular 5-HT due to reuptake inhibition. Increased extracellular 5-HT can activate autoreceptors which may decrease serotonergic activity, thereby reducing the delta9-THC-induced hypothermia. Conversely, when fluoxetine is administered after delta9-THC, the reuptake block is thought to potentiate the already activated serotonergic system, hence potentiating the delta9-THC-induced hypothermia.

Chronopharmacological study of KE-SI-TO components in mice

Influence of dosing time on pharmacological effects and toxicity of KE-SI-TO (KST) components, as well as the role of each component in the circadian rhythms of KST, was investigated in ICR male mice under an LD (12:12) cycle. The mice given Cinnamomi Cortex (258 mg/kg, i.p.) or Paeoniae Radix (258 mg/kg, i.p.) showed a significant circadian rhythm in the time spent on the hot plate with the shortest latency at 0900 and the longest one at 0100 (p<0.01, respectively). The mice given Cinnamomi Cortex or Glycyrrhizae Radix (129 mg/kg, i.p.) showed a significant circadian rhythm with the lowest rectal temperature (RT) at 1700 and the highest one at 0500 (p<0.01, respectively). Cinnamomi Cortex (850 mg/kg, i.p.)- or Glycyrrhizae Radix (2500 mg/kg, i.p.)-induced toxicity showed a significant circadian rhythm with the highest mortality at 1700 and the lowest one at 0500 (p<0.05, respectively). The rhythmic patterns of the drug-induced analgesia, hypothermia and toxicity resembled the overall rhythms occurring after KST (1000 or 6000 mg/kg, i.p.) injection. These results suggest that the circadian rhythms in actions of Cinnamomi Cortex, Paeoniae Radix and Glycyrrhizae Radix are mainly responsible for the rhythm in the effects and toxicity of KST.

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.

Chronopharmacological study of KE-SI-TO in mice

Influence of dosing time on pharmacological effects and toxicity of KE-SI-TO (KST), analgesic and antipyretic drug, was investigated in ICR male mice under LD (12:12) cycle. Significant circadian rhythms were demonstrated for analgesic and hypothermal effects of KST (1 g/kg, i.p.) with higher values in the dark and lower ones in the light (p<0.01, respectively). The rhythmic patterns of KST-induced analgesia and hypothermia resembled overall the rhythms occuring in the nondrugged state. Injection of KST resulted in a parallel increasing in latency to hot plate and a parallel decreasing in rectal temperature. KST (6 g/kg, i.p.)-induced toxicity also showed a significant circadian rhythm with the highest mortality at 1700 and the lowest one at 0500 (p<0.05). The principles and concepts of biological rhythm should be included in the consideration of the actions of KST.

Circadian rhythm of fever induced by interferon-alpha in mice

The influence of dosing time on the fever induced by interferon-alpha (IFN-alpha) was investigated in ICR male mice under light-dark cycle. There was a significant circadian rhythm in rectal temperature, as an index of fever, at 1 hr after IFN-alpha (10 MIU/kg, i.v.) injection. The rhythmic pattern resembled overall the rhythm occurring in the nondrugged state. IFN-alpha increased rectal temperature during the light phase, but not during the dark phase. The fever induced by IFN-alpha was blocked by indomethacin (10 mg/kg, i.p.) pretreatment. There was no significant difference of plasma IFN-alpha concentrations at 0.167, 0.5 and 1 hr after IFN-alpha injection. Therefore the dosing time dependent difference of fever induced by IFN-alpha may be caused via that of PGE2 level elevated by IFN-alpha. The choice of the most appropriate time of day for drug administration may help to achieve rational chronotherapeutics of IFN-alpha.

Possible mechanisms of central nervous system fatigue during exercise

Fatigue of voluntary muscular effort is a complex phenomenon. To date, relatively little attention has been placed on the role of the central nervous system (CNS) in fatigue during exercise despite the fact that the unwillingness to generate and maintain adequate CNS drive to the working muscle is the most likely explanation of fatigue for most people during normal activities. Several biological mechanisms have been proposed to explain CNS fatigue. Hypotheses have been developed for several neurotransmitters including serotonin (5-HT; 5-hydroxytryptamine), dopamine, and acetylcholine. The most prominent one involves an increase in 5-HT activity in various brain regions. Good evidence suggests that increases and decreases in brain 5-HT activity during prolonged exercise hasten and delay fatigue, respectively, and nutritional manipulations designed to attenuate brain 5-HT synthesis during prolonged exercise improve endurance performance. Other neuromodulators that may influence fatigue during exercise include cytokines and ammonia. Increases in several cytokines have been associated with reduced exercise tolerance associated with acute viral or bacterial infection. Accumulation of ammonia in the blood and brain during exercise could also negatively effect the CNS function and fatigue. Clearly fatigue during prolonged exercise is influenced by multiple CNS and peripheral factors. Further elucidation of how CNS influences affect fatigue is relevant for achieving optimal muscular performance in athletics as well as everyday life.

Third W.D.M. Paton Memorial Lecture Burn Oxford for a start

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Chronopharmacological study of acetylsalicylic acid in mice

Influence of dosing time on pharmacological effects and toxicity of acetylsalicylic acid was investigated in ICR male mice under light-dark (12:12) cycle. Significant circadian rhythms (day-night rhythms) were demonstrated for hypothermal and analgesic effects at 1 h after an injection of acetylsalicylic acid (200 mg/kg, i.p.) (P < 0.01, respectively). The rhythmic patterns of acetylsalicylic acid induced analgesia and hypothermia resembled overall the rhythms occurring in the non-drugged state. Injection of acetylsalicylic acid resulted in a parallel increase in latency to hot plate and a parallel decrease in rectal temperature. The relationship between plasma salicylate concentrations and responses was not clear. There was also a significant circadian rhythm in acetylsalicylic acid (850 mg/kg, i.p.) induced toxicity with the highest mortality at 17:00 and the lowest one at 05:00 (P < 0.05). Dosing time dependent kinetics of salicylate seems to be related to the rhythm of toxicity of the drug. The time in circadian stage at which acetylsalicylic acid is administered is essentially important in the actions of acetylsalicylic acid.

GABAergic system inducing hyperthermia in the rat preoptic area: its independence of prostaglandin E2 system

Brain temperature of conscious freely moving rats was recorded during perfusion of the preoptic area (POA) with neuroactive compounds using the microdialysis technique. Unilateral perfusion of the POA with the sodium channel blocking agent, tetrodotoxin (1 microM), induced a pronounced hyperthermia. Of the neuroactive compounds examined, the greatest thermogenic response to local perfusion of the POA was elicited by the GABAergic agonist, muscimol. Muscimol (10, 20 and 100 microM) exhibited a dose-dependent and reversible hyperthermia. This hyperthermia was attenuated by co-perfusion with the GABAergic antagonist, bicuculline (10 microM). Muscimol-induced hyperthermia was independent of prostaglandin biosynthesis, and additive with prostaglandin E2 (10 microM)-induced hyperthermia. Prostaglandin E2-induced hyperthermia was not affected by co-perfusion with bicuculline. These data suggest the existence of two independent neurochemical systems for genesis of hyperthermia colocalized within the POA.

Stress-related behavior and central norepinephrine concentrations in the REM sleep-deprived rat

Rapid eye movement sleep deprivation (REMd) is a potent stressor in the rat. Behavioral abnormalities are among the earliest overt symptoms of REMd, the mechanisms for which remain largely unknown. The phenomena of hyperphagia and weight loss that are associated with REMd may contribute to its later morbidity; however, little is known about the onset of these phenomena or the neurotransmitter mechanisms that are involved. The aim of this study was to determine whether the earliest effects of REMd on consumatory behavior in the rat and its performance in the swimming cylinder of Porsolt are related to changes in norepinephrine (NE) concentrations in the cerebral cortex and selected areas of the hypothalamus. Sprague-Dawley rats were divided into three groups (n = 6): the REMd group resided in a water tank on 6.5-cm diameter pedestals for 96 h; the tank control (TC) group resided in the water tank on 15-cm pedestals for 96 h; the cage controls (CC) remained in their home cages for the duration of the study. In the first series of experiments, body weights and caloric intake were recorded daily, along with the performance of all animals in the swimming cylinder of Porsolt. In the second series of experiments, body weights and caloric intake were recorded, but the Porsolt test was not employed and the brains were dissected after 96 h for NE analysis by HPLC. It was observed that the REMd group had lower immobility times (p < 0.05) in the Porsolt test after only 24 h, compared to groups TC and CC.(ABSTRACT TRUNCATED AT 250 WORDS)

Prostaglandins and hypothalamic neurotransmitter receptors involved in hyperthermia: a critical evaluation

The role of a prostaglandin of the E series (PGE) in the hypothalamic mechanisms underlying a fever continues to be controversial. This paper reviews the historical literature and current findings on the central action of the PGEs on body temperature (Tb). New experiments were undertaken to examine the local effect of muscarinic, nicotinic, serotonergic, alpha-adrenergic, or beta-adrenergic receptor antagonists at hypothalamic sites where PGE1 caused a rise in Tb of the primate. Guide tubes for microinjection were implanted stereotaxically above sites in and around the anterior hypothalamic, preoptic area (AH/POA) of male Macaque monkeys. Following postoperative recovery, 30-100 ng of PGE1 was micro-injected unilaterally in a volume of 1.0-1.5 microliter at sites in the AH/POA to evoke a rise in Tb, and once identified, pretreated with a receptor antagonist. PGE1 hyperthermia was significantly reduced by microinjections of the muscarinic and nicotinic antagonists, atropine, or mecamylamine, at PGE1 reactive sites in the AH/POA. The serotonergic antagonist, methysergide, injected at PGE1 sensitive sites in the ventromedial hypothalamus also attenuated the rise in Tb. However, the 5-HT reuptake blocker, fluoxetine, and the beta-adrenergic receptor antagonist, propranolol, injected in the AH/POA failed to alter the PGE1 hyperthermia. In contrast, the alpha-adrenergic antagonist, phentolamine, potentiated the increase in Tb at all PGE1 reactive sites in the hypothalamus. An updated model is presented to explain how the concurrent actions of aminergic neurotransmitters acting on their respective receptors in the hypothalamus can interact with a PGE to elicit hyperthermia. Finally, an evaluation of the current literature including recent findings on macrophage inflammatory protein (MIP-1) supports the conclusion that a PGE in the brain is neither an obligatory nor essential factor for the expression of a pyrogen fever.

The treatment and management of neuroleptic malignant syndrome

1. The neuroleptic malignant syndrome was initially described as a disorder specifically related to neuroleptic usage with frequent fatal outcome. The observations of variant or mild cases of this syndrome as well as case reports on neuroleptic-malignant-like syndromes in the absence of neuroleptics raises the issue of the usefulness of this terminology and highlights the potential for inappropriate management of this "malignant" syndrome. It has been suggested that hypothalamic thermoregulatory responses may involve an interplay among noradrenergic, cholinergic and serotonergic pathways. Out treatment strategy is based on the pharmacology of neuroleptics and empirical data, verified in our own clinical practice and considers that it is often difficult to determine whether certain physiologic states are a consequence to or specific triggering factors. 2. If a patient's temperature is less than 101, we emphasize vigorous treatment with anticholinergic agents, while simultaneously assessing the psychiatric need for neuroleptics versus medical risks. Given that the severe rigidity of NMS represents severe extrapyramidal effects of dopamine blockade, there is no reason to withhold anticholinergics in the absence of higher temperatures. Neuroleptics can be stopped at the discretion of the clinician even during circumstances when there is fever below 101. 3. In cases of severe EPS with fever greater than or equal to 101, we recommend stopping neuroleptics, treating with anticholinergics and starting with dopamine agonists. In the event of a poor response to dopamine agonists, a brief trial of dantrolene and/or benzodiazepines is recommended. Dantrolene should not be introduced for prolonged periods, since abnormal liver function studies have been observed in approximately 1.8% of patients. 4. In cases of extreme hyperpyrexia (fever greater than 103), clinicians should consider transfer to an ICU or another medical support. Extreme temperatures have been associated with potentially irreversible cerebellar or other brain damage, if not aggressively treated. If neuroleptics are later indicated, a 2 week interval after resolution of symptoms should be maintained before reinstituting neuroleptics. 5. In patients with severe EPS without fever, we emphasize aggressive use of anticholinergic therapy, while simultaneously considering the psychiatric need for neuroleptics versus medical risks. In all cases where a patient's swallowing, respirations or physical mobility is severely compromised, we suggest stopping neuroleptics. Anticholinergic agents should be continued for 7 days after neuroleptics are stopped. If anticholinergic agents are unsuccessful after 2-3 dosages, dopamine agonists may be added, while simultaneously monitoring vital signs. It should be emphasized that severe EPS sometimes takes days to improve even after neuroleptic cessation and the addition of anticholinergics.(ABSTRACT TRUNCATED AT 400 WORDS)

Effects of p-chlorophenylalanine on thermoregulation and sleep in rats

Sleep/waking and body temperature (Tb) were recorded in male rats in a 12:12 light-dark photoperiod at one of 3 ambient temperatures (Ta's): 20, 30, or 32 degrees C. After adaptation to the sleep recording chamber for at least 48 h, the rats were injected with saline at the beginning of lights-on (day S1). Twenty-four hours later (day P1), they were injected with PCPA (300 mg/kg, i.p.) and recordings continued for 4 more days (P2-P5). At these Ta's, hypothalamic 5-HT was depleted by 66-75% 30 h post-PCPA. Changes in both amplitude and acrophase of Tb depended on Ta. Compared to S1, amplitude was reduced on P2-P4 at 20 degrees C and on P3-P4 at 30 degrees C. Acrophase was advanced on P1-P3 at Ta 20 degrees C only. Sleep variables were generally independent of Ta and largely unchanged in the dark. In the light, amounts of slow-wave sleep (SWS) were depressed on P2-P4, number of bouts decreased on P3-P5 and percent nocturnality decreased on P2-P5. Bout length was depressed on P2 and lengthened on P4-P5. Acrophase was delayed on P2-P4 at Ta 30 degrees C. Amounts of rapid-eye-movement sleep (REMS) were depressed on P1-P3. REMS bout length decreased on P1-P3. The decreases in number of REMS bouts seen on P1-P3 depended on Ta. Changes in percent nocturnality and acrophase of REMS were minor. Waking----SWS transitions decreased on P3-P5 while SWS----REMS transitions were reduced on P1-P2. These results suggest that PCPA affects circadian aspects of both Tb and sleep, that 5-HT is important in the initiation of SWS bouts, and finally that the mechanisms by which 5-HT depletion affects Tb, SWS and REMS are different.