Serotonin and its metabolites: their respective roles in the production of hypothermia in the mouse

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.

Both hydroxy- and methoxyindoles modify basal temperature in the rat

The various pineal gland tryptophan metabolites were administered to male rats intraperitoneally (100 micrograms/kg) and rectal temperatures were recorded. Of the compounds tested, hydroxytryptophan, N-acetylserotonin, hydroxytryptophol, and their corresponding methoxyindoles all caused a marked hypothermia, indicating that several indolic products may be involved in thermoregulation. Although the brain penetration of indoles is poor, a central site of action would be most likely, although peripheral actions cannot be excluded. The mechanism of induction of hypothermia may involve peptides, the pituitary-thyroid axis, the adrenal gland, or a combination of these. These results may suggest that the pineal gland integrates environmental cues to act in concert with physiological thermostats in the fine tuning of thermoregulation.

Determination of endogeneous indoleacetic acid and tryptophol in mouse brain by high performance liquid chromatography with fluorometric detection

A simple and sensitive method using high performance liquid chromatography with fluorometric detection has been developed for the identification and quantitation of the endogeneous tryptamine metabolites, indoleacetic acid (IAA) and tryptophol (TOL) in the normal mouse brain. The limits of sensitivity are 5pg for both IAA and TOL. The extract procedure from the brain is only to deproteinize samples. The mean concentrations of IAA and TOL in the mouse brain are 8.99 +/- 0.31 ng/g and 3.56 +/- 0.21 ng/g respectively. The effects of pargyline and tryptamine on the levels of IAA and TOL were also studied.

Simultaneous determination of tryptophan and its metabolites in mouse brain by high-performance liquid chromatography with fluorometric detection

A new method for the determination of tryptophan and its metabolites in a single mouse brain using high-performance liquid chromatography (HPLC) with fluorometric detection is described. Tryptophan, serotonin, 5-hydroxyindoleacetic acid, indoleacetic acid, and tryptophol were clearly separated by a C8 reverse-phase column. Tissue preparation is performed only to centrifuge homogenates of brain prior to the injection to HPLC. The sensitivity is in the range from 10 to 15 pg.

Effects of ethanol on thermoregulation

Clinical reports of accidental hypothermia in alcohol intoxicated individuals exposed to low ambient temperature ( Paton , 1983) have generally been borne out by experimental studies in healthy volunteers. Small doses of ethanol, given to human subjects at normal ambient temperature (Ta), have very little effect on body temperature but a combination of large dose, low Ta and vasodilatation provoked by strenuous exercise, causes a sharp fall in rectal temperature. In experimental animals, the use of relatively larger doses of alcohol and more extreme temperatures, both above and below the thermoneutral zone, has shown that the effect of ethanol is essentially poikilothermic, i.e. an impairment of adaptation to both heat and cold. This effect has been studied in greater detail, in relation to each of the basic thermoregulatory processes. Though small doses of alcohol may increase the metabolic rate under some circumstances, the most common effect at low Ta is inhibition of shivering and therefore reduction of thermogenesis. At the same time it tends to cause increased heat loss by cutaneous vasodilatation. This makes for a greater feeling of comfort in the cold exposed subjects but increases in rate of fall of core temperature. The combination of decreased thermogenesis and increased heat loss, despite falling body temperature, is suggestive of a lowering of the set-point of the thermoregulatory control mechanisms. Consistent with this is a slight increase in ventilatory heat loss after low doses of ethanol but larger doses cause respiratory depression, so that heat loss through the lungs is minor. However, at high Ta ethanol caused hyperthermia in experimental animals and shows enhanced lethality, so that impairment of thermoregulatory effector mechanisms seems to be at least as important as change in set-point. Studies of the effects of ethanol on electrophysiological activity of single neurons in the pre-optic area and anterior hypothalamus (POAH), biochemical activities of neuronal membranes, hypothalamic blood flow, conventional neurotransmitters, amino acid putative neurotransmitters, neuropeptides, prostaglandins and inorganic ions have all failed so far to yield a clear comprehensive picture of the mechanisms by which ethanol affects thermoregulation. In each case, contradictory evidence has been obtained concerning the consequences of ethanol administration, whether by oral, intraperitoneal, intravenous, intracerebroventricular, or direct local (POAH) route.(ABSTRACT TRUNCATED AT 400 WORDS)

Effects of aldehyde dehydrogenase inhibitors on enzymes involved in the metabolism of biogenic aldehydes in rat liver and brain

The effects of the aldehyde dehydrogenase inhibitors disulfiram, coprine and cyanamide on enzymes involved in the metabolism of biogenic aldehydes in rat liver and brain were studied. Both liver and brain aldehyde dehydrogenase activities were significantly decreased in rats pretreated with these drugs. In the liver, the low-Km aldehyde dehydrogenase activity was markedly decreased by all three drugs after 2 and 24 hr whereas only cyanamide inhibited the high-Km enzymes. The brain ALDH-activity with a low acetaldehyde concentration was significantly decreased by coprine and cyanamide at both times tested, whereas disulfiram caused no change after 2 hr but an inhibition of 38% after 24 hr. The brain ALDH-activity with a high acetaldehyde concentration was significantly decreased by coprine and cyanamide but not by disulfiram. The activity of the substrate specific enzyme succinate semialdehyde dehydrogenase in brain was slightly but significantly decreased in rats pretreated with cyanamide but not in rats pretreated with disulfiram or coprine. None of the drugs caused any changes in the activities of aldehyde reductase and monoamine oxidase in brains in vivo. The activity of monoamine oxidase in liver was significantly decreased by coprine after 24 hr. In contrast to the effects obtained in vivo, disulfiram was found to be an inhibitor in vitro of brain succinate semialdehyde dehydrogenase and liver monoamine oxidase. Aldehyde reductase was slightly inhibited by both disulfiram and 1-aminocyclopropanol in vitro.

5-hydroxytryptophol in the cerebrospinal fluid and urine of alcoholics and healthy subjects

The serotonin metabolite 5-hydroxytryptophol was determined in cerebrospinal fluid and urine of alcoholics and healthy subjects, by a glass capillary gas chromatographic-mass spectrometric method. The urinary excretion rate (14.6 +/- 2.9 pmoles/mumoles creatinine) and urine (109 +/- 20 pmoles/ml) and cerebrospinal fluid (4.12 +/- 0.21 pmoles/ml) concentrations in healthy subjects were established. Only 1% of the 5-hydroxytryptophol in urine occurred in free form. Ethanol ingestion (80, 120 g) by healthy subjects lead to a 20--100-fold increase in the urinary excretion rate of 5-hydroxytryptophol. In cerebrospinal fluid the increase was about 60%. Alcoholics had increased urinary excretion rates and cerebrospinal fluid levels during intoxication, which were in the same range as in intoxicated healthy subjects. During recovery from intoxication, the 5-hydroxytryptophol level in alcoholics decreased, but the CSF levels were still higher than in healthy subjects.

Concentration of serotonin metabolites in the cerebrospinal fluid from alcoholics before and during disulfiram therapy

The levels of 5-hydroxytryptophol and 5-hydroxyindoleacetic acid were measured in the cerebrospinal fluid before and after one week of disulfiram treatment (400 mg/day) from ten male hospitalized alcoholic patients. The disulfiram treatment induced elevated (P less than 0.001) levels of 5-hydroxytryptophol. The levels were higher than in a control group, both before (P less than 0.01) and after (P less than 0.001) the treatment. No effects on the levels of 5-hydroxyindoleacetic acid were noted. The results indicate an altered serotonin metabolism in alcoholics, which is further potentiated by disulfiram treatment.

Changes in body temperature after administration of adrenergic and serotonergic agents and related drugs including antidepressants

This survey, the third in a series, presents extensive tabulations of literature, primarily since 1965, on thermoregulatory effects of adrenergic and serotonergic agonists and their antagonists including ergot alkaloids, amphetamines, tryptamines, monoamine oxidase inhibitors, tricyclic and other antidepressants, a variety of other agents which alter presynaptic aminergic mechanisms including reserpine, 6-hydroxydopamine, p-chlorophenylalanine, alpha-methyltyrosines, cocaine, guanethidine and bretylium. The information listed includes the species used, route of administration and dose of drug, the environmental temperature at which the experiments were performed, the number of tests, the direction and magnitude of body temperature change and remarks on the presence of special conditions, such as age or lesions, or on the influence of other drugs, such as antagonists, on the response to the primary drug.

Hypothermia induced in mice by enzyme-mediated depletion of serotonin

Injection of a purified serotonin (and tryptophan)-degrading enzyme into mice produced a pronounced hypothermia when the mice were maintained at 22 degrees C, but not at 30 degrees C. Brain levels of serotonin and tryptophan were strikingly depleted, but concentrations of norepinephrine and dopamine remained unchanged.

The mechanism of action of delta 9-tetrahydrocannabinol on body temperature in mice

The effect of delta 9-tetrahydrocannabinol (delta 9-THC) on body temperature of the mouse was studied. A dose-response relationship (5-100 mg/kg) for the hypothermic effect of delta 9-THC was seen. The investigation as to the mechanism underlying the hypothermic action of delta 9-THC was also investigated. The relatively specific dopamine antagonist haloperidol potentiated delta 9-THC-induced hypothermia as did the alpha-adrenoceptor antagonist phenoxybenzamine. However, depletion of serotonin with P-chlorophenylalanine reduced the hypothermic response to delta 9-THC as did pretreatment with the serotonin antagonist methysergide. Inhibition of re-uptake of serotonin with clomipramine potentiated the hypothermia following delta 9-THC. It is suggested that the hypothermic effect of delta 9-THC in the mouse is mediated to a large extent via serotonergic mechanisms.

Changes in body temperature after administration of amino acids, peptides, dopamine, neuroleptics and related agents

Drugs may alter body temperature by acting on any component of the thermoregulatory system. These components include heat production, heat conservation and heat loss effectors and their efferent pathways, thermosensors and their afferent pathways and neurons within the central nervous system that coordinate thermoregulatory effector activities. A thermostat is often thought to be involved although thermoregulation can be explained by models that do not incorporate a thermostat. An action on a particular component can be assessed by determining the effect of a drug on body temperature over a range of environmental temperatures and by observation and measurement of associated changes in effector activities. A scheme for such assessment is presented along with examples of its use. The study of drug-induced changes in body temperature has expanded greatly within the past decade. The primary purpose of this review is to provide a readily available source of information on interactions between certain drugs and the thermoregulatory system. Extensive tables are presented of body temperature changes after administration of amino acids, peptides, dopamine and related agents, phenothiazine neuroleptics and also phenothiazines that lack neuroleptic activity, butyrophenones, diphenylbutylpiperidines such as pimozide and miscellaneous neuroleptics. The information tabulated includes the species used, route of administration and dose of drugs, the environmental temperature at which the experiments were performed, the number of tests, the direction and magnitude of body temperature change and remarks on the presence of special conditions, such as age or lesions, or on the influence of other drugs, such as antagonists, on the response to the primary drug. Most of the cited literature was published since 1965.

Sex differences in behavioral and thermal responses to pargyline and tryptophan

The effects of parenterally injected pargyline and tryptophan on rectal temperature and behavior have been studied in male and female rats. Pargyline alone (50 mg/kg) produced hypothermia in both sexes. Pargyline (50 mg/kg) followed by low doses (20--50 mg/kg) of tryptophan caused a behavioral syndrome consisting of tremor, hindlimb abduction, forepaw treading, and straub tail. In females, but not in males, hypothermia was potentiated. The same dose of pargyline followed by higher doses (60--150 mg/kg) of tryptophan produced a short hypothermia followed by a dose-dependent behavioral syndrome, hyperthermia, and mortality. On all of these measures, females responded following shorter latencies and lower doses of tryptophan. Both hypothermia and hyperthermia were observed in treated animals following pretreatment with a peripheral decarboxylase inhibitor. The results suggest a complex role for serotonin in thermoregulation. The sex differences observed suggest higher activity of serotonin in female rat brains following the drug treatment, which may be accounted for by a higher utilization rate of tryptophan.

Simulation of biogenic amine metabolism in the brain

The metabolism of a number of biogenic amines has been simulated by using data obtained from studies of the individual enzymes from pig brain. It is shown that beta-hydroxylated amines such as noradrenaline and octopamine are metabolized primarily to the alcoholic metabolite whereas amines lacking this group [e.g. dopamine (3,4-dihydroxyphenethylamine) and 5-hydroxytryptamine] are metabolized at low concentrations to give the corresponding acid. Increase in the amine concentration results in an increase in the proportion of the alcoholic metabolite formed and this may in part account for the effects of the drug reserpine on amine metabolism. The effects of disulfiram (Antabuse) and ethanol (acting through its metabolite acetaldehyde) on amine metabolism may be understood in terms of this simulated model. It is shown that drugs that affect this system also cause alterations in the steady-state concentrations of the intermediate aldehydes and the possible implications of this are discussed.