5-HT receptors and hyper- or hypothermia: elucidation by catecholamine antagonists injected into the cat hypothalamus

Swim stress activates serotonergic and nonserotonergic neurons in specific subdivisions of the rat dorsal raphe nucleus in a temperature-dependent manner

Physical (exteroceptive) stimuli and emotional (interoceptive) stimuli are thought to influence stress-related physiologic and behavioral responses through different neural mechanisms. Previous studies have demonstrated that stress-induced activation of brainstem serotonergic systems is influenced by environmental factors such as temperature. In order to further investigate the effects of environmental influences on stress-induced activation of serotonergic systems, we exposed adult male Wistar rats to either home cage control conditions or a 15-min swim in water maintained at 19 °C, 25 °C, or 35 °C and conducted dual immunohistochemical staining for c-Fos, a marker of immediate-early nuclear activation, and tryptophan hydroxylase (TPH), a marker of serotonergic neurons. Changes in core body temperature were documented using biotelemetry. As expected, exposure to cold (19 °C) swim, relative to warm (35 °C) swim, increased c-Fos expression in the external lateral part of the parabrachial nucleus (LPBel), an important part of the spinoparabrachial pathway involved in sensation of cold, cutaneous stimuli, and in serotonergic neurons in the raphe pallidus nucleus (RPa), an important part of the efferent mechanisms controlling thermoregulatory warming responses. In addition, exposure to cold (19 °C) swim, relative to 35 °C swim, increased c-Fos expression in the dorsal raphe nucleus, ventrolateral part/periaqueductal gray (DRVL/VLPAG) and dorsal raphe nucleus, interfascicular part (DRI). Both of these subregions of the dorsal raphe nucleus (DR) have previously been implicated in thermoregulatory responses. Altogether, the data are consistent with the hypothesis that midbrain serotonergic neurons, possibly via activation of afferents to the DR by thermosensitive spinoparabrachial pathways, play a role in integration of physiologic and behavioral responses to interoceptive stress-related cues involved in forced swimming and exteroceptive cues related to cold ambient temperature.

Has dopamine a physiological role in the control of sexual behavior? A critical review of the evidence

The role of dopaminergic systems in the control of sexual behavior has been a subject of study for at least 40 years. Not surprisingly, reviews of the area have been published at variable intervals. However, the earlier reviews have been summaries of published research rather than a critical analysis of it. They have focused upon the conclusions presented in the original research papers rather than on evaluating the reliability and functional significance of the data reported to support these conclusions. During the last few years, important new knowledge concerning dopaminergic systems and their behavioral functions as well as the possible role of these systems in sexual behavior has been obtained. For the first time, it is now possible to integrate the data obtained in studies of sexual behavior into the wider context of general dopaminergic functions. To make this possible, we first present an analysis of the nature and organization of sexual behavior followed by a summary of current knowledge about the brain structures of crucial importance for this behavior. We then proceed with a description of the dopaminergic systems within or projecting to these structures. Whenever possible, we also try to include data on the electrophysiological actions of dopamine. Thereafter, we proceed with analyses of pharmacological data and release studies, both in males and in females. Consistently throughout this discussion, we make an effort to distinguish pharmacological effects on sexual behavior from a possible physiological role of dopamine. By pharmacological effects, we mean here drug-induced alterations in behavior that are not the result of the normal actions of synaptically released dopamine in the untreated animal. The conclusion of this endeavor is that pharmacological effects of dopaminergic drugs are variable in both males and females, independently of whether the drugs are administered systemically or intracerebrally. We conclude that the pharmacological data basically reinforce the notion that dopamine is important for motor functions and general arousal. These actions could, in fact, explain most of the effects seen on sexual behavior. Studies of dopamine release, in both males and females, have focused on the nucleus accumbens, a structure with at most a marginal importance for sexual behavior. Since accumbens dopamine release is associated with all kinds of events, aversive as well as appetitive, it can have no specific effect on sexual behavior but promotes arousal and activation of non-specific motor patterns. Preoptic and paraventricular nucleus release of dopamine may have some relationship to mechanisms of ejaculation or to the neuroendocrine consequences of sexual activity or they can be related to other autonomic processes associated with copulation. There is no compelling indication in existing experimental data that dopamine is of any particular importance for sexual motivation. There is experimental evidence showing that it is of no importance for sexual reward.

Single-unit responses of serotonergic medullary and pontine raphe neurons to environmental cooling in freely moving cats

Brain serotonin has long been implicated in the regulation of body temperature, although its precise role is not completely understood. The present study examined the effects of environmental cooling (4-8 degrees C for 2 or 4h) on the single-unit activity of serotonergic neurons recorded in the medullary raphe nuclei obscurus and pallidus and in the pontine dorsal raphe nucleus of freely moving cats. These neuronal groups have primarily descending projections to the spinal cord and ascending projections to the forebrain, respectively. Cold exposure induced shivering and piloerection, but no appreciable changes in core temperature. Of the medullary serotonergic cells studied (n=14), seven were activated and seven were unresponsive to cold exposure. For the responsive cells, the mean increase and peak effect in unit activity relative to baseline were 31% and 46%, respectively. Of the seven cold-responsive cells, the activity of four was monitored when the animals were transferred back to room temperature (23 degrees C). Within 15-30 min, the activity of these cells returned to baseline. In contrast, none of the dorsal raphe nucleus cells studied (n=14) displayed a significant change in neuronal activity during cold exposure, suggesting that these neurons do not receive afferent input from cold-sensitive cutaneous receptors or participate in thermoregulatory responses evoked by low ambient temperatures.Overall, these results suggest that a subset of medullary serotonergic neurons play a role in physiological mechanisms underlying cold defense (e.g. increases in motor output and/or autonomic outflow). On the other hand, the lack of responsiveness of serotonergic dorsal raphe nucleus neurons to cold exposure does not support a specific role for these cells in thermoregulation.

Magnolol decreases body temperature by reducing 5-hydroxytryptamine release in the rat hypothalamus

1. The effects of magnolol, isolated and purified from the cortex of Magnolia officinalis Rehd. et Wils, on thermoregulation and hypothalamic release of 5-hydroxytryptamine (5-HT) by in vivo microdialysis were assessed in normothermic rats and in febrile rats treated with interleukin-1 beta. 2. Intraperitoneal administration of magnolol (25-100 mg/kg) produced a decrease in colon temperature, an increase in foot skin temperature, a decrease in metabolic rate and a decrease in the endogenous release of 5-HT in the rat hypothalamus. 3. Depletion of rat brain 5-HT, produced by intracerebroventricular pretreatment with 5,7-dihydroxytryptamine, attenuated the magnolol-induced hypothermia, cutaneous vasodilation and decreased metabolism. 4. Intracerebroventricular administration of (+/-)-2,5-dimethoxy-4-iodoamphetamine (a 5-HT2 receptor agonist; 5-10 micrograms/5 microL) increased basal colon temperature and reversed the magnolol-induced hypothermia. 5. The increases in both colon temperature and hypothalamic 5-HT release produced by interleukin-1 beta injection were attenuated by treatment with magnolol. 6. The data suggest that magnolol decreases body temperature (due to increased heat loss and decreased heat production) by reducing 5-HT release in rat hypothalamus.

Changes in extracellular serotonin in rat hypothalamus affect thermoregulatory function

Experiments were carried out to determine the effects of altering the serotonin (5-HT) levels in the hypothalamus on thermoregulatory function in unanesthetized restrained rats. Local perfusion of the hypothalamus with dialysis solution containing 5-hydroxytryptophan (a 5-HT precursor), fluoxetine (a 5-HT reuptake inhibitor), or high potassium significantly increased both colonic temperature (Tco) and the extracellular concentrations of 5-HT in the hypothalamus. Reciprocally, both extracellular concentration of 5-HT in the hypothalamus and Tco were decreased with a dialysis solution containing tetrodotoxin (which blocks the voltage-dependent sodium channel), zero calcium concentration, or systemic administration of 8-hydroxy-2-(di-n-propylamino) tetralin (8-OH-DPAT,5-HT1A agonist). Intrahypothalamic administration of 8-OH-DPAT and (2,5-dimethoxy-4-iodophenyl)-2-aminopropane (a 5-HT2 agonist) produced hypothermic and hyperthermic effects, respectively. The results indicate that elevating the 5-HT levels in the hypothalamus activates postsynaptic 5-HT2 receptors and results in hyperthermic effects, whereas stimulation of presynaptic 5-HT1A receptors in the hypothalamus reduces the endogenous 5-HT release and results in hypothermic effects.

Action of harman (1-methyl-beta-carboline) on the brain: body temperature and in vivo efflux of 5-HT from hippocampus of the rat

Harman (1-methyl-beta-carboline) has been shown previously to act on the hippocampus of the rat in terms of its evocation of anxiogenic responses and induction of alcohol preference. In the present experiments, the localized perfusion of 200 microM harman in the dorsal hippocampus of freely moving rats increased the levels of serotonin (5-HT) but not 5-hydroxyindoleacetic acid (5-HIAA) in cerebral dialysates. The systemic administration of 5.0-20 mg/kg harman also enhanced 5-HT in the perfusates but reduced the levels of 5-HIAA in a dose-dependent manner, probably as a result of the inhibition of the enzyme monoamine oxidase type A (MAO-A). Harman given systemically in doses of 2.5-20 mg/kg induced an intense hypothermia, with a maximum fall produced by the 5.0 mg/kg dose. This fall in body temperature (Tb) induced by 5.0 mg/kg harman was not antagonized by 5.0 mg/kg of (+/-)-pindolol. Further, pretreatment of the rats with parachlorophenylalanine (pCPA) also failed to alter the harman-induced hypothermia. The systemic administration of 10 mg/kg of the MAO-A inhibitor, clorgyline, also lowered Tb significantly. Overall, the present experiments show that harman apparently influences 5-HT systems in the brain by its action in inhibiting MAO-A. This property is likely responsible also for the harman-induced increase of 5-HT in the hippocampus of the rats.

Fever and feeding in the rat: actions of intrahypothalamic interleukin-6 compared to macrophage inflammatory protein-1 beta (MIP-1 beta)

The chemokines, macrophage inflammatory protein-1 (MIP-1) and its subunit MIP-1 beta, induce an intense fever in the rat when they are injected directly into the anterior hypothalamic, pre-optic area (AH/POA), a region containing thermosensitive neurons. The purpose of this study was to compare the central action on body temperature (Tb) of MIP-1 beta with that of interleukin-6 (IL-6), which also has been implicated in the cerebral mechanism underlying the pathogenesis of fever. Following the stereotaxic implantation in the AH/POA of guide cannulae for repeated micro-injections, radio transmitters which monitor Tb continuously were inserted intraperitoneally in each of 15 male Sprague-Dawley rats. Each micro-injection was made in a site in the AH/POA in a volume of 1.0 microliter of pyrogen-free artificial CSF, recombinant murine MIP-1 beta, or recombinant human IL-6. MIP-1 beta in a dose of 25 pg evoked an intense fever characterized by a short latency, a mean maximum rise in Tb of 2.4 +/- 0.21 degrees C reached by 3.7 +/- 0.42 hr, and a duration exceeding 6.5 hr. Injected into homologous sites in the AH/POA, IL-6 induced a dose dependent fever of similar latency and a mean maximal increase in Tb of 1.2 +/- 0.25 degrees C, 1.8 +/- 0.15 degrees C, and 2.1 +/- 0.22 degrees C and duration of 6.2 +/- 1.28 hr, 6.7 +/- 0.49 hr, and 6.8 +/- 0.65 hr when given in doses of 25, 50, and 100 ng, respectively.(ABSTRACT TRUNCATED AT 250 WORDS)

Action of cyclosporine on fever induced in rats by intrahypothalamic injection of macrophage inflammatory protein-1 (MIP-1)

In order to examine the central mechanism of pyrexic action of macrophage inflammatory protein-1 (MIP-1), guide cannulae for injections were implanted stereotaxically just above the anterior hypothalamic, pre-optic area of the rat. Following post-operative recovery, the body temperature (Tb) of each rat was monitored by a colonic thermistor probe over a test interval of 4 hr. Injected in a 0.5 microliter volume into the anterior hypothalamic pre-optic area, MIP-1, in a dose of 5.6 or 28 pg, evoked an intense fever with a latency of 15-30 min. Pretreatment of the anterior hypothalamic pre-optic area with 1.0 microgram cyclosporine A (CsA), delivered in a volume of 0.5 microliter, delayed the onset of the fever induced by 5.6 pg MIP-1, injected at the same site. Similar injections of CsA also attenuated significantly the magnitude of the fever, following either the 5.6 or 28 pg dose of MIP-1. As a systemic control, 15 mg/kg CsA was administered intraperitoneally, 2.0 hr before the injection of MIP-1 in the anterior hypothalamic pre-optic area. By this route, CsA also delayed the rise in temperature but the fever induced by 5.6 pg MIP-1 reached the same magnitude as that after MIP-1 alone. Conversely, intraperitoneal administration of CsA did not antagonize the pyrexic response evoked by 28 pg MIP-1, injected into the anterior hypothalamic pre-optic area, but rather enhanced the fever.(ABSTRACT TRUNCATED AT 250 WORDS)

Fever induced by macrophage inflammatory protein-1 (MIP-1) in rats: hypothalamic sites of action

The purpose of this study was to clarify the central site of action as well as functional characteristics of the febrile response of the cytokine, macrophage inflammatory protein-1 (MIP-1). Guide cannulae for microinjection were implanted stereotaxically in the rat just above the pyrogen and thermosensitive area of the anterior hypothalamic, preoptic area (AH/POA). Following postoperative recovery, the body temperature of each rat (Tbo) was monitored during an experiment by a colonic thermistor probe at 0.5-1.0-h intervals. When MIP-1 was microinjected in a 0.5-microliter volume into the AH/POA in one of eight concentrations ranging from 0.0028 nanograms (ng) to 9.0 ng, an intense monophasic or biphasic fever was evoked. The MIP-1-induced increase in the Tbo of the rat was characterized by its short latency of 15 to 30 min and an inverse dose-response curve. Measures of mean latency and maximal rise in Tbo following MIP-1 confirmed the potency of this dose. Although the dose of 0.028 ng produced a fever of over 2.0 degrees C with a latency of only 15 min or less, the hyperthermic response became less intense as the dose of MIP-1 was increased. An anatomical mapping of sites of microinjection which reacted to MIP-1 in mediating fever revealed that the medial portion of the POA of the rat just rostral to the border of the AH was the region of maximum sensitivity to the cytokine.(ABSTRACT TRUNCATED AT 250 WORDS)

Hypothalamic indomethacin fails to block fever induced in rats by central macrophage inflammatory protein-1 (MIP-1)

This investigation examined the extent to which the activity of a prostaglandin (PG) in the anterior hypothalamic, preoptic area (AH/POA) of the rat plays a role in the intense fever induced by macrophage inflammatory protein-1 (MIP-1) applied directly to this anatomical region. For the microinjection of both a PG synthesis inhibitor, indomethacin, and MIP-1 into sites within the AH/POA, guide cannulae were implanted chronically just above this pyrogen-reactive region. Postoperatively, the body temperature (Tb) of each rat was monitored in the unrestrained condition by means of a colonic thermistor probe. MIP-1 microinjected into the AH/POA in a 0.5-microliter volume evoked a biphasic fever when given in a dose of 5.6 picograms (pg) and a monophasic fever in a dose of 28 pg. The latency of the febrile response was ordinarily 15 min with an asymptote of 1.5 degrees C reached ordinarily within 2.0-2.5 h. When the cytokine-reactive site in the AH/POA was pretreated with indomethacin microinjected in an efficacious dose of 0.5 microgram, the MIP-1 fever evoked by 5.6 pg was not inhibited. Further, pretreatment of AH/POA sites with indomethacin prior to the higher 28-pg dose of MIP-1 delayed the febrile response but did not block it. As a systemic control, indomethacin also was administered intraperitoneally in a dose of 5.0 mg/kg, again 15 min prior to the microinjection of MIP-1 into the AH/POA. In this case, indomethacin only partially attenuated but did not block the fever evoked by either dose of MIP-1.(ABSTRACT TRUNCATED AT 250 WORDS)

Macrophage inflammatory protein-1: unique action on the hypothalamus to evoke fever

Macrophage inflammatory protein (MIP-1) administered systemically causes a fever not blocked by a prostaglandin (PGE) synthesis inhibitor. The purpose of this study was to examine the central mechanism of pyrexic action of this cytokine in the unrestrained rat. After guide cannulae for microinjection were implanted stereotaxically just above the anterior hypothalamic preoptic area (AH/POA), the body temperature of each rat was monitored by a colonic thermistor probe. Saline control vehicle or MIP-1 was microinjected into the AH/POA in one of eight concentrations ranging from 0.0028-9.0 ng per 0.5 mu 1 volume. MIP-1 induced a biphasic or monophasic fever of short latency characterized by an inverse dose-response curve. The potency of MIP-1 was in the femtomolar (10(-15)) range with the lowest dose of 0.028 ng producing a fever of over 2.0 degrees C with a latency of 15 min or less. To determine whether a PGE mediates MIP-1 fever, indomethacin was administered either intraperitoneally in a dose of 5.0 mg/kg or directly into the MIP-1 injection site in a dose of 0.5 microgram/0.5 mu 1, both injected 15 min before MIP-1. Pretreatment of the injection site in the AH/POA with indomethacin failed to prevent the febrile response evoked by MIP-1 injected at the same locus. Further, the dose of systemic indomethacin, which blocks PGE-induced fever in the rat, attenuated only partially the MIP-1 fever. The results demonstrate that MIP-1 is the most potent endopyrogen discovered thus far, and that its action is directly in the region of the hypothalamus which contains both thermosensitive and pyrogen-sensitive neurons. The local action of MIP-1 on cells of the AH/POA in evoking fever is unaffected by the PGE inhibitor which indicates, therefore, that a cellular mechanism operates in the hypothalamus to evoke fever independently of the central synthesis of a PGE.

Temperature-related release of serotonin from unrestrained rats' pre-optic area perfused with ethanol

The circumscribed effect of ethyl alcohol on the local efflux of serotonin (5-HT) within the thermosensitive region of the anterior hypothalamic, pre-optic area (AH/POA) of the unrestrained rat was examined in relation to core temperature. A single guide cannula for push-pull perfusion was implanted stereotaxically in the AH/POA within coronal planes AP 7.0-8.2. Following 3-4 push-pull perfusions with control artificial CSF of a site identified as reactive to 5-HT, ethanol in a concentration of 2.75 (471 mM) or 5.5 (942 mM) percent was perfused at the same locus over a 5-10 min interval. Successive samples of perfusate were assayed for their content of 5-HT by high performance liquid chromatography using electrochemical detection (HPLC-EC). Within a circumscribed region of the AH/POA of the rat maintained at an ambient temperature of 22 degrees C, ethanol induced either an immediate or delayed hypothermia of short latency or a transient decline followed by an immediate increase in core temperature. In each case, the shift in temperature depended on the anatomical site of push-pull perfusion. Overall, the fall in core temperature was accompanied by an inhibition in the efflux of 5-HT. However, the consequent rise in the rat's core temperature was associated with an enhanced release of 5-HT in the samples of perfusate collected from the AH/POA. These results suggest that serotonergic synapses within the AH/POA are apparently involved in the thermolytic effects of ethanol as well as in the thermogenesis following the interval of heat loss.

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

This survey continues a second series of compilations of data regarding changes in body temperature induced by drugs and related agents. The information listed includes the species used, the route of administration and dose of drug, the environmental temperature at which experiments were performed, the number of tests, the direction and magnitude of change in body temperature and remarks on the presence of special conditions, such as age or brain lesions. Also indicated is the influence of other drugs, such as antagonists, on the response to the primary agent. Most of the papers were published from 1980 to 1984 but data from many earlier papers are also tabulated.

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)

Octopamine action on the spontaneous contractions of the isolated nerve cord of Lumbricus terrestris

Octopamine and synephrine were observed to effect the spontaneous rhythmic contractions displayed by the isolated ventral nerve cord of the earthworm, Lumbricus terrestris. octopamine and synephrine produced dose-dependent significant changes in the frequency, amplitude and basal tonus of the spontaneous contractions. Application of adrenergic receptor antagonists suggested the octopamine receptors to have some similarity to vertebrate alpha 1-adrenergic receptors. The spontaneous contractions were not abolished by tetrodotoxin (TTX) which suggested a myogenic origin for the contraction of the ventral nerve cord sheath muscles. Octopamine, in the presence of TTX, increased the basal tonus and maximum force of the spontaneous contractions.