Drugs and body temperature

Control of the Cutaneous Circulation by the Central Nervous System

The central nervous system (CNS), via its control of sympathetic outflow, regulates blood flow to the acral cutaneous beds (containing arteriovenous anastomoses) as part of the homeostatic thermoregulatory process, as part of the febrile response, and as part of cognitive-emotional processes associated with purposeful interactions with the external environment, including those initiated by salient or threatening events (we go pale with fright). Inputs to the CNS for the thermoregulatory process include cutaneous sensory neurons, and neurons in the preoptic area sensitive to the temperature of the blood in the internal carotid artery. Inputs for cognitive-emotional control from the exteroceptive sense organs (touch, vision, sound, smell, etc.) are integrated in forebrain centers including the amygdala. Psychoactive drugs have major effects on the acral cutaneous circulation. Interoceptors, chemoreceptors more than baroreceptors, also influence cutaneous sympathetic outflow. A major advance has been the discovery of a lower brainstem control center in the rostral medullary raphé, regulating outflow to both brown adipose tissue (BAT) and to the acral cutaneous beds. Neurons in the medullary raphé, via their descending axonal projections, increase the discharge of spinal sympathetic preganglionic neurons controlling the cutaneous vasculature, utilizing glutamate, and serotonin as neurotransmitters. Present evidence suggests that both thermoregulatory and cognitive-emotional control of the cutaneous beds from preoptic, hypothalamic, and forebrain centers is channeled via the medullary raphé. Future studies will no doubt further unravel the details of neurotransmitter pathways connecting these rostral control centers with the medullary raphé, and those operative within the raphé itself. © 2016 American Physiological Society. Compr Physiol 6:1161-1197, 2016.

Activation of slowly conducting medullary raphé-spinal neurons, including serotonergic neurons, increases cutaneous sympathetic vasomotor discharge in rabbit

Neurons in the rostral medullary raphé/parapyramidal region regulate cutaneous sympathetic nerve discharge. Using focal electrical stimulation at different dorsoventral raphé/parapyramidal sites in anesthetized rabbits, we have now demonstrated that increases in ear pinna cutaneous sympathetic nerve discharge can be elicited only from sites within 1 mm of the ventral surface of the medulla. By comparing the latency to sympathetic discharge following stimulation at the ventral raphé site with the corresponding latency following stimulation of the spinal cord [third thoracic (T3) dorsolateral funiculus] we determined that the axonal conduction velocity of raphé-spinal neurons exciting ear pinna sympathetic vasomotor nerves is 0.8 ± 0.1 m/s ( n = 6, range 0.6–1.1 m/s). Applications of the 5-hydroxytryptamine (HT)2A antagonist trans-4-((3 Z)3-[(2-dimethylaminoethyl)oxyimino]-3-(2-fluorophenyl)propen-1-yl)-phenol, hemifumarate (SR-46349B, 80 μg/kg in 0.8 ml) to the cerebrospinal fluid above thoracic spinal cord (T1-T7), but not the lumbar spinal cord (L2-L4), reduced raphé-evoked increases in ear pinna sympathetic vasomotor discharge from 43 ± 9 to 16 ± 6% ( P < 0.01, n = 8). Subsequent application of the excitatory amino acid (EAA) antagonist kynurenic acid (25 μmol in 0.5 ml) substantially reduced the remaining evoked discharge (22 ± 8 to 6 ± 6%, P < 0.05, n = 5). Our conduction velocity data demonstrate that only slowly conducting raphé-spinal axons, in the unmyelinated range, contribute to sympathetic cutaneous vasomotor discharge evoked by electrical stimulation of the medullary raphé/parapyramidal region. Our pharmacological data provide evidence that raphé-spinal neurons using 5-HT as a neurotransmitter contribute to excitation of sympathetic preganglionic neurons regulating cutaneous vasomotor discharge. Raphé-spinal neurons using an EAA, perhaps glutamate, make a substantial contribution to the ear sympathetic nerve discharge evoked by raphé stimulation.

Muscarinic supersensitivity and impaired receptor desensitization in G protein-coupled receptor kinase 5-deficient mice

G protein-coupled receptor kinase 5 (GRK5) is a member of a family of enzymes that phosphorylate activated G protein-coupled receptors (GPCR). To address the physiological importance of GRK5-mediated regulation of GPCRs, mice bearing targeted deletion of the GRK5 gene (GRK5-KO) were generated. GRK5-KO mice exhibited mild spontaneous hypothermia as well as pronounced behavioral supersensitivity upon challenge with the nonselective muscarinic agonist oxotremorine. Classical cholinergic responses such as hypothermia, hypoactivity, tremor, and salivation were enhanced in GRK5-KO animals. The antinociceptive effect of oxotremorine was also potentiated and prolonged. Muscarinic receptors in brains from GRK5-KO mice resisted oxotremorine-induced desensitization, as assessed by oxotremorine-stimulated [5S]GTPgammaS binding. These data demonstrate that elimination of GRK5 results in cholinergic supersensitivity and impaired muscarinic receptor desensitization and suggest that a deficit of GPCR desensitization may be an underlying cause of behavioral supersensitivity.

The characterization of oxotremorine-induced hypothermic response in the rat

Oxotremorine is a muscarinic receptor agonist that induces a variety of physiological and behavioural effects including hypothermia in mice. These effects are antagonized dose-dependently by classical anticholinergic compounds such as atropine. Although the oxotremorine-induced hypothermic response has been demonstrated in mice, few studies of the effects of this muscarinic agonist have been made in the rat. The following studies were made in male Sprague Dawley rats: 1. an investigation of the dose-response relationship between oxotremorine and hypothermia; 2. an examination of the effect of housing on the oxotremorine-induced hypothermic response, and 3, an investigation of the acute administration of various doses of atropine sulphate on the hypothermia caused by oxotremorine. The results indicate that the dose-response relationship between oxotremorine and the antagonism of hypothermia is similar in rat as it is in mice. The results also showed that this effect did not occur in group-housed animals.

Muscarinic receptors regulate striatal neuropeptide gene expression in normal and amphetamine-treated rats

This study investigated the effects of pharmacological blockade or stimulation of muscarinic receptors on constitutive and amphetamine-stimulated preprodynorphin, substance P and pre-proenkephalin gene expression in rat striatum. Acute administration of the non-selective muscarinic antagonist, scopolamine (2.5, 5 and 10 mg/kg, s.c.), caused a dose-dependent increase in preprodynorphin and substance P, but not preproenkephalin, messenger RNA expression in the dorsal and ventral striatum as revealed by quantitative in situ hybridization. In contrast, acute injection of the non-selective muscarinic receptor agonist, oxotremorine (0.125, 0.25 and 0.5 mg/kg, s.c.), caused a dose-dependent increase in basal levels of preproenkephalin messenger RNA in the dorsal striatum, without causing a significant effect on constitutive striatal preprodynorphin and substance P expression. Pretreatment with scopolamine (2.5 mg/kg, s.c.) significantly augmented striatal induction of preprodynorphin and substance P messenger RNA induced by acute injection of amphetamine (1.25 and 2.5 mg/kg, i.p.), whereas scopolamine blocked amphetamine-stimulated striatal preproenkephalin expression. Pretreatment with oxotremorine (0.25 mg/kg, s.c.) significantly attenuated amphetamine (1.25 and 2.5 mg/kg, i.p.)-stimulated striatal preprodynorphin and, to a lesser degree, substance P messenger RNA expression. Oxotremorine tended to increase amphetamine-stimulated preproenkephalin messenger RNA expression, but the effect did not reach statistical significance. In addition, scopolamine increased spontaneous, and enhanced amphetamine-stimulated, behavioral activity, whereas oxotremorine attenuated amphetamine-stimulated behaviors. These data support the concept that cholinergic transmission, via interaction with muscarinic receptors, inhibits basal and D1 receptor-stimulated striatonigral dynorphin/substance P gene expression and facilitates striatopallidal enkephalin gene expression.

Behavioral and adaptive status in an experimental model of Alzheimer's disease in rats

Ten days after bilateral electrolytic lesions of nucleus basalis magnocellularis (NBM) we tested behavioral (spontaneous motor activity, acquisition and performance of two-way active avoidance, fear-response in open field test, foot shock induced aggression, depression-response in learned helplessness test) and adaptive status (body temperature at standard, hot and cold environment as well as cold restraint-induced gastric lesions) in adult male Wistar rats. Compared to intact control and sham-operated rats, the bilateral NBM-lesioned rats showed the significant impairment of learning behavior and reduced fear, aggression and depression as well as altered body temperature at standard and stressed conditions. Namely, it was established that body temperature in NBM-lesioned rats was significantly lower at standard laboratory conditions, but in these rats body temperature significantly was raised after exposing to cold and hot environment. On the other hand, spontaneous motor activity and number and length of cold restraint-induced gastric lesions (erosions and petechiae) in NBM-lesioned rats were similarly to those in both controls. It could be concluded that NBM plays a significant role in cognitive, emotional and adaptive processes in the rats.

Higher environmental temperature-induced increase of body temperature: involvement of central opioidergic-GABAergic interaction

Exposure (2 h) of male albino rats to higher environmental temperature (HET, 40 degrees C) significantly increased the body temperature (BT). Administration of bicuculline (1 mg/kg, i.p.), physostigmine (0.2 mg/kg, i.p.), or their combination significantly raised the BT of normal rats (kept at 28 degrees C) or of HET-exposed rats. Atropine (5 mg/kg, i.p.) abolished the hyperthermic effect of bicuculline in normal and HET-exposed rats. The BT of normal and HET-exposed rat was increased with morphine (1 mg/kg, i.p.) and was reduced with naloxone (1 mg/kg, i.p.). Bicuculline or physostigmine-induced rise in BT of HET-exposed rats was potentiated following cotreatment of physostigmine with morphine. Atropine-induced hypothermia was abolished due to the cotreatment of atropine with morphine with physostigmine but was attenuated with atropine. In normal rats (kept at 28 degrees C), only atropine attenuated (morphine + bicuculline)-induced hyperthermia. L-Dopa + carbidopa or haloperidol did not significantly affect the BT of rats under similar conditions. These results suggest that short-term (2 h) exposure to HET activates the opioidergic neuron, which activates cholinergic activity through the inhibition of GABAergic system and, thus, enhances the BT.

The involvement of muscarinic receptor subtypes in the mediation of hypothermia, tremor, and salivation in male mice

The potency of centrally administered non-selective (atropine and N-methyl scopolamine) and putatively selective muscarinic antagonists (pirenzepine, AF-DX 116 and 4-DAMP) in inhibition of oxotremorine-induced hypothermia, tremor and salivation in male mice has been compared with their potency in vitro in three functional systems, where muscarinic effects are mediated preferentially by M1 (i.e. superior cervical ganglion), M2 (i.e. atrium), and M3 (i.e. ileum) receptors. Atropine, N-methyl scopolamine and 4-DAMP potently abolished the effects of oxotremorine. Pirenzepine abolished tremor and salivation, whereas hypothermia was antagonized partially only. AF-DX 116 had but weak antagonistic effects. Atropine and N-methyl scopolamine were potent antagonists in all three in vitro test systems. High potency was also seen with 4-DAMP, in particular in the ileum preparation. Pirenzepine showed its highest potency in the ganglion preparation. AF-DX 116 was a weak and non-selective antagonist in all three in vitro preparations. Our studies indicate that the muscarinic induction of tremor and salivation may be preferentially mediated by M3 receptors whereas both M2 and M3 receptors may be involved in the mediation of hypothermia. However, the overall conclusion is that compounds with higher receptor subtype selectivity are needed.

Central and peripheral mediation of hypothermia, tremor and salivation induced by muscarinic agonists in mice

Hypothermia, tremor and salivation induced by muscarinic cholinergic agonists were studied in mice. Oxotremorine-M (quarternary agonist) shows high potency after intracerebroventricular administration, but the potency is low after subcutaneous administration. Oxotremorine potency (non-quarternary agonist) is higher after intracerebroventricular administration than after subcutaneous administration. Scopolamine and atropine (non-quarternary antagonists) antagonize oxotremorine-induced effects more potently after intracerebroventricular than subcutaneous administration. The quarternary antagonists N-methylscopolamine (NMS) and N-methylatropine (NMA) potently antagonize oxotremorine-induced salivation after both subcutaneous and intracerebroventricular administration. Hypothermia is antagonized partially (20-40%) over a large dose range after subcutaneous administration. In ex vivo receptor-binding studies of rat brain tissue, oxotremorine, scopolamine and atropine administered subcutaneously dose-dependently displace 3H-oxotremorine-M. Oxotremorine-M and NMS displace 3H-oxotremorine-M by 21% and 35%, respectively; NMA is ineffective.

IN CONCLUSION

Muscarinic cholinergic-mediated tremor is centrally regulated; hypothermia involves both a central and a peripheral component, the peripheral regulation being relatively less important than the central; central and peripheral regulation of salivation are equally important. Penetration of the blood brain barrier by oxotremorine-M and NMS is shown in the ex vivo binding studies.

Anesthesia influences the outcome from experimental spinal cord injury

The effect of anesthesia upon the functional outcome after experimental spinal cord injury (SCI) was studied in 221 rats subjected to graded weight drop contusion in the thoracic cord. Neurologic function was assessed in a blinded fashion for one week after injury using a modification of the method of Tarlov. The post-mortem concentrations of serotonin and its metabolite were measured in injured and surrounding spinal tissues in a subset of animals in order to estimate the survival of descending long-tract axons. In initial studies using non-ventilated animals where body temperature was not controlled (n = 130), halothane anesthesia was associated with significantly better neurologic scores at all levels of injury (50, 100 and 250 g.cm) in comparison to pentobarbital. In a second experiment under these conditions (n = 53) the effect of halothane was observed after a 50 g.cm injury in comparison to both pentobarbital and nitrous oxide. Improved neurologic recovery was accompanied by the preservation of normal serotonin and metabolite concentrations in spinal tissue caudal to the site of injury. These values did not differ from those measured in sham-operated animals. Separate experiments (n = 12) revealed halothane's preservation of somatosensory-evoked responses during the early postinjury period in animals showing improved neurologic recovery. Subsequent experiments (n = 12) were performed to assess the effect of oxygen supplementation and the control of rectal temperature and a separate series of acute experiments (n = 14) examined arterial blood pressure responses to injury in halothane- and pentobarbital-anesthetized animals.(ABSTRACT TRUNCATED AT 250 WORDS)

Neuroleptic malignant syndrome

Five patients with neuroleptic malignant syndrome (NMS) are described. The syndrome developed earlier and took longer to resolve in patients with schizophrenic disorders. Deterioration in the level of consciousness presented earlier than rigidity and fever in all five patients and was thus considered a major criterion. A significant proportion of the patients showed abnormalities of gaze. In four of the five patients spontaneous recovery occurred without the need for specific drugs.

Possible brainstem involvement in the modification of thermoregulatory processes by chlordecone in rats

The involvement of the central nervous system in the hypothermia induced by chlordecone was studied by evaluating the effects of infusions of chlordecone injected into the lateral and third ventricles and the cisterna magna on colonic temperature (Tcol). Compared to rats given vehicle, infusions of 40, 320 or 800 micrograms of chlordecone into the lateral ventricle or 320 or 800 micrograms of chlordecone into the third ventricle, through chronic indwelling cannulae, did not change significantly Tcol. However, intracisternal infusions of 80, 160, 320 or 800 micrograms of chlordecone produced significant hypothermia (maximally 2.2 degrees C) which persisted for as long as 6 hr. Intracisternal infusions of chlordecone also produced a rapid increase in the temperature of the tail skin (Tsk) which persisted throughout the period of hypothermia. This suggests that the hypothermia produced by central administration of chlordecone is related to peripheral vasodilation. Since chlordecone has been reported to induce release of NE in the brainstem, and NE is known to modulate tonic vasomotor control in the medulla, the effects of NE infused intracisternally were studied. Intracisternal infusions of NE (16 micrograms) significantly decreased Tcol and increased Tsk, supporting the hypothesis that hypothermia induced by chlordecone is associated with vasodilatory effects, mediated by an adrenergic mechanism in the brainstem.

Temperature as a dependent variable in the study of cholinergic mechanisms

1. Change in core temperature over time can be used as a dependent variable when studying the effects of manipulations on neurotransmitter systems. This article focuses on the measurement of core temperature as a strategy for detecting changes in the status of cholinergic systems. 2. Cholinergic neurons participate in the process of thermoregulation and interventions affecting them alter the thermal response to cholinomimetics. For example, chronic treatment with amitriptyline, chronic swim stress and inescapable footshock supersensitize rats to the hypothermic effects of oxotremorine. 3. This is consistent with the hypothesis that the pathophysiologies of tricyclic antidepressant withdrawal phenomena and stress involve supersensitivity of muscarinic mechanisms. 4. Uses of thermoregulation paradigms for investigating the actions of lithium ion, electroconvulsive shock and substances of abuse on muscarinic mechanisms are discussed. Applications to problems in the arena of clinical research are highlighted.

Effect of sodium pentobarbital on behavioral thermoregulation in rats and mice

In this study on behavioral thermoregulation, male Sprague-Dawley rats were given intraperitoneal (IP) injections of sodium pentobarbital in doses of 0, 1, 5, 10 or 15 mg/kg and male CBA/J mice were given doses of 0, 5, 10, 15 or 30 mg/kg. The animals were immediately placed in a temperature gradient which allowed them to select their preferred ambient temperature (Ta). The preferred Ta of rats increased following an injection of 10 mg/kg sodium pentobarbital, whereas, the barbiturate had no effect on the preferred Ta of mice. In another study, male rats and mice were given sodium pentobarbital in doses of 0, 5, 10 and 15 mg/kg and then placed into a temperature-controlled environmental chamber set at 30 degrees C for mice and 25 degrees C for rats (i.e., their approximate preferred Ta when dosed with sodium pentobarbital). Colonic temperatures were taken one hour after injection. Sodium pentobarbital induced dose dependent hypothermia in rats at 25 degrees C and hyperthermia in mice at 30 degrees C. These data suggest a direct or indirect block of heat gain/conserving effectors in rats treated with sodium pentobarbital which results in hypothermia and an appropriate compensatory selection of a warmer Ta.

Determination of intraoperative plasma catecholamine concentrations using liquid chromatography with electrochemical detection

Liquid chromatography with electrochemical detection was used for the determination of norepinephrine and epinephrine in human plasma samples obtained prior to, after, and six times during the course of spinal fusion surgery for the correction of scoliosis. The catecholamines were extracted from plasma by alumina adsorption and chromatographed isocratically using a reversed-phase, ion-pairing system. Data obtained are compared to those obtained intraoperatively by other authors using a radioenzymatic method, and the mechanism of sympathetic activation during surgery is discussed. Preliminary data using 3-micron particle size columns and dual-parallel electrochemical detection are presented.

Effects of doxapram on body temperature of the rat during radiofrequency irradiation

Central nervous system stimulants can cause changes in body temperature and changes in susceptibility to high levels of radiofrequency radiation (RFR). In the present study, the effects of the central nervous system stimulant, doxapram, on thermal responses to 2.8 GHz pulsed RFR were examined in anaesthetized rats. During intermittent exposure to an average power density of 60 mW/cm2, doxapram significantly increased the time required for temperature to return to the pre-exposure level when irradiation was discontinued. When exposure was continued until lethal temperatures resulted, doxapram administration caused no significant change in survival time when compared to saline controls. Thus, although the drug decreased thermoregulatory efficiency during intermittent exposure to RFR, no change in susceptibility to terminal RFR exposure was observed.

Restraint alters the thermic response to morphine by postural interference

The effects of morphine on body temperature have been shown to be altered by restraint. The purpose of this study was to determine how the type of restraint alters body temperature measurements and whether restraint alters the effects of morphine on body temperature by interfering with the ability of the rats to adjust their posture. The thermic effects of 5 doses of morphine (3.8 to 45 mg/kg) were compared in two types of restraint and confinement to a 13 X 20 X 20 cm pan without restraint. In unrestrained rats, morphine caused predominantly hyperthermia, but with restraint morphine caused hyperthermia at low doses and hypothermia at higher doses. Morphine hypothermia was greater in rats restrained in a wire-mesh restrainer which prevented heat and humidity build-up than in the commonly used plastic restrainer. In the unrestrained rats, morphine treatment was associated with a posture characterized by exophthalmos, immobility, a hunched position and increased muscle tone. Restrained rats could not assume a compact posture. These results suggest that restraint alters the thermic effect of morphine mainly by interfering with postural mechanisms which reduce heat loss.

Effects of PAM, proPAM, and DFP on behavior, thermoregulation, and brain AChE in rats

The effects of pyridine-2 aldoxime methyl iodide (PAM), N-methyl-1,6-dihydro-pyridine-2-carbaldoxime hydrochloride (proPAM), and diisopropyl phosphorofluoridate (DFP) on performance of a conditioned avoidance response (CAR), body temperature, and in vivo acetylcholinesterase (AChE) activity in five brain regions in the rat were examined. Sublethal doses of DFP (1.5 to 2.5 mg/kg, IP) markedly degraded CAR performance. This effect was antagonized by 5 mg/kg, subcutaneously injected (SC) atropine. A 50 mg/kg, SC dose of PAM had no effect on the CAR, but an equal dose of proPAM caused a transient deterioration of performance. Given 10 min or 2 hr after DFP, 50 mg/kg proPAM initially exacerbated the behaviorally toxic effects of DFP. Neither PAM nor proPAM antagonized DFP-induced hypothermia. PAM did not reactivate DFP-inhibited brain AChE, and proPAM reactivated it by only 6 to 12% of control activity.

Mutual connections of the raphe system and hypothalamus in relation to fever

Previous studies in our laboratory have shown that lesions in certain brain stem regions prevent elevations of body temperature after administration of bacterial pyrogen. In the present experiments wer examined the morphology of the connections of these "brain stem thermoregulatory centers" which are represented in all raphe and paraphe nuclei of the brain stem reticular formation. The methods of anterograde degeneration and tracing of retrograde transport of horseradish peroxidase were used to identify afferent and efferent connections within this "thermoregulatory field." Abundant mutual connections between the raphe nuclei and hypothalamus were found. All nuclei of the raphe system receive afferents from the medial and lateral hypothalamus. All raphe nuclei have efferent projections to the medial reticular formation, and the raphe nuclei of the pons and mesencephalon provide ascending fibers to the hypothalamus. A lesion of any part (origin, course, termination field) of this mutual raphe-hypothalamic pathway system will prevent development of fever in response to bacterial pyrogen.

Effect of delta 9-tetrahydrocannabinol on hypothalamic thermosensitive units

Thermosensitive anterior hypothalamic neurons (pre-optic region) were studied in urethane and chloralose anesthetized cats in an attempt to characterize the hypothermic action of delta 9-THC at the neuronal level. One hundred and seventy-eight single neurons were isolated and subjected to thermal challenge, 66 were found to reproducibly alter firing frequency at a significant level (thermosensitivity (T.S.) greater than 0.75). Twenty-one of these units met the criteria for primary thermodetectors, 34 were heat-sensitive interneurons, and 11 were cold-sensitive interneurons. Administration of delta 9-THC (1.0-2.0 mg/kg i.v.) decreased the spontaneous firing and increased the T.S. of the primary thermodetector units. delta 9-THC also increased the spontaneous firing frequency as well as the T.S. of heat-sensitive interneurons, while decreasing both the T.S. and spontaneous firing of cold-sensitive interneurons. The decreased spontaneous firing of primary thermodetectors could result from altered facilitory or inhibitory influences converging on these cells. The increased thermosensitivity is consistent with the hypothesis that the pre-optic region modulates cannabinoid-induced hypothermia.

Forced swimming in rats: hypothermia, immobility and the effects of imipramine

Rats when forced to swim in a restricted space not only became immobile but showed marked hypothermia. The hypothermia was greater than that observed after reserpine or Ro 4-1284 and was not antagonized by imipramine at doses which significantly reduced immobility. Hypothermia induced by forced swimming can therefore be dissociated from the immobility occurring in these conditions and also from drug-induced hypothermia.

Hyperthermia evoked by the intracerebral injection of morphine sulphate in the rat: the effect of restraint

Morphine sulphate (M) was microinjected intracerebrally into 26 sites in the free-moving and 11 sites in the restrained rat. The injections were made into the preoptic-anterior hypothalamic (POAH) region as core temperature (Tc) was measured. A marked increase in Tc was evoked from the free-moving rat following doses of M of 1 (n = 10); 10 (n = 19); 20 (n = 7); or 50 microgram (n = 6). On the other hand, no increase in Tc significantly above the control level was observed in the restrained rat following the intracerebral administration of M in doses of 10 (n = 8), 20 (n = 9), 50 (n = 10), or 70 microgram (n = 4). The control injection of the artificial cerebrospinal fluid (5-ion), used as the drug vehicle, caused a mild hyperthermia about 1.0 degrees C above the baseline level in both the free-moving and restrained rat. We conclude that morphine evokes a hyperthermia by its action on POAH neurons, but the M-induced hyperthermia can be attenuated by restraining the rat.

Changes in rectal temperature of the rabbit by intracerebroventricular injection of bradykinin and related kinins

The effects of intracerebrovascular injections of bradykinin (BK), lysyl-bradykinin (L-BK), methionyl-lysyl-bradykinin (ML-BK) and des-arginyl-bradykinin (Des-Arg9-BK) on the rectal temperature of rabbits were investigated. A linear dose-response curve could be obtained with bradykinin. Equimolar doses to BK of L-BK and ML-BK gave responses of the rectal temperature undistinguishable from those of BK. In contrast, the smaller polypeptide Des-Arg9-BK did not show any hyperthermic properties. Since prostaglandins (PG) are known to potentiate (facilitate) the peripheral effects of BK and display a hyperthermic action, their synthesis being inhibited by antipyretics, we studied the effect of indomethacin and paracetamol on the BK-induced rise in rectal temperature in rabbits. It could be shown that these drugs inhibited partially the response to BK. The possible participation of BK in thermoregulation will be discussed.

Are there 2 cholinergic thermoregulatory centres in rats?

An attempt was made to replicate the conflicting previous reports of hypo- and hyperthermic effects of intrahypothalamically administered carbachol. Despite using the same coordinates, injection parameters, and strain of rats reported by others, only hypothermia was conclusively demonstrated. It was concluded that the cholinergic system mediates heat loss mechanisms in rats.

Hypothermia induced by delta9-tetrahydrocannabinol in rats with electrolytic lesions of preoptic region

The preoptic region (POR) is a primary central site for thermoregulation. Bilateral lesions of POR disrupt thermoregulation, and in rats, produce a characteristic syndrome including hyperthermia. delta9-Tetrahydrocannabinol (delta9-THC), a potent hypothermic agent, appears to mediate this effect via some central mechanism. The studies reported here suggest that delta9-THC induces hypothermia at a site other than POR. Male Sprague-Dawley rats were divided into 2 groups, one with subsequently confirmed bilateral POR lesions and a sham operated group. The lesioned animals developed hyperthemia (+2.1degrees +/- 0.1degreesC, p less than 0.01) within 2 hr after surgery when compared to the sham operated controls. delta9-THC was administered intraperitoneally (5 and 10 mg/kg). Rectal temperature was recorded at 30 min intervals for 2.5 hr. Both lesioned and nonlesioned rats exhibited hypothermia within 30 min of delta9-THC administration. The hypothermic response to 5 and 10 mg/kg delta9-THC in the lesioned animals was significantly greater (p less than 0.05) and showed a trend toward longer duration than the hypothermia induced in the sham operated controls. These data demonstrate that delta9-THC is able to induce a hypothermic response in rats whose body temperatures were elevated by POR ablation. Although delta9-THC does not appear to act primarily at POR to induce hypothermia, it is evident than an intact POR plays a role in modifying the duration and magnitude of delta9-THC induced hypothermia.

Heat-escape behavior in the rat following intrahypothalamic injection of acetylcholine

The effects of preoptic/anterior hypothalamic injections of acetylcholine on heat-escape behavior and hypothalamic temperature were investigated in unrestrained rats implanted with bilateral cannulae. Two types of responses were observed, either a fall in hypothalamic temperature coupled with an increase in behavioral responses to escape heat or a rise in hypothalamic temperature associated with little or no change in behavioral heat-escape responses. The fall in hypothalamic temperature observed in one group of rats was significant and was associated with a dose-dependent increase in heat-escape responding. The rise in hypothalamic temperature noted in the other group of rats was nonsignificant, and the associated behavioral responses were variable. Distinct anatomical differences in cannulae loci between the 2 groups were not apparent. It is concluded that acetylcholine activates the heat-dissipating control system of the rat hypothalamus and that the hyperthermic effects of acetylcholine are nonspecific.

Effects of atropine, injected into a lateral cerebral ventricle of the rabbit, on fevers due to intravenous leucocyte pyrogen and hypothalamic and intraventricular injections of prostaglandin E1

1. Cholinergic synapses in the hypothalamus may transmit information in those thermoregulatory pathways which function to raise body temperature. The effect of atropine, administered intracranially, on the febrile response to intravenous leucocyte pyrogen or intracranial prostaglandin E1 was therefore examined in conscious rabbits. 2. In rabbits exposed to a thermoneutral environment, micro-injections of PGE1, into the anterior hypothalamus, intraventricular injections of PGE1, and intravenous injection so leucocyte pyrogen all caused fever accompanied by vasoconstriction in the ears and reduced respiratory rate. Intraventricular injection of 200 mug atropine during such fevers attenuated their development. This was due to the activation of heat loss mechanisms through vasodilatation in the ears and an increase in the frequency of respiration. This suggests a similarity in the pattern of neuronal activity evoked by PGE1 and leucocyte pyrogen, at least at the site(s) where atropine directly or indirectly exerted its effect and in the efferent pathways from this site. 3. In rabbits exposed to a cold environment, intraventricular injection of PGE1 caused fever through the activation of shivering accompanied by increased O2 consumption. Intraventricular injection of atropine during the development of fever caused an inhibition of shivering accompanied by increased O2 consumption. Intraventricular injection of atropine during the development of fever caused an inhibition of shievering and a decrease in O2 consumption so that temperature ceased to rise and returned to normal. 4. During fever, reversal by atropine of the increased heat conservation of rabbits in a neutral environment, and of their increased heat production in a cold environment adds further support to the concept that cholinergic synapses provide an important link in central temperature-rasising pathways.

Hypothermic and toxic actions of 2-butyne-1, 4-diol and other related diols in the rat

The effects of 2-butyne-1,4-diol (BYDL) and related congeners on the body temperature of the rat have been determined. BYDL, at doses above 0·4 mmol kg−1 intraperitoneally, produced a significant fall in body temperature which was dose dependent. 2-butene-1,4-diol (BEDL) had no hypothermic action, and butane-1,4-diol (BDL) produced only a moderate fall in temperature (1·9°) which correlated with the time course of the hypnotic effect of the drug. γ-Butyrolac-tone (GBL), γ-hydroxybutyric acid (GHB) and pentobarbitone at hypnotic doses had similar hypothermic actions which correlated with the period of hypnosis. The hypothermia produced by BYDL could not be prevented by pretreatment with scopolamine or by maintaining the rats at high environmental temperature (32°). BYDL was far more toxic than the other diols examined (LD50 = 0·609-0·635 mmol kg−1 compared to BEDL: 3·71-3·74 mmol kg−1 and BDL: 11·87-11·90 mmol kg−1). Pretreatment of rats with pyrazole, an inhibitor of liver alcohol dehydrogenase, prevented the toxic and hypothermic actions of BYDL. From earlier studies with pyrazole and BDL it was concluded that BYDL itself was not active but that it was possibly converted in vivo by liver alcohol dehydrogenase to a toxic metabolite.