Activation of peripheral serotonin2 receptors induces hypothermia in mice

5-HT2A receptors are involved in the pharmaco-toxicological effects of the synthetic cannabinoids JWH-018 and 5F-PB22: In vivo studies in mice

Over the last years, Synthetic Cannabinoids (SCs) have been among the largest and most frequently seized groups of Novel Psychoactive Substances (NPS). These substances have been frequently detected in biological samples from patients involved in several intoxication and death cases. Their serious adverse effects have been related to their action as potent agonist of cannabinoid CB1 receptors. However, evidence concerning the potential interaction between SCs and serotoninergic mechanisms has emerged. Therefore, this study aims to evaluate the involvement of 5-HT2A receptors in the effects induced by acute systemic administration of 1-pentyl-3-(1-naphthoyl)indole (JWH-018; 1 mg/kg) and quinolin-8-yl 1-pentyfluoro-1H-indole-3-8-carboxylate (5F-PB22; 1 mg/kg). Sensorimotor (visual, acoustic, and tactile) responses, pain threshold (acute mechanical and thermal nociception), core temperature, breath rate and motor performance (stepping activity) have been assessed in CD-1 male mice. The present results pointed out that both substances deeply alter sensorimotor responses, nociceptive threshold, core temperature, breath rate and motor activity in mice. Noteworthy, pretreatment with the selective 5-HT2A receptors antagonist MDL100907 (0.1 mg/kg) at least partially prevented sensorimotor disruption, antinociception and hypothermic effects. Conversely, the respiratory and motor impairment was not prevented. Thus, it states the relevance of serotoninergic 5-HT2A mechanisms on pharmaco-toxicological effects induced by SCs.

5-HT Receptors and Temperature Homeostasis

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

International Union of Basic and Clinical Pharmacology. CX. Classification of Receptors for 5-hydroxytryptamine; Pharmacology and Function

5-HT receptors expressed throughout the human body are targets for established therapeutics and various drugs in development. Their diversity of structure and function reflects the important role 5-HT receptors play in physiologic and pathophysiological processes. The present review offers a framework for the official receptor nomenclature and a detailed understanding of each of the 14 5-HT receptor subtypes, their roles in the systems of the body, and, where appropriate, the (potential) utility of therapeutics targeting these receptors. SIGNIFICANCE STATEMENT: This review provides a comprehensive account of the classification and function of 5-hydroxytryptamine receptors, including how they are targeted for therapeutic benefit.

Serotonin is involved in the psychostimulant and hypothermic effect of 4-methylamphetamine in rats

4-Methylamphetamine (4-MA) has recently emerged as a designer drug of abuse in Europe and it is consumed always with amphetamine. There have been reported some deaths and non-fatal intoxications related to 4-MA. We investigated the changes in locomotor activity and body temperature after 4-MA administration to male Sprague-Dawley rats. Our experiments were carried out at a normal or high ambient temperature. 4-MA (2.5-10mg/Kg, given subcutaneously) increased, in a dose-dependent manner, the horizontal locomotor activity that was significantly reduced by ketanserin, p-cholorophenylalanine (pCPA) or haloperidol, but not by pindolol. In addition, we have studied the effect of 4-MA on core body temperature by means of an implanted electronic thermograph, enabling continuous measurement of body temperature. We observed a dose-dependent hypothermic response to 4-MA that reached a maximum 45 min after a single injection. We also evidenced slight tachyphylaxis to the hypothermic effect when 4-MA was administered four times in a 2h interval. The pre-treatment of animals with pCPA or pindolol, but not with ketanserin, fully abolished the hypothermic effect of 4-MA. With all that, we conclude that hypothermia induced by 4-MA is due to the release of 5-HT which activates postsynaptic 5-HT1A receptors.

Animal models of the serotonin syndrome: a systematic review

The serotonin syndrome (SS) is a potentially life-threatening disorder in humans which is induced by ingestion of an overdose or by combination of two or more serotonin (5-HT)-enhancing drugs. In animals, acute administration of direct and indirect 5-HT agonists also leads to a set of behavioral and autonomic responses. In the current review, we provide an overview of the existing versions of the animal model of the SS. With a focus on studies in rats and mice, we analyze the frequency of behavioral and autonomic responses following administration of 5-HT-enhancing drugs and direct 5-HT agonists administered alone or in combination, and we briefly discuss the receptor mediation of these responses. Considering species differences, we identify a distinct set of behavioral and autonomic responses that are consistently observed following administration of direct and indirect 5-HT agonists. Finally, we discuss the importance of a standardized assessment of SS responses in rodents and the utility of animal models of the SS in translational studies, and provide suggestions for future research.

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

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

8-OH-DPAT acts on both 5-HT1A and 5-HT7 receptors to induce hypothermia in rodents

Studies using selective drugs and knockout mice have demonstrated that the 5-HT(7) receptor plays an instrumental role in serotonin-induced hypothermia. There is also evidence supporting an involvement of the 5-HT(1A) receptor, although mainly from studies using 8-hydroxy-2(di-n-propylamino)tetralin (8-OH-DPAT), a 5-HT(1A/7) receptor agonist. Here we studied the effects of 8-OH-DPAT and selective antagonists for the 5-HT(1A) and 5-HT(7) receptors on body temperature in rats, wild-type (5-HT(7)(+/+)) mice and knockout (5-HT(7)(-/-)) mice. At lower doses (0.3-0.6 mg/kg, i.p.), 8-OH-DPAT decreased body temperature in 5-HT(7)(+/+) mice but not in 5-HT(7)(-/-) mice. At a higher dose (1 mg/kg, i.p.) 8-OH-DPAT induced hypothermia in both 5-HT(7)(-/-) and 5-HT(7)(+/+) mice. The 5-HT(1A) receptor antagonist (S)-N-tert-butyl-3-(4-(2-methoxyphenyl)piperazine-1-yl)-2-phenylpropanamide (WAY-100135) (10 mg/kg, i.p.) inhibited the effect of 8-OH-DPAT at all doses in rats and mice. In 5-HT(7)(+/+) mice the selective 5-HT(7) receptor antagonist (R)-3-(2-(2-(4-methylpiperidin-1-yl)-ethyl)pyrrolidine-1-sulfonyl)phenol (SB-269970) (10 mg/kg, i.p.) fully inhibited the hypothermia induced by 0.3 mg/kg 8-OH-DPAT, but not that of higher doses. In rats, SB-269970 caused a 60% inhibition of the hypothermia induced by 0.3 mg/kg 8-OH-DPAT. Thus, both 5-HT(7) and 5-HT(1A) receptors are involved in a complex manner in thermoregulation, with the 5-HT(7) receptor being more important at lower, possibly more physiological, concentrations.

No hypothermic response to serotonin in 5-HT7 receptor knockout mice

With data from recently available selective antagonists for the 5-HT(7) receptor, it has been hypothesized that 5-hydroxytryptamine (5-HT)-induced hypothermia is mediated by the 5-HT(7) receptor, an effect previously attributed to other receptor subtypes. It has been established that the biologically active lipid oleamide allosterically interacts with the 5-HT(7) receptor to regulate its transmission. The most well characterized effects of oleamide administration are induction of sleep and hypothermia. Here, we demonstrate, by using mice lacking the 5-HT(7) receptor, that 5-HT-induced hypothermia is mediated by the 5-HT(7) receptor. Both 5-HT and 5-carboxamidotryptamine, a 5-HT(1) and 5-HT(7) receptor agonist, in physiological doses fail to induce hypothermia in 5-HT(7) knockout mice. In contrast, oleamide was equally effective in inducing hypothermia in mice lacking the 5-HT(7) receptors as in wild-type mice. When administered together, 5-HT and oleamide showed additive or greater than additive effects in reducing body temperature. Taken together, the results show that 5-HT-induced hypothermia is mediated by the 5-HT(7) receptor, and that oleamide may act through an independent mechanism as well as at an allosteric 5-HT(7) receptor site to regulate body temperature.

Decrease of core body temperature in mice by dehydroepiandrosterone

Dietary dehydroepiandrosterone (DHEA) reduces food intake in mice, and this response is under genetic control. Moreover, both food restriction and DHEA can prevent or ameliorate certain diseases and mediate other biological effects. Mice fed DHEA (0.45% w/w of food) and mice pair-fed to these mice (food restricted) for 8 weeks were tested for changes in body temperature. DHEA was more efficient than food restriction alone in causing hypothermia. DHEA injected intraperitoneally also induced hypothermia that reached a nadir at 1 to 2 hr, and slowly recovered by 20 to 24 hr. This effect was dose dependent (0.5-50 mg). Each mouse strain tested (four) was susceptible to this effect, suggesting that the genetics differ for induction of hypophagia and induction of hypothermia. Because serotonin and dopamine can regulate (decrease) body temperature, we treated mice with haloperidol (dopamine receptor antagonist), 5,7-dihydroxytryptamine (serotonin production inhibitor), or ritanserin (serotonin receptor antagonist) prior to injection of DHEA. All of these agents increased rather than decreased the hypothermic effects of DHEA. DHEA metabolites that are proximate (5-androstene-3beta, 17beta-diol and androstenedione) or further downstream (estradiol-17beta) were much less effective than DHEA in inducing hypothermia. However, the DHEA analog, 16alpha-chloroepiandrosterone, was as active as DHEA. Thus, DHEA administered parentally seems to act directly on temperature-regulating sites in the body. These results suggest that DHEA induces hypothermia independent of its ability to cause food restriction, to affect serotonin or dopamine functions, or to act via its downstream steroid metabolites.

Involvement of the 5-HT(2) receptor in hyperthermia induced by p-chloroamphetamine, a serotonin-releasing drug in mice

The effects of a serotonin (5-hydroxytryptamine, 5-HT)-releasing drug, p-chloroamphetamine (PCA), on body temperature were investigated in mice. PCA induced hyperthermia in mice. PCA-induced hyperthermia was inhibited by the 5-HT(2A/2B/2C) receptor antagonist, 4-isopropyl-7-methyl-9-(2-hydroxy-1-methyl-propoxycarbonyl)-4,6A,7 , 8,9,10,10A-octahydro-indolo[4,3-FG]quinolone maleate (LY53857). The 5-HT(2A) receptor antagonist, ketanserin, reduced the PCA-induced hyperthermia, while the 5-HT(2B/2C) receptor antagonist, N-3-pyridinyl-3,5-dihydro-5-methyl-benzo[1,2-b:4, 5-b']dipyrrole-1(2H)-carboxamide (SB 206553), enhanced it. LY 53857, ketanserin and SB 206553 did not affect hyperactivity in mice treated with PCA. These results suggest that PCA-induced hyperthermia in mice is mediated by 5-HT(2A) receptors and is not related to changes in locomotor activity.

Evidence that 5-HT2A receptors are not involved in 5-HT-mediated thermoregulation in mice

To determine the role of 5-hydroxytryptamine2A (5-HT2A) receptors in 5-HT-mediated thermoregulation in mice, we studied the effects of a 5-HT2A receptor agonist and 5-HT2A receptor antagonists on the body temperature, and the effects of selective 5-HT2A receptor and nonselective 5-HT receptor antagonists on hypothermia induced by 5-hydroxytryptophan (5-HTP). (+/-)-1-(2,5-Dimethoxy-4-iodophenyl)-2-aminopropane (DOI), a 5-HT2A receptor agonist, did not change body temperature in mice at doses of 1 and 5 mg/kg, intraperitoneally (IP), which induced head twitch response. Three 5-HT2A receptor antagonists, ketanserin (1 mg/kg, orally), ritanserin (1 and 10 mg/kg, orally), and DV-7028 (10 mg/kg, orally), also failed to alter body temperature, although these three 5-HT2A receptor antagonists at > or = 1 mg/kg, orally, inhibited head twitch response induced by 5-HTP (200 mg/kg, IP), a precursor of 5-HT. Ketanserin (1 mg/kg, orally), ritanserin (1 and 10 mg/kg, orally), and DV-7028 (10 mg/kg, orally) did not inhibit hypothermia induced by 5-HTP (200 mg/kg, IP). A nonselective 5-HT receptor antagonist, methysergide (1 mg/kg, subcutaneously), attenuated hypothermic response to 5-HTP. These results suggest that in mice, 5-HT2A receptors are unlikely to be involved in 5-HT-mediated thermoregulation.

The involvement of the peripheral 5-HT2A receptor in peripherally administered serotonin-induced hyperglycemia in rats

The mechanism of the hyperglycemic response to intraperitoneally administered serotonin (5-HT) was studied in rats. 5-HT i.p.-induced hyperglycemia was strongly antagonized by the 5-HT2A receptor antagonist ketanserin. 5-HT did not affect the serum insulin levels and increased plasma glucagon levels only at the high dose of 10 mg/kg. 5-HT dose-dependently induced a remarkable increase in plasma adrenaline levels and these effects were antagonized by ketanserin. 5-HT-induced hyperglycemia was abolished by adrenodemedullation. These results suggest that the hyperglycemic effects of 5-HT are closely related to the release of adrenaline from the adrenal gland, mediated by 5-HT2A receptors.

Alterations of in-vitro 5-HT receptor pharmacology as a function of multiple treatment with 5-hydroxytryptamine or 8-hydroxy-2-(di-N-propylamino) tetralin in rat isolated aorta, uterus and fundus, and guinea-pig isolated trachea

The effects of single and multiple (5, 10, or 15 days) administration of the 5-HT1A agonist 8-hydroxy-2-(di-N-propylamino) tetralin (8-OH-DPAT) (3 mg kg-1, i.p.) or 5-HT (3 mg kg-1, i.p.) in-vivo on the response of selected isolated smooth muscles to 5-HT in-vitro were investigated. Single dosing with 8-OH-DPAT did not alter the responses of the isolated tissues (rat aorta, uterus or fundus, or guinea-pig trachea) to 5-HT, while multiple dosing with 8-OH-DPAT produced rightward shifts and a suppression of the maximum response of all these tissues to 5-HT, with the exception of the rat stomach fundus. Multiple administration of 5-HT had no effect on the in-vitro response of the tissues to 5-HT. These data indicate that multiple administration of 8-OH-DPAT desensitizes or down-regulates the peripheral 5-HT2 receptors found on the rat aorta and uterus, and guinea-pig trachea.

Hypothermia induced by hyperbaric oxygen is not blocked by serotonin antagonists

Exposure to HBO causes hypothermia, bradycardia, head weaving, resting tremor, piloerection, and straub tail in rats. These physiological and behavioral responses can also be evoked by selective activation of serotonin1A (5-HT1A) receptors. The purpose of the current study was to determine if hypothermia caused by HBO is due to increased activation of 5-HT1A receptors. The levels of brain biogenic amines were measured in brain regions of Sprague-Dawley (SD) rats exposed to HBO. Exposure to HBO caused an increase in the levels of 5-hydroxyindoleacetic acid (5-HIAA) in the striatum (92%, p < 0.05) and occipital-temporal cortex (116%, p < 0.05), but not in other brain regions. Exposure to HBO did not change the levels of tryptophan, serotonin (5-HT), other biogenic amines, or their metabolites. It is hypothesized that the Fawn Hood (FH) rat, which is reported to be resistant to hypothermia induced by 8-hydroxy-2-(di-n-propylamino)tetralin (8-OH-DPAT), has an abnormality of 5-HT1A receptor activity. Although the FH rat was more resistant to hypothermia induced by HBO than the SD rat, we were not able to confirm that this rat was resistant to hypothermia induced by 8-OH-DPAT. The 5-HT receptor antagonists, 1-(1H-Indol-4-yloxy)-3-[(1-methylethyl)amino]-2-propanol (Pindolol), 1-(2-methoxyphenyl)-4-[4-(2-phthalimido)butyl] piperazine hydrobromide (NAN-190), and methysergide, did not block hypothermia induced by HBO in SD rats. A series of control experiments were used to confirm that the antagonists blocked hypothermia induced by serotonin agonists.(ABSTRACT TRUNCATED AT 250 WORDS)

Peripherally administered serotonin induces hyperglucagonemia in mice

Peripherally administered serotonin (5-HT) induced a marked increase in the plasma glucagon level in mice. The hyperglucagonemic effects of 5-HT were completely antagonized by methysergide, ketanserin and ritanserin which have a high affinity for 5-HT2 receptors. However, the 5-HT3 receptor antagonist ICS 205-930 and MDL 72222 were without effect. These findings suggest that the activation of the peripheral 5-HT2 receptor induces the increase in plasma glucagon level and that these receptors may play a role in the release of glucagon.

Effect of the serotonin agonist, MK-212, on body temperature in schizophrenia

The effects of 6-chloro-2-(1-piperaziny)pyrazine (MK-212), a centrally acting 5-HT1C/5-HT2 agonist, on body temperature and behavior were assessed using a single-blind cross-over design in 23 schizophrenic patients and 22 normal controls. Body temperature was assessed before drug administration and at 30-min intervals for 3 hr. Each subject was administered placebo or MK-212. MK-212 significantly elevated temperature in normal controls. There was no overall MK-212-induced increase in temperature compared to placebo in the schizophrenic patients; however, 13 of 23 (56.5%) patients had a larger increase in temperature after MK-212 than placebo, 3 of 23 (13.1%) had no change, whereas the temperature change after placebo was greater than after MK-212 in 7 of 23 (30.4%) patients. MK-212 produced significant increases in nausea, feeling strange, and arousal but these effects did not differ between groups. These results are consistent with decreased 5-HT2 receptor responsivity in some patients with schizophrenia.

Inhibition of methionine incorporation into brain proteins after the systemic administration of p-chlorophenylalanine and L-5-hydroxytryptophan

The effects of p-chlorophenylalanine (p-CPA) and L-5-hydroxytryptophan (L-5-HTP) on local rates of plasma methionine incorporation into brain proteins were investigated by a quantitative autoradiographic method. The sequential i.v. administration of p-CPA (280 mg/kg, 42 h before the measurement) and L-5-HTP (60 mg/kg, 40 min before the measurement) resulted in an average 82% decrease of plasma methionine incorporation. The two treatments given separately also reduced the rates of plasma methionine incorporation in all the brain areas examined by 33 and 50%, respectively for p-CPA and L-5-HTP. These results indicate that: (1) p-CPA and L-5-HTP, two drugs which affect brain serotonin production in opposite ways, both produce large and general decreases of brain protein synthesis; (2) the administration of L-5-HTP does not restore the p-CPA-induced inhibition of brain protein synthesis but induces further decreases of protein synthesis. These results suggest that the reduction of brain protein synthesis in p-CPA-treated rats is mainly related to high circulating levels of p-CPA and phenylalanine; and that brain serotonin is not the only factor involved in the widespread metabolic changes observed. Such profound alterations of brain metabolism should be considered when interpreting the behavioral and neurochemical effects of p-CPA and L-5-HTP.