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A study of the reciprocal relationship between the thermal and behavioral effects mediated by anandamide
... The means for each phase of the photoperiod were calculated for comparison and to confirm that the experimental arrangement was in agreement with the nocturnal habits described for Wistar rats. Hourly means were also calculated to confirm the oscillation of T b and SLA [27]. In addition, these averages were used to further study the correlation between these two parameters throughout the day and with exercise capacity. ...
... Notably, many physiological parameters, such as T b , SLA and heart rate, interact in distinct ways across the daily cycle [6]. We have recently shown that the pharmacological manipulation of the CNS can dissociate the relationship between SLA and T b [27]. Freerunning rhythms of T b and heart rate were shown to be independent of SLA in the SCN (the major site responsible for information processing and integration regarding circadian oscillators) of lesioned and intact rats [8]. ...
The aim of this study was to verify the possible interactions between exercise capacity and spontaneous locomotor activity (SLA) during the oscillation of core body temperature (Tb) that occurs during the light/dark cycle. Wistar rats (n=11) were kept at an animal facility under a light/dark cycle of 14/10 h at an ambient temperature of 23 °C and water and food ad libitum. Initially, in order to characterize the daily oscillation in SLA and Tb of the rats, these parameters were continuously recorded during 24 h using an implantable telemetric sensor (G2 E-Mitter). The animals were randomly assigned to two progressive exercise test protocols until fatigue during the beginning of light and dark-phase. Fatigue was defined as the moment rats could not keep pace with the treadmill. We assessed the time to fatigue, workload and Tb changes induced by exercise. Each test was separated by 3 days. Our results showed that exercise capacity and heat storage were higher during the light-phase (p<0.05). In contrast, we observed that both SLA and Tb were higher during the dark-phase (p<0.01). Notably, the correlation analysis between the amount of SLA and the running capacity observed at each phase of the daily cycle revealed that, regardless of the time of the day, both types of locomotor physical activity have an important inherent component (r=0.864 and r=0.784, respectively, p<0.01) without a direct relationship between them. This finding provides further support for the existence of specific control mechanisms for each type of physical activity. In conclusion, our data indicate that the relationship between the body temperature and different types of physical activity might be affected by the light/dark cycle. These results mean that, although exercise performance and spontaneous locomotor activity are not directly associated, both are strongly influenced by daily cycles of light and dark.
Copyright © 2014. Published by Elsevier Inc.
... Interactions with other monoamine receptors, together with non-monoamine receptors activated by acetylcholine, glutamate, cannabinoids, and neuropeptides may also mediate therapeutic effects of antipsychotic agents. Interactions with receptors associated with these neurotransmitters may also have marked thermoregulatory effects, as demonstrated, for example, for cannabinoid receptors (Lima et al. 2014;Smirnov and Kiyatkin 2008). ...
Rationale:
We recently introduced a new rat model of emotional hyperthermia in which a salient stimulus activates brown adipose tissue (BAT) thermogenesis and tail artery constriction. Antipsychotic drugs, both classical and second generation, act to reduce excessive assignment of salience to objects and events in the external environment. The close association between salient occurrences and increases in body temperature suggests that antipsychotic drugs may also reduce emotional hyperthermia.
Objectives:
We determined whether chlorpromazine, clozapine, and risperidone dose dependently reduce emotionally elicited increases in BAT thermogenesis, cutaneous vasoconstriction, and body temperature in rats.
Methods:
Rats, chronically instrumented for measurement of BAT and body temperature and tail artery blood flow, singly housed, were confronted with an intruder rat (confined within a small wire-mesh cage) after systemic pre-treatment of the resident rat with vehicle or antipsychotic agent. BAT and body temperatures, tail blood flow, and behavioral activity were continuously measured.
Results:
Clozapine (30 μg-2 mg/kg), chlorpromazine (0.1-5 mg/kg), and risperidone (6.25 μg-1 mg/kg) robustly and dose-relatedly reduced intruder-elicited BAT thermogenesis and tail artery vasoconstriction, with consequent dose-related reduction in emotional hyperthermia.
Conclusions:
Chlorpromazine, a first-generation antipsychotic, as well as clozapine and risperidone, second-generation agents, dose-dependently reduce emotional hyperthermia. Dopamine D2 receptor antagonist properties of chlorpromazine do not contribute to thermoregulatory effects. Interactions with monoamine receptors are important, and these monoamine receptor interactions may also contribute to the therapeutic effects of all three antipsychotics. Thermoregulatory actions of putative antipsychotic agents may constitute a biological marker of their therapeutic properties.
... The resting protocol consisted of staying on the treadmill for 90 min. During the second experimental session 90 min after fatigue (Lima et al., 2014b;Santiago et al., 2016; for a short review of c-fos protein expression, please refer to Kovàcs, 1998), animals were deeply anesthetized with ketamine and xylazine and were transcardially perfused with 40 mL of heparinized 0.01 M phosphate-buffered saline (PBS), followed by 400 mL of 4% paraformaldehyde (PFA) in 0.2 M phosphatebuffered saline (pH 7.4). The brains were removed for subsequent immunohistochemical analysis. ...
In the present study, we investigated whether the daily fluctuations of internal body temperature (Tb) and spontaneous locomotor activity (SLA) interact with the thermal and neuronal adjustments induced by high-intensity aerobic exercise until fatigue. The body temperature and SLA of adult Wistar rats (n = 23) were continuously recorded by telemetry for 48 h. Then, the rats were subjected to a protocol of graded exercise until fatigue or rest on the treadmill during light and dark-phases. Tb, tail skin temperature and ambient temperature during each experimental session were recorded. At the end of the last experimental session, the animals were anaesthetized; the brains were perfused and removed for immunohistochemical analysis of c-fos neuronal activation. The daily rhythms of SLA and Tb were strongly correlated (r = 0.88 and p < 0.001), and this was followed by a daily oscillation in both the ratio and the correlation index between these variables (p < 0.001). Exercise capacity was associated with a lower resting Tb (p < 0.01) and was higher in the light-phase (p < 0.001), resulting in an increased capacity to accumulate heat during exercise (p < 0.01). Independent of time-of-day, high intensity exercise strongly activated the hypothalamic paraventricular nucleus (PVN), the supra-optic nucleus (SON) and the locus coeruleus (LC) (p < 0.001) but not the suprachiasmatic nucleus (SCN). Taken together, our results points toward a role of the circadian system in a basal activity control of the thermoregulatory system as an important component for the onset of physical activities. In fact, rather than directly limiting the adjustments induced by exercise the present study brings new evidence that the effect of time-of-day on exercise performance occurs at the threshold level for each thermoregulatory system effector activity. This assumption is based on the observed resilience of the central clock to high-intensity exercise and the similarities in exercise-induced neuronal activation in the PVN, SON, and LC.
Anxiety resulting from psychogenic stimuli elicit stress-induced hyperthermia in rats, often called “psychogenic fever”, which is part of a coordinated response to situations seen as novel or distressing. Brain transient receptor potential vanilloid 1 (TRPV1) channels modulate both thermoregulation and animal behavior; however, the role of peripheral TRPV1 channels in regulating these responses during exposure to an anxiogenic environment has not been determined. Thus, the present study aimed to investigate the involvement of abdominal TRPV1 channels in stress-induced hyperthermia and behavior in rats subjected to an unconditioned anxiety test. Desensitized rats (peripheral desensitization of TRPV1 channels with resiniferatoxin; RTX) and their respective controls were subjected to a 15-min open field (OF) test. The core body temperature (Tcore), tail skin temperature (Tskin), and rats’ movements inside the arena were recorded. The OF test induced a similar increase in Tcore in both groups throughout the exposure time; however, at the recovery period, the RTX-treated rats had a slower reduction in Tcore due to lower tail skin heat loss. Tskin decreased significantly in both groups during exposure to OF but, during recovery, the RTX-treated rats showed impaired skin vasodilation. Also, RTX-treated rats entered fewer times and spent less time in the OF center square, suggesting an anxiety-related behavior. Our findings indicate that, under stressful conditions, peripheral TRPV1 channels modulate thermoregulatory and behavioral responses. The TRPV1 desensitization induces a more prolonged hyperthermic response due to lower cutaneous heat dissipation, alongside a more evident anxiety-like behavior in rats subjected to the OF apparatus.
Circadian rhythms are 24-h cycles in physiology regulated by the suprachiasmatic nucleus (SCN) in the brain, where daily cues act on SCN neurons to alter clock timing. Cannabinoid signaling modulates SCN neuronal activity, although the mechanism remains unclear. We propose that neuronal activity generates endocannabinoid release, activating astrocyte Ca2+ signaling, which releases adenosine and activates adenosine-1 receptors (A1Rs) on the presynaptic axon terminals, decreasing GABA release. We demonstrated, in mice, that activation of cannabinoid-1 receptors (CB1R) with the agonist WIN 55,212-2 (WIN) reduced the miniature GABA receptor-mediated postsynaptic current (mGPSC) frequency by a mechanism that requires astrocytes and A1R. WIN activated an intracellular Ca2+ signaling pathway in astrocytes. Activating this intracellular Ca2+ pathway with designer receptors exclusively activated by designer drugs (DREADDs) also decreased the mGPSC frequency and required A1R activation. The frequency of spontaneous Ca2+ events, including those induced by depolarization of a postsynaptic SCN neuron, was reduced by blocking CB1R activation with AM251, demonstrating neuronal endocannabinoid signaling modulates astrocytic Ca2+ signaling in the SCN. Finally, daytime application of WIN or adenosine phase advanced the molecular circadian clock, indicating that this cannabinoid signaling pathway is vital for the timing of circadian rhythms.
Rectal temperature of 10 female adult horses was recorded every 2 h for 10 consecutive days under a natural winter photoperiod (9 h of light and 15 h of darkness per day). A robust daily rhythm of body temperature was observed in all animals. The rhythm had a mean level of 38.3°C and a range of excursion of 1.0°C. Temperature started its daily ascent at dawn each day and reached a maximum 14 hours later. Body temperature of 5 of the horses was studied for 10 more days under constant illumination. The rhythm persisted under this condition, although with a slightly longer period of 24.2 h, which confirms the endogenous nature of the rhythm. Despite the fact that the body size of the horse is several orders of magnitude greater than that of rodents, the various parameters of the body temperature rhythm of the horse are similar to those of several species of rodents previously studied.
Currently available methods for the analysis of circadian rhythms provide little help in the evaluation of the circadian rhythm
of body temperature because they either assume that the circadian rhythm of body temperature approximates a cosine wave (which
for many species is not true) or simply do not address important parameters, such as the amplitude and the shape of the temperature
rhythm. The present paper presents methods for the computation and statistical evaluation of the period, amplitude, mean level,
and general shape of the circadian rhythm of body temperature. The period is analyzed by the periodogram procedure, whereas
the other parameters are analyzed by the histogram method. Both procedures are simple to implement and relatively insensitive
to spurious data points. A simplified but fully operational program in BASIC is provided.
In mammals, thermoregulation is a key feature in the maintenance of homeostasis. Thermoregulatory capacities are strongly related to energy balance and animals are constantly seeking to limit the energy costs of normothermia. In case of thermal changes, physiological mechanisms are enhanced, increasing rates of energy expenditure. However, behavioral adjustments are available for species to lower the autonomic work, and thus reduce the energy costs of thermoregulatory responses. Hence, thermogenesis-induced metabolic costs can be reduced during cold exposure, and hyperthermia associated to dehydration can be avoided during heat exposure. Hypothermia avoidance consists in a concomitant decrease in heat dissipation and increase in heat production. Inversely, heat exchange is enhanced and body heat production is reduced when avoiding hyperthermia. The different behavioral strategies available for mammal species to cope with both decreased and increased levels of ambient temperature are reviewed. Moreover, thermoregulation function is under the control of central, metabolic, energetic and endocrine systems, which induces that parameters such as hour of the day, season, gender or aging may affect thermoregulatory adjustments. Some examples will be given.
Central neural circuits orchestrate a homeostatic repertoire to maintain body temperature during environmental temperature challenges and to alter body temperature during the inflammatory response. This review summarizes the functional organization of the neural pathways through which cutaneous thermal receptors alter thermoregulatory effectors: the cutaneous circulation for heat loss, the brown adipose tissue, skeletal muscle and heart for thermogenesis and species-dependent mechanisms (sweating, panting and saliva spreading) for evaporative heat loss. These effectors are regulated by parallel but distinct, effector-specific neural pathways that share a common peripheral thermal sensory input. The thermal afferent circuits include cutaneous thermal receptors, spinal dorsal horn neurons and lateral parabrachial nucleus neurons projecting to the preoptic area to influence warm-sensitive, inhibitory output neurons which control thermogenesis-promoting neurons in the dorsomedial hypothalamus that project to premotor neurons in the rostral ventromedial medulla, including the raphe pallidus, that descend to provide the excitation necessary to drive thermogenic thermal effectors. A distinct population of warm-sensitive preoptic neurons controls heat loss through an inhibitory input to raphe pallidus neurons controlling cutaneous vasoconstriction.
Δ ⁹ ‐Tetrahydrocannabinol (Δ ⁹ ‐THC) was injected into the preoptic area of the anterior hypothalamus or into the third or fourth cerebral ventricle of the conscious mouse through a chronically implanted cannula and the effects on body temperature and oxygen consumption rate were measured.
At an ambient temperature of 22°C, injections of Δ ⁹ ‐THC into the fourth ventricle (5 and 10 μg) produced dose‐dependent falls in rectal temperature. Hypothermia was also observed after injections of the drug into the hypothalamus (5 and 10 μg) or into the third ventricle (10 μg).
The hypothermia produced by Δ ⁹ ‐THC was associated with a fall in oxygen consumption rate. Falls in rectal temperature and in oxygen consumption rate were significantly greater after injection of Δ ⁹ ‐THC than after injection of the drug vehicle, Tween 80.
The falls in rectal temperature and oxygen consumption rate produced by injection of Δ ⁹ ‐THC into the fourth ventricle were abolished by elevation of the ambient temperature from 22 to 32°C.
A pretreatment that consisted of subcutaneous injections of Δ ⁹ ‐THC (20 mg/kg) given once daily for three days produced tolerance to the hypothermic effect of the drug when injected on day 4 either into the fourth ventricle (10 μg) or into a lateral tail vein (2.0 mg/kg).
The results suggest that Δ ⁹ ‐THC acts centrally to alter thermoregulation in mice not only when it is injected directly into the hypothalamus or cerebral ventricles but also when it is given intravenously. After intraventricular or intravenous administration the drug may act at extrahypothalamic as well as at hypothalamic sites. The data also support the hypothesis that in mice, tolerance to the hypothermic effect of Δ ⁹ ‐THC is pharmacodynamic and does not depend on changes in metabolism or distribution of the drug.
1. Arachidonylethanolamide (AEA; anandamide) has been isolated from mammalian brain and found to bind to, and is thought to be, an endogenous ligand for the cannabinoid receptor. In order to understand better its behavioural and physiological properties, we have examined its acute effects in unanaesthetized freely behaving rats. 2. Intravenous AEA caused dose-related decreases in locomotor behaviour, a pronounced hyperreflexia, and a moderate antinociceptive state. At doses between 3 and 30 mg kg-1, a dose-dependent hypothermia and profound, time-dependent cardiovascular changes were also observed. 3. An immediate bradycardia exceeding 50% was seen within 10-15 s of administration and lasted up to 11 min following the highest dose of the drug. In contrast, the change in mean arterial pressure was biphasic: an immediate 20% decrease in mean arterial pressure followed by a significant increase in blood pressure that lasted about 13 min after the highest dose. 4. These data demonstrate that AEA in the unanaesthetized rat exerts behavioural and physiological effects generally similar to those seen following natural cannabinoids and synthetic cannabimimetic agents and suggests a role for AEA in regulation of various physiological processes.
Central cannabinoid systems have been implicated in appetite regulation by the respective hyperphagic actions of exogenous cannabinoids, such as delta9-THC, and hypophagic effects of selective cannabinoid receptor antagonists.
This study examined whether an endogenous cannabinoid, anandamide, could induce overeating, via a specific action at central (CB1) cannabinoid receptors.
Pre-satiated male rats (n=18), received subcutaneous injections of anandamide (0.5, 1.0, 5.0, 10.0 mg/kg) before 3-h, nocturnal food intake tests. In a second series of intake tests (n=8), anandamide injection (1.0 mg/kg) was preceded by injection of the specific CB1 receptor antagonist, SR141716 (0.1, 0.5, 1.0 mg/kg SC).
All doses of anandamide induced significant overeating, with 1.0 mg/kg being most potent. Additionally, hyperphagia induced by 1.0 mg/kg anandamide was dose-dependently attenuated by SR141716 pretreatment.
This first demonstration of anandamide-induced, CB -mediated, overeating provides important evidence for the involvement of a central cannabinoid system in the normal control of eating.
In the absence of any specific behavioral assay for cannabinoids or endocannabinoids, a cannabinoid-induced profile in a series of four in vivo assays in mice is most commonly used to assess a specific cannabinoid activity at the behavioral level. Thus, when a given compound produces motor depression in an open field, catalepsy on an elevated ring, analgesia on a hot plate, as well as hypothermia, cannabinoid CB1 receptor activation is assumed, although exceptions are possible. The full cannabinoid profile, however, includes for example ataxia in dogs and discrimination learning in rats. In view of (1) the addictive/reward potential of cannabis and the cannabinoids and (2) the multiple roles of the endocannabinoid physiological control system (EPCS) in behavioral functions, including memory, emotionality, and feeding, a number of behavioral techniques have been used to assess the effects of cannabinoids in these functions. In this chapter we will describe the tetrad of cannabinoid-induced effects as well as a series of behavioral assays used in the behavioral pharmacology of marijuana-cannabinoid research. Since the EPCS plays an important role in the developing organism, methods used in the assessment of physical and behavioral development will also be discussed. The techniques include the tetrad, drug discrimination, self-stimulation and self-administration, conditioned place preference/aversion, the plus-maze, chronic mild stress (CMS), ultrasonic vocalizations, cognitive behaviors, and developmental assessment in mouse (and rat) pups.
Immunohistochemical distribution of cannabinoid receptors in the adult rat brain was studied using specific purified antibodies against the amino-terminus of the CB1 receptor. Our results generally agree well with the previous studies using CB1 receptor autoradiography and messenger RNA in situ hybridization. However, because of its greater resolution, immunohistochemistry allowed identification of particular neuronal cells and fibers that possess cannabinoid receptors. CB1-like immunoreactivity was found in axons, cell bodies and dendrites, where it appeared as puncta in somata and processes. Both intensely and moderately or lightly stained neurons were observed. The intensely stained neurons were dispersed and only occur in cortical structures including hippocampal formation and olfactory bulb. Moderately or lightly stained neurons were found in caudate-putamen and amygdala. In the hippocampal formation only intensely stained neurons were observed. The cell bodies of pyramidal neurons in CA1 and CA3 fields appeared to be unstained but surrounded by a dense plexus of immunoreactive fibers. The granule cells in the dentate area were also immunonegative. Many intensely stained neurons were located at the base of the granule cell layer. CB1-like immunoreactive neurons and fibers were also found in the somatosensory, cingulate, perirhinal, entorhinal and piriform cortices, in claustrum, amygdaloid nuclei, nucleus accumbens and septum. Beaded immunoreactive fibers were detected in periaqueductal gray, nucleus tractus solitarius, spinal trigeminal tract and nucleus, dorsal horn and lamina X of the spinal cord. A triangular cap-like mass of immunoreactivity was found to surround the basal part of the Purkinje cell body in the cerebellum. Only small, lightly stained cells were found in the molecular layer in the cerebellum close to the Purkinje cell layer. The CB1 receptor is widely distributed in the forebrain and has a more restricted distribution in the hindbrain and the spinal cord. It appears to be expressed on cell bodies, dendrites and axons. According to the location and morphology, many, but not all, CB1-like immunoreactive neurons appear to be GABAergic. Therefore, cannabinoids and cannabinoid receptors may play a role in modulating GABAergic neurons.
Anandamine (arachidonylethanolamide), an arachidonic acid derivative isolated from the porcine brain, displays binding characteristics indicative of an endogenous ligand for the cannabinoid receptor. The functional activity of anandamide was tested in vivo using behavioral and physiological paradigms in laboratory rodents. At IP doses from 2 to 20 mg/kg in mice, anandamide significantly decreased spontaneous motor activity in a Digiscan open field. Rectal body temperature significantly decreased at doses of 10 and 20 mg/kg in rats. At doses from 0.03 to 30 mg/kg, anandamide had no significant effect on chow consumption in ad lib fed rats. Over the dose range of 2–20 mg/kg, anandamide did not show anxiolytic properties in the mouse light ⇌ dark exploration model of anxiety. Over the dose range of 0.3–3 mg/kg, anandamide had no effect on choice accuracy or session duration in the delayed nonmatching to sample memory task (DNMTS) in rats. These results demonstrate that anandamide has biological and behavioral effects in awake rodents, some of which are similar to the reported actions of THC.
Endocannabinoids (anandamide and 2-AG) are relevant modulators of appetite and energy expenditure through their action on cannabinoid CB(1) receptors. The actions of anandamide on feeding behavior are dependent both, on the anatomical location of CB(1) receptors (central nervous system versus peripheral tissues) and the feeding status. Anandamide uptake into cells, prior to its degradation by specific enzymatic systems, is a necessary step for the regulation of its extracellular levels. The present study explores the route and feeding stimulus dependency of the effects of the anandamide uptake blocker AM404. Peripherally, AM404 reduced feeding in partially satiated animals through a PPARα-independent mechanism, but not in food deprived ones. When AM404 was injected into the cerebral ventricles of food deprived rats, it resulted in hyperphagia that was antagonized by the cannabinoid receptor inverse agonist SR141716A. These results support the multimodal action of endocannabinoid signaling in feeding regulation, which depends on the anatomical site and the feeding status of the animal.
Hypothermia occurs in the most severe cases of systemic inflammation, but the mechanisms involved are poorly understood. This study evaluated whether the hypothermic response to bacterial lipopolysaccharide (LPS) is modulated by the endocannabinoid anandamide (AEA) and its receptors: cannabinoid-1 (CB1), cannabinoid-2 (CB2) and transient receptor potential vanilloid-1 (TRPV1). In rats exposed to an ambient temperature of 22 degrees C, a moderate dose of LPS (25-100 mu g kg-1 i.v.) induced a fall in body temperature with a nadir at similar to 100 min postinjection. This response was not affected by desensitization of intra-abdominal TRPV1 receptors with resiniferatoxin (20 mu g kg-1 i.p.), by systemic TRPV1 antagonism with capsazepine (40 mg kg-1 i.p.), or by systemic CB2 receptor antagonism with SR144528 (1.4 mg kg-1 i.p.). However, CB1 receptor antagonism by rimonabant (4.6 mg kg-1 i.p.) or SLV319 (15 mg kg-1 i.p.) blocked LPS hypothermia. The effect of rimonabant was further studied. Rimonabant blocked LPS hypothermia when administered i.c.v. at a dose (4.6 mu g) that was too low to produce systemic effects. The blockade of LPS hypothermia by i.c.v. rimonabant was associated with suppression of the circulating level of tumour necrosis factor-alpha. In contrast to rimonabant, the i.c.v. administration of AEA (50 mu g) enhanced LPS hypothermia. Importantly, i.c.v. AEA did not evoke hypothermia in rats not treated with LPS, thus indicating that AEA modulates LPS-activated pathways in the brain rather than thermoeffector pathways. In conclusion, the present study reveals a novel, critical role of brain CB1 receptors in LPS hypothermia. Brain CB1 receptors may constitute a new therapeutic target in systemic inflammation and sepsis.
The effects of centrally administered cannabinoids on body core temperature (Tc) and the contribution of endogenous cannabinoids to thermoregulation and fever induced by lipopolysaccharide (LPS) (Sigma Chem. Co., St. Louis, MO, USA) were investigated.
Drug-induced changes in Tc of male Wistar rats were recorded over 6 h using a thermistor probe (Yellow Springs Instruments 402, Dayton, OH, USA) inserted into the rectum.
Injection of anandamide [(arachidonoylethanolamide (AEA); Tocris, Ellisville, MO, USA], 0.01-1 microg i.c.v. or 0.1-100 ng intra-hypothalamic (i.h.), induced graded increases in Tc (peaks 1.5 and 1.6 degrees C at 4 h after 1 microg i.c.v. or 10 ng i.h.). The effect of AEA (1 microg, i.c.v.) was preceded by decreases in tail skin temperature and heat loss index (values at 1.5 h: vehicle 0.62, AEA 0.48). Bell-shaped curves were obtained for the increase in Tc induced by the fatty acid amide hydrolase inhibitor [3-(3-carbamoylphenyl)phenyl] N-cyclohexylcarbamate (Cayman Chemical Co., Ann Arbor, MI, USA) (0.001-1 ng i.c.v.; peak 1.9 degrees C at 5 h after 0.1 ng) and arachidonyl-2-chloroethylamide (ACEA; Tocris) (selective CB(1) agonist; 0.001-1 microg i.c.v.; peak 1.4 degrees C 5 h after 0.01 microg), but (R,S)-(+)-(2-Iodo-5-nitrobenzoyl)-[1-(1-methyl-piperidin-2-ylmethyl)-1H-indole-3-yl] methanone (Tocris) (selective CB(2) agonist) had no effect on Tc. AEA-induced fever was unaffected by i.c.v. pretreatment with 6-Iodo-2-methyl-1-[2-(4-morpholinyl)ethyl]-1H-indole-3-yl](4-methoxyphenyl) methanone (Tocris) (selective CB(2) antagonist), but reduced by i.c.v. pretreatment with N-(piperidin-1-yl)-5-(4-iodophenyl)-1-(2,4-dichlorophenyl)-4-methyl-1H-pyrazole-3-carboxamide (AM251; Tocris) (selective CB(1) antagonist). AM251 also reduced the fever induced by ACEA or LPS.
The endogenous cannabinoid AEA induces an integrated febrile response through activation of CB(1) receptors. Endocannabinoids participate in the development of the febrile response to LPS constituting a target for antipyretic therapy.
Evidence implicates anandamide in dopamine-related cocaine function. In the present study, we investigated the effect of methanandmide (5 mg/kg, i.p.), a stable anandamide analog, on the hyperthermia and hyperactivity induced by a fixed dose of cocaine (15 mg/kg, i.p.). Cocaine administered to rats produced hyperthermia and hyperactivity whereas methanandamide was ineffective. For combined administration, methanandamide attenuated the hyperthermia, but not hyperactivity, induced by cocaine. The effect of methanandamide was abolished by pretreatment with a cannabinoid CB1 receptor antagonist, SR141716A (5 mg/kg, i.p.), or dopamine D2 receptor antagonist, S(-)-raclopride (5 mg/kg, i.p.) but not by capsazepine (40 mg/kg, i.p.), a transient receptor potential vanilloid 1 cation channel antagonist. Methanandamide also attenuated the hyperthermia caused by a dopamine D1 receptor agonist, SKF 38393 (10 mg/kg, s.c.), indicating that it reduces hyperthermia produced by dopamine D1 receptor activation. URB597 (0.25 mg/kg, i.p.), an inhibitor of anandamide metabolism, did not alter cocaine-induced hyperthermia. Our results demonstrate that methanandamide activates cannabinoid CB1 receptors to attenuate cocaine-induced hyperthermia, and that dopamine D2 receptor activation plays a permissive role in the thermoregulatory effects of methanandamide.
The effects of i.v. injected delta9-tetrahydrocannabinol (delta9-THC) on behaviour, body temperature and levels of brain monoamines, measured spectrophotofluorimetrically, of the rat were determined. Doses of delta9-THC in the range of 0.05--5.0 mg/kg produced biphasic changes in behaviour, body temperature and levels of 5-hydroxyindoleacetic acid (5-HIAA). The whole brain levels of dopamine (DA), noradrenaline (NA) and 5-hydroxytryptamine (5-HT) were not altered by delta9-THC. The subjective behavioural biphasic responses did not appear to be dose related, whereas the biphasic changes in body temperature and brain levels of 5-HIAA were dose-related. Low doses of delta9-THC (0.05 and 0.1 mg/kg) caused hyperthermia, while doses of 1.0, 2.0 and 5.0 mg/kg induced hypothermia. On the other hand, 0.05 mg/kg delta9-THC significantly reduced, whereas doses of 1.0, 2.0 and 5.0 mg/kg significantly increased the 5-HIAA levels in a dose-related manner. It is concluded that an inverse relationship exists between delta9-THC-induced changes in body temperature and alterations in brain 5-HIAA levels.
The effect of pretreatment with clomipramine hydrochloride (15 mg/kg, i.p.) on the (‐)‐trans‐A ⁹ ‐tetrahydrocannabinol (A ⁹ ‐THC)‐induced changes in body temperature and brain amines of the rat was investigated.
A dose of 0.05 mg/kg of A ⁹ ‐THC produced hyperthermia and a decrease in whole brain concentration of 5‐hydroxyindoleacetic acid (5‐HIAA). Doses of 2 and 5 mg/kg produced hypothermia and increases in brain 5‐HIAA whereas 0.5 mg/kg did not affect either parameter. A ⁹ ‐THC, at any of the doses, did not affect the whole brain concentrations of dopamine, noradrenaline or 5‐hydroxytryptamine.
Clomipramine modified these responses of A ⁹ ‐THC in that the dose‐response curves appeared to be shifted to the right.
It is concluded that clomipramine acts as an antagonist to these actions of A ⁹ ‐THC by interfering with entry of A ⁹ ‐THC into tryptaminergic neurones.
Rats were injected intravenously with 2 mg/kg (–)‐ trans ‐Δ ⁹ ‐tetrahydrocannabinol (Δ ⁹ ‐THC) at ambient temperatures of 4°, 21°, 31° and 37°C.
The general behaviour exhibited by rats treated with Δ ⁹ ‐THC was similar at all four ambient temperatures.
Body temperatures were recorded continuously before and after drug administration. At 4° and 21°C, Δ ⁹ ‐THC caused hypothermia whereas no change in body temperature occurred at 31° and 37°C.
The concentrations in the whole brain of noradrenaline (NA), dopamine, 5‐hydroxytryptamine (5‐HT) and 5‐hydroxyindoleacetic acid (5‐HIAA) were determined spectrophotofluorimetrically 1 h after drug administration. At 4°C Δ ⁹ ‐THC caused an increase of 5‐HT, at 21°C an increase of 5‐HIAA, at 31°C an increase of 5‐HIAA and a decrease of NA, and at 37°C an increase of 5‐HT and 5‐HIAA.
At all ambient temperatures, Δ ⁹ ‐THC increased the brain levels of 5‐HT and/or 5‐HIAA. A correlation between the Δ ⁹ ‐THC‐induced hypothermic response and the possible alteration of brain 5‐HT metabolism cannot be excluded.
This paper reviews the literature on the circadian rhythm of body temperature (CRT). The review starts with a brief discussion of methodological procedures followed by the description of known patterns of oscillation in body temperature, including ultradian and infradian rhythms. Special sections are devoted to issues of species differences, development and aging, and the relationships between the CRT and the circadian rhythm of locomotor activity, between the CRT and the thermoregulatory system, and between the CRT and states of disease. A section on the nervous control of the CRT is followed by summary and conclusions.
Heart rate (HR), body temperature (BT) and locomotor activity (LA) were measured continuously over 5 days in freely moving rats. In addition to the well-known circadian rhythms, all variables exhibited considerable fluctuations in amplitude mainly during the dark, but also in the light periods. The values of HR varied from 286 +/- 12 to 470 +/- 26 b.p.m. and BT from 36.15 +/- 0.15 degrees C to 38.45 +/- 0.25 degrees C. The large variability of HR, BT and LA within a single day was due more to large short-term fluctuations within periods of about 3-5 hours duration, than to differences between the light and the dark period. Good consistency of daily patterns and similarity of the 3 variables was found within the animals. Usually there were 3 or 4 regular peaks during the dark and often another peak 3-4 hours after the onset of light. Correlation coefficients, calculated on the basis of 5-min mean values, were highly significant (P less than 0.001) for LA vs HR (0.61-0.73), LA vs BT (0.40-0.53), and HR vs BT (0.61-0.68). Between-hour correlations were higher than these common correlations of 5-min values. HR vs BT (0.76-0.83) and LA vs BT (0.63-0.79) correlated as well as LA vs HR (0.72-0.83). The short-term fluctuations (within-hours) gave lower correlation coefficients for LA vs BT (0.23-0.32) and HR vs BT (0.29-0.41) than LA vs HR (0.40-0.70). This seems to result from a physiological delay of BT relative to HR and LA.
In the present study we have characterized the hypothermic effect of the psychoactive cannabinoid HU-210, by investigating its interaction with the endogenous pyrogens, IL-1 and PGE2. We also studied the involvement of the adrenergic system in mediation of this hypothermic effect. Injection of HU-210 directly into the preoptic area caused a dose dependent reduction of rectal temperature from 37 to 32.1 degrees C. Injection of the non-psychoactive analog, HU-211 which does not bind to brain cannabinoid receptor, did not affect body temperature. Injection of the adrenergic agonists, CGP-12177 and clonidine (beta, and alpha adrenergic agonists, respectively) abrogated the hypothermia induced by HU-210. Injection of the adrenergic antagonists, prazosin (alpha 1) and propranolol (beta) enhanced the hypothermic effect of HU-210. Intracerebral administration of IL-1 or PGE2 to rats pretreated with HU-210 caused a transient inhibition of the hypothermia. The ex vivo rate of basal or bacterial endotoxin-induced synthesis of PGE2 by different brain regions, including the preoptic area was not affected by HU-210 administration. These results suggest that the synthetic cannabinoid HU-210 acts in the preoptic area, probably via the brain cannabinoid receptor to induce hypothermia. The hypothermic effect can be antagonized by adrenergic agonists and enhanced by adrenergic antagonists. HU-210 does not interfere with the pyrogenic effect of IL-1 or PGE2.
Heat regulation is presented as the physiological method of handling metabolic heat, instead of temperature regulation. Experimental evidence of heat regulation from the literature is reviewed, including more than 20 years of calorimetric studies by the author. Changes in heat production are followed by slow exponential changes in heat loss, which produce changes in body heat storage. Heat balance occurs at many levels of heat production throughout the day and night, and at each level there is a related level of rectal temperature. Heat flow can be sensed by the transcutaneous temperature gradient. The controller for heat loss appears to operate like a servomechanism, with feedback from heat loss and possibly feedforward from heat production. Physiological responses defend the body heat content, but heat content varies over a range that is related to heat load. Changes in body heat content drive deep body temperatures.
Anandamide (arachidonylethanolamide) is a brain constituent which binds to the cannabinoid receptor. We now report the first in vivo examination of this ligand. Anandamide administered i.p. in mice, caused lowering of activity in an immobility and in an open field test, and produced hypothermia and analgesia. These effects parallel those caused by psychotropic cannabinoids.
The purpose of this study was to elucidate brain areas that mediate cannabinoid-induced antinociception as assessed in the tail-flick test. Intracerebroventricular administration of the prototypical cannabinoid, delta 9-tetrahydrocannabinol, and the potent bicyclic analog, CP-55,940, produced antinociception at ED50 values of 373 and 64 nmol/rat, respectively. Hypothermic and cataleptic effects also were observed after i.c.v. administration of CP-55,940, but not delta 9-tetrahydrocannabinol. In contrast, the endogenous cannabinoid, anandamide, failed to elicit any apparent pharmacological effects. Administration of CP-55,940 into the caudate putamen produced catalepsy, but failed to produce either antinociception or hypothermia. Micro-injection of CP-55,940 into the ventrolateral aspect of the periaqueductal gray (PAG), in the region of the dorsal raphe, produced antinociception (ED50 dose = 28 nmol/rat), catalepsy and hypothermia. CP-56,667, the inactive stereoisomer of CP-55,940, failed to produce any effects when injected into the same site. Additional studies demonstrated that pertussis toxin completely prevented the pharmacological effects of CP-55,940 when both agents were administered into the posterior ventrolateral PAG. In contrast, dibutyryl-cAMP failed to attenuate cannabinoid-induced antinociception. Finally, CP-55,940 administered into either the posterior dorsolateral or the anterior ventrolateral areas of the PAG was without effect. These results indicate that the antinociceptive and cataleptic effects of cannabinoids in the PAG are dose-related, exhibit regional specificity and are enantioselective. Moreover, the complete prevention of these pharmacological effects by pertussis toxin pretreatment in the PAG is consistent with the involvement of G proteins. These findings suggest that the posterior ventrolateral PAG may be an important brain area for the antinociceptive and cataleptic effects of the cannabinoids.
Immunohistochemical distribution of cannabinoid receptors in the adult rat brain was studied using specific purified antibodies against the amino-terminus of the CB1 receptor. Our results generally agree well with the previous studies using CB1 receptor autoradiography and messenger RNA in situ hybridization. However, because of its greater resolution, immunohistochemistry allowed identification of particular neuronal cells and fibers that possess cannabinoid receptors. CB1-like immunoreactivity was found in axons, cell bodies and dendrites, where it appeared as puncta in somata and processes. Both intensely and moderately or lightly stained neurons were observed. The intensely stained neurons were dispersed and only occur in cortical structures including hippocampal formation and olfactory bulb. Moderately or lightly stained neurons were found in caudate–putamen and amygdala. In the hippocampal formation only intensely stained neurons were observed. The cell bodies of pyramidal neurons in CA1 and CA3 fields appeared to be unstained but surrounded by a dense plexus of immunoreactive fibers. The granule cells in the dentate area were also immunonegative. Many intensely stained neurons were located at the base of the granule cell layer. CB1-like immunoreactive neurons and fibers were also found in the somatosensory, cingulate, perirhinal, entorhinal and piriform cortices, in claustrum, amygdaloid nuclei, nucleus accumbens and septum. Beaded immunoreactive fibers were detected in periaqueductal gray, nucleus tractus solitarius, spinal trigeminal tract and nucleus, dorsal horn and lamina X of the spinal cord. A triangular cap-like mass of immunoreactivity was found to surround the basal part of the Purkinje cell body in the cerebellum. Only small, lightly stained cells were found in the molecular layer in the cerebellum close to the Purkinje cell layer.
We employed the CB1 cannabinoid receptor antagonist SR 141716A (3 mg/kg, i.p.) to investigate whether behavioural effects induced in rats by anandamide, an endogenous cannabinoid (20 mg/kg, i.p.), were mediated by the cannabinoid CB1 receptor. Anandamide reduced ambulatory (67%) and non-ambulatory activities (rearing and grooming, 84% and 90% respectively), with a strong cataleptic effect, produced hypothermia (about -1 degree C) and hindlimb splaying, and reduced defecation (79%). It did not significantly increase either the tail-flick or hot-plate latencies. Except for the decreased defecation, these responses were all blocked by SR 141716A. Although only single doses of the agonist and antagonist were used, the findings indicate that these behavioural effects are probably mediated by an interaction with cannabinoid CB1 receptors.
The present study investigated the effect of the selective cannabinoid agonist, WIN 55212-2 [(4,5-dihydro-2-methyl-4(4-morpholinylmethyl)-1-(1-naphthalenyl-carbonyl)-6H-pyrrolo[3,2,1ij]quinolin-6-one], on body temperature. WIN 55212-2 (1, 2.5, 5, and 10 mg/kg, i.m.) induced hypothermia in a dose-dependent manner. The peak hypothermia occurred 60 to 180 min postinjection. Body temperature was still suppressed 5 h after the injection of the highest dose of WIN 55212-2. The selective CB(1) antagonist, SR141716A [N-(piperidin-1-yl)-5-(4-chlorophenyl)-1-(2,4-dichlorophenyl)-4-methyl-1H-pyrazole-3-carboxamide hydrochloride] (5 and 10 mg/kg, i.m.), blocked the WIN 55212-2-induced hypothermia, suggesting that CB(1) receptor activation mediated the hypothermia. In contrast, the selective CB(2) antagonist, SR144528 [N-((1S)-endo-1,3,3-trimethyl bicyclo heptan-2-yl]-5-(4-chloro-3-methylphenyl)-1-(4-methylbenzyl)-pyrazole-3-carboxamide)] (5 mg/kg, i.m.), did not alter the WIN 55212-2-induced hypothermia. Neither SR141716A nor SR144528 alone altered body temperature. WIN 55212-2 (1-30 microg/microl) injected directly into the preoptic anterior hypothalamic nucleus (POAH) induced hypothermia in an immediate and dose-dependent fashion. The hypothermia produced by intra-POAH injection of WIN 55212-2 was brief, with body temperature returning to baseline 60 min postinjection. SR141716A (5 mg/kg, i.m.) abolished the hypothermia induced by intra-POAH injection of WIN 55212-2 (30 microg/microl), indicating that CB(1) receptors in the POAH mediated the hypothermia. The present results confirm the idea that CB(1) receptors mediate the hypothermic response to cannabinoid agonists. Moreover, the present data suggest that 1) the POAH is the central locus for thermoregulation, and 2) CB(1) receptors within the POAH are the primary mediators of cannabinoid-induced hypothermia.
The central cannabinoid receptor (CB(1)) antagonist, SR-141716A, has been used extensively to ascertain that cannabinoids interact with the CB(1) receptor. SR-141716A has been shown to produce effects opposite of cannabinoids when administered alone. It has been theorized that SR-141716A may act as an inverse agonist at the CB(1) receptor or by disinhibiting an endogenous cannabinoid tone. In an effort to ascertain the exact interaction between SR-141716A and the CB(1) receptor, we have conducted a structure-activity relationship study to compare CB(1) receptor affinity of SR-141716A analogs with their ability to produce an increase in locomotor activity. SR-141716A produced a significant increase in locomotor activity in mice within the first hour of administration. Twenty SR-141716A analogs from five different chemical series were also tested. Our data implicate particular regions of the SR-141716A molecule that may be involved in stimulation and depression of locomotor activity. When the K(I) of the analogs was plotted against the percent stimulation that each analog produced, it is evident that there is no correlation between the ability of the analogs to stimulate locomotor activity and their affinity for the CB(1) receptor. [35S]GTPgammaS binding data indicate that SR-141716A and five of the analogs are inverse agonists. However, none of the analogs demonstrating inverse agonism produce stimulation of locomotor activity. It is therefore concluded that the SR-141716A-induced stimulation in locomotor activity is not the result of inverse agonist activity at the CB(1) receptor or by disinhibition of an endogenous tone.
Cannabinoid receptors were named because they have affinity for the agonist delta9-tetrahydrocannabinol (delta9-THC), a ligand found in organic extracts from Cannabis sativa. The two types of cannabinoid receptors, CB1 and CB2. are G protein coupled receptors that are coupled through the Gi/o family of proteins to signal transduction mechanisms that include inhibition of adenylyl cyclase, activation of mitogen-activated protein kinase, regulation of calcium and potassium channels (CB1 only), and other signal transduction pathways. A class of the eicosanoid ligands are relevant to lipid-mediated cellular signaling because they serve as endogenous agonists for cannabinoid receptors, and are thus referred to as endocannabinoids. Those compounds identified to date include the eicosanoids arachidonoylethanolamide (anandamide), 2-arachidonoylglycerol and 2-arachidonylglyceryl ether (noladin ether). Several excellent reviews on endocannabinoids and their synthesis, metabolism and function have appeared in recent years. This paper will describe the biological activities, pharmacology, and signal transduction mechanisms for the cannabinoid receptors, with particular emphasis on the responses to the eicosanoid ligands.
After the discovery, in the early 1990s, of specific G-protein-coupled receptors for marijuana's psychoactive principle Δ9-tetrahydrocannabinol, the cannabinoid receptors, and of their endogenous agonists, the endocannabinoids, a decade of investigations has greatly enlarged our understanding of this altogether new signalling system. Yet, while the finding of the endocannabinoids resulted in a new effort to reveal the mechanisms regulating their levels in the brain and peripheral organs under physiological and pathological conditions, more endogenous substances with a similar action, and more molecular targets for the previously discovered endogenous ligands, anandamide and 2-arachidonoylglycerol, or for some of their metabolites, were being proposed. As the scenario becomes subsequently more complicated, and the experimental tasks to be accomplished correspondingly more numerous, we briefly review in this article the latest ‘additions’ to the endocannabinoid system together with earlier breakthroughs that have contributed to our present knowledge of the biochemistry and pharmacology of the endocannabinoids.
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