Dopamine in the hypothalamus of the cat: pharmacological characterization and push-pull perfusion analysis of sites mediating hypothermia

Antipyretic Effect of Clonidine in Intensive Care Unit Patients: A Nested Observational Study

Fever in the intensive care unit (ICU) is usually an adaptive response to infection or inflammation. Pharmacological intervention is often required in addition to addressing the underlying causes of fever. Animal studies have examined the antipyretic effect of clonidine; however, to our knowledge there are no clinical data available in humans. The observation of an antipyretic effect of clonidine was made during a single-center randomized control trial that was designed to study the effect of clonidine addition to the commonly used sedative agents in mechanically ventilated ICU patients. Forty patients 18 years or older on mechanical ventilation for 3 days or longer were randomized into 2 groups receiving clonidine and placebo. In addition to the usual sedation/analgesia, patients in the clonidine arm received enteral clonidine in doses of 0.1 mg 3 times a day (TID), which was increased to 0.2 mg TID if the hemodynamics remained stable. Vital signs, laboratory data, all cultures, and daily ICU events were recorded. The odds ratio of temperature higher than 38.3°C was 3.96 times higher in the placebo group, after adjustment for the illness severity and the time of follow-up (P = .049). A lower temperature (0.52°C) was observed in the clonidine group after adjustment for the time of follow-up (P = .006). Our report is the first of its kind in humans that demonstrates possible antipyretic properties of enteral clonidine in the critically ill intensive care unit patient.

Central dopaminergic neurotransmission plays an important role in thermoregulation and performance during endurance exercise

Dopamine (DA) has been widely investigated for its potential role in determining exercise performance. It was originally thought that DA's ergogenic effect was by mediating psychological responses. Recently, some studies have also suggested that DA may regulate physiological responses, such as thermoregulation. Hyperthermia has been demonstrated as an important limiting factor during endurance exercise. DA is prominent in the thermoregulatory centre, and changes in DA concentration have been shown to affect core temperature regulation during exercise. Some studies have proposed that DA or DA/noradrenaline (NA) reuptake inhibitors can improve exercise performance, despite hyperthermia during exercise in the heat. DA/NA reuptake inhibitors also increase catecholamine release in the thermoregulatory centre. Intracerebroventricularly injected DA has been shown to improve exercise performance through inhibiting hyperthermia-induced fatigue, even at normal ambient temperatures. Further, caffeine has been reported to increase DA release in the thermoregulatory centre and improves endurance exercise performance despite increased core body temperature. Taken together, DA has been shown to have ergogenic effects and increase heat storage and hyperthermia tolerance. The mechanisms underlying these effects seem to involve limiting/overriding the inhibitory signals from the central nervous system that result in cessation of exercise due to hyperthermia.

Administration of caffeine inhibited adenosine receptor agonist-induced decreases in motor performance, thermoregulation, and brain neurotransmitter release in exercising rats

We examined the effects of an adenosine receptor agonist on caffeine-induced changes in thermoregulation, neurotransmitter release in the preoptic area and anterior hypothalamus, and endurance exercise performance in rats. One hour before the start of exercise, rats were intraperitoneally injected with either saline alone (SAL), 10 mg kg(-1) caffeine and saline (CAF), a non-selective adenosine receptor agonist (5'-N-ethylcarboxamidoadenosine [NECA]: 0.5 mg kg(-1)) and saline (NECA), or the combination of caffeine and NECA (CAF+NECA). Rats ran until fatigue on the treadmill with a 5% grade at a speed of 18 m min(-1) at 23 °C. Compared to the SAL group, the run time to fatigue (RTTF) was significantly increased by 52% following caffeine administration and significantly decreased by 65% following NECA injection (SAL: 91 ± 14.1 min; CAF: 137 ± 25.8 min; NECA: 31 ± 13.7 min; CAF+NECA: 85 ± 11.8 min; p<0.05). NECA decreased the core body temperature (Tcore), oxygen consumption, which is an index of heat production, tail skin temperature, which is an index of heat loss, and extracellular dopamine (DA) release at rest and during exercise. Furthermore, caffeine injection inhibited the NECA-induced decreases in the RTTF, Tcore, heat production, heat loss, and extracellular DA release. Neither caffeine nor NECA affected extracellular noradrenaline or serotonin release. These results support the findings of previous studies showing improved endurance performance and overrides in body limitations after caffeine administration, and imply that the ergogenic effects of caffeine may be associated with the adenosine receptor blockade-induced increases in brain DA release.

Doxapram only slightly reduces the shivering threshold in healthy volunteers

We determined the effects of doxapram on the major autonomic thermoregulatory responses in humans. Nine healthy volunteers were studied on 2 days: control and doxapram (IV infusion to a plasma concentration of 2.4 +/- 0.8, 2.5 +/- 0.9, and 2.6 +/- 1.1 microg/mL at the sweating, vasoconstriction, and shivering thresholds, respectively). Each day, skin and core temperatures were increased to provoke sweating, then reduced to elicit peripheral vasoconstriction and shivering. We determined the sweating, vasoconstriction, and shivering thresholds with compensation for changes in skin temperature. Data were analyzed with paired t-tests and presented as mean +/- sd; P < 0.05 was considered statistically significant. Doxapram did not change the sweating (control: 37.5 degrees +/- 0.4 degrees C, doxapram: 37.3 degrees +/- 0.4 degrees C; P = 0.290) or the vasoconstriction threshold (36.8 degrees +/- 0.7 degrees C versus 36.4 degrees +/- 0.5 degrees C; P = 0.110). However, it significantly reduced the shivering threshold from 36.2 degrees +/- 0.5 degrees C to 35.7 degrees +/- 0.7 degrees C (P = 0.012). No sedation or symptoms of panic were observed on either study day. The observed reduction in the shivering threshold explains the drug's efficacy for treatment of postoperative shivering; however, a reduction of only 0.5 degrees C is unlikely to markedly facilitate induction of therapeutic hypothermia as a sole drug.

Changes in brain temperature and thermoregulation produced by destruction of medial septal neurons in rats

Brain temperatures (Tbr) of male Wistar rats were recorded at every 15 min interval for 24 h, prior to the destruction of the medial septal (MS) neurons with N-methyl-D-aspartic acid, and on the 7th, 14th and 21st days after the destruction. The capacity of the rats to regulate their body temperature under severe cold and heat was assessed by recording their Tbr when they were exposed to 5+/-1 and 37+/-1 degrees C for 2 h, before lesion and on 8th, 9th, 15th, 16th, 22nd and 23rd days after the lesion. The Tbr was decreased and its circadian variation increased after the MS lesion. On exposure to an ambient temperature of 5+/-1 degrees C the Tbr was decreased on 9th and 16th days after the lesion, when compared with the sham lesion group on identical days, though the fall in temperature was not significant on the 23rd day. The change in Tbr (compared with the sham lesion group) was not significantly different on all days of exposure to 37+/-1 degrees C. The decrease in Tbr after the MS lesion is in contrast to the hyperthermia produced by lesion of the adjoining thermoregulatory areas. The present findings suggest that the MS lesions caused an alteration in the set point of body temperature, without drastic changes in thermoregulatory ability.

Doxapram produces a dose-dependent reduction in the shivering threshold in rabbits

Dopamine is a thermoregulatory neurotransmitter that provokes hypothermia when injected in or near the hypothalamus. Doxapram stimulates release of dopamine from carotid bodies, but is known to have central effects that are probably, at least in part, similarly mediated. We thus tested the hypothesis that doxapram produces a substantial, dose-dependent reduction in the shivering threshold in rabbits. Twenty-four rabbits, anesthetized with isoflurane, were randomly assigned to 1) saline (control), 2) 0.25 mg x kg(-1) x h(-1) doxapram, or 3) 0.50 mg x kg(-1) x h(-1) doxapram. These doses are within the recommended range for humans. Body temperature was reduced at a rate of 2 degrees to 3 degrees C/h by perfusing water at 10 degrees C through a U-shaped thermode positioned in the colon. Core temperatures were recorded from the distal esophagus. A blinded observer evaluated shivering. Core temperature at the onset of shivering defined the threshold. Data were analyzed with a one-way analysis of variance; P < 0.05 was considered statistically significant. Hemodynamic and respiratory responses were comparable in the groups. The control rabbits shivered at 36.3 degrees +/- 0.3 degrees C, those given 0.25 mg x kg(-1) x h(-1) doxapram shivered at 34.8 degrees +/- 0.5 degrees C, and those given 0.50 mg x kg(-1) x h(-1) shivered at 33.7 degrees +/- 0.6 degrees C. All the shivering thresholds significantly (P < 0.001) differed from one another. The magnitude of this inhibition, if similar in humans, would be clinically important.

Simultaneous comparison of cerebral dialysis and push-pull perfusion in the brain of rats: a critical review

Over the last 30 years, studies of the in vivo activity of neurotransmitters and other endogenous factors in the brain have comprised a major effort in the neurosciences. Historically, the technology of push-pull perfusion was utilized as a major approach to investigations in this field. In the last 10 years, cerebral dialysis has been used as an alternative method essentially for the same scientific purpose, since the perfusion technique was viewed as difficult and excessively damaging to tissue. This review considers the representative literature in which both systems have been used to study local neurochemical responses to a drug or other chemical factor, a physiological condition or other situation. In addition, new experiments have been undertaken to compare, in the same animal and at the same time, the utility and properties inherent in the techniques of push-pull perfusion and cerebral dialysis in terms of the profile of a neurotransmitter activity and their local histopathological effects. A miniaturized 33/26 ga push-pull needle and a 24 ga dialysis probe were implanted simultaneously in the left and right caudate nuclei, respectively, in the anesthetized rat. An artificial cerebrospinal fluid (CSF) was perfused simultaneously through both devices at a rate of 10 microliters/min in the push-pull cannula and at 1.0 or 2.0 microliters/min in the dialysis probe. Within a series of 8-10 successive perfusions, excess K+ ions in a concentration of either 30 or 60 mM were incorporated in the CSF and delivered simultaneously to both the push-pull cannula and dialysis probe. Samples of perfusate and dialysate were assayed chromatographically by coulometric HPLC detector and quantitated in terms of the pg/min efflux of dopamine (DA), 3,4-dihydroxyphenylacetic acid (DOPAC), homovanillic acid (HVA) and 5-hydroxyindoleacetic acid (5-HIAA). The results showed that the resting level of DA was almost undetectable in dialysate samples from either structure; in push-pull perfusates the recovery of DA ranged between 7.0 to 10.0 pg/min, which was increased threefold by excess K+ ions. The recovery of DA and the three metabolites in samples of push-pull perfusate was two to four times that in samples of dialysate during the condition of excess K+ ions. Post-mortem histological analysis of the sites of perfusion and dialysis revealed little or no differences in the cytological damage induced by either the perfusion needle or dialysis probe. Finally, the advantages and limitations of each of these two experimental approaches to in vivo analysis of neurotransmitter efflux are reviewed in relation to the selection of an open or closed system for the on-line study of in vivo neurochemical events.

Neuropeptide Y perfused in the preoptic area of rats shifts extracellular efflux of dopamine, norepinephrine, and serotonin during hypothermia and feeding

This study examined the localized action of neuropeptide Y (NPY) on monoamine transmitter activity in the hypothalamus of the unrestrained rat as this peptide induced hypothermia, spontaneous feeding or both responses simultaneously. A guide tube was implanted in the anterior hypothalamic pre-optic area (AH/POA) of Sprague-Dawley rats. Then either control CSF vehicle or NPY in a dose of either 100 ng/microliter or 250 ng/microliter was perfused by push-pull cannulae in this structure in the fully sated, normothermic rat. Successive perfusions were carried out at a rate of 20 microliters/min for 6.0 min with an interval of 6.0 min elapsing between each. Samples of perfusate were assayed by HPLC for their levels of dopamine (DA), norepinephrine (NE), serotonin (5-HT) and their respective metabolites. Whereas control CSF was without effect on body temperature (Tb) or feeding, repeated perfusions of NPY over 3.0 hr caused dose-dependent eating from 4 to 39 g of food, hypothermia of 0.9 to 2.3 degrees C or both responses concurrently. As the rats consumed 11-39 g of food, the efflux of NE, MHPG, DOPAC and 5-HT was enhanced significantly, whereas during the fall in Tb the efflux of NE, DOPAC and 5-HIAA from the AH/POA increased. When the Tb of the rat declined simultaneously with eating behavior, the levels in perfusate of DOPAC and HVA increased significantly while MHPG declined. During perfusion of the AH/POA with NPY the turnover of NE declined while DA and 5-HT turnover increased during hypothermia alone or when accompanied by feeding. These results demonstrate that the sustained elevation in NPY within the AH/POA causes a selective alteration in the activity of the neurotransmitters implicated in thermoregulation, satiety and hunger. These findings suggest that both DA and NE comprise intermediary factors facilitating the action of NPY on neurons involved in thermoregulatory and ingestive processes. The local activity of NPY on hypothalamic neurons apparently shifts the functional balance of serotonergic and catecholaminergic neurons now thought to play a primary role in the control of energy metabolism and caloric intake.

A schizophrenic patient who developed extreme hypothermia after an increase in the dose of haloperidol: a case report

A patient with chronic schizophrenia, who had been treated for a long time with chlorpromazine, haloperidol, levodopa, benserazide hydrochloride, diazepam and biperiden, developed extreme hypothermia (about 32 degrees C) when the dose of haloperidol was increased because of a deterioration of the patient's mental symptoms. No other physical manifestations were observed, except bradycardia. The turnover of noradrenaline in the cerebrospinal fluid and blood was increased in association with the hypothermia in this patient. A hypothesis about the involvement of monoamine imbalance in changes in body temperature is discussed.

Stimulation of the nigrostriatal dopamine system inhibits both heat production and heat loss mechanisms in rats

The effects of stimulating the pars compacta of the substantia nigra (SNC) on thermoregulation were assessed in normal rats, in rats with chemical lesion of the SNC dopamine (DA) pathways and in rats with striatal DA receptor blockade. Electrical stimulation of the SNC produced hypothermia, decreased metabolism and/or cutaneous vasoconstriction in rats at ambient temperatures (Ta) below 22 degrees C, as well as hyperthermia and cutaneous vasoconstriction in rats at Ta of 30 degrees C. Microinjection of an excitotoxic amino acid (kainic acid) at the same brain sites also produced the same thermal responses. In vivo voltammetric studies revealed that electrical or chemical stimulation of the SNC produced an increase in striatal DA release. The enhanced striatal DA release induced by SNC stimulation was attenuated in rats after selective destruction of the nigrostriatal DA pathway by administration of 6-hydroxydopamine into the medial forebrain bundle. In addition, the magnitude of the thermal responses produced by the SNC stimulation in the cold was attenuated by selective bilateral destruction of the nigrostriatal DA pathways or selective blockade of the striatal DA produced by intrastriatal infusion of haloperidol, a DA receptor antagonist. The results indicate that stimulation of the SNC inhibits both heat production and heat loss mechanisms in the rat.

Hypothermia and feeding induced simultaneously in rats by perfusion of neuropeptide Y in preoptic area

Changes in the body temperature (Tbo) of the unrestrained rat as well as the hyperphagic-like ingestion of food were simultaneously determined during the sustained elevation of neuropeptide Y1-36 (NPY) within the anterior hypothalamic preoptic area (AH/POA). A single guide tube was implanted stereotaxically in each rat for repeated perfusions by means of push-pull cannulae of either the CSF solvent vehicle or NPY. Following postoperative recovery, each site in the AH/POA was perfused for 6.0 min at a rate of 20 microliters/min over four successive intervals at a concentration of 100 ng/1.0 microliters or 250 ng/1.0 microliters, with an interval of 6.0 min intervening between perfusions. During repeated perfusions of NPY in the fully sated and normothermic rat, concentration-dependent eating, or a hypothermia or both responses occurred simultaneously. Mean cumulative intakes of food over 3.0 h were 12.1 +/- 1.4 and 21.5 +/- 2.7 g following the 100 and 250 ng concentrations of NPY, respectively. The mean maximal declines in Tbo were -0.92 +/- 0.21 and -1.1 +/- 0.28 degrees C, respectively after the lower and higher concentrations of the peptide. Push-pull perfusions of artificial CSF control vehicle at homologous anatomical sites in the AH/POA were without effect on feeding or the Tbo of the rats. These results demonstrate that repeated and sustained elevation of NPY in the AH/POA can cause a perturbation of the neuronal mechanisms underlying the normal "set-point" for body temperature as well as satiety.(ABSTRACT TRUNCATED AT 250 WORDS)

D2 dopamine receptor-mediated mechanisms in the medial preoptic-anterior hypothalamus regulate effective defense behavior in the cat

The role of the dopaminergic innervation of the medial preoptic-anterior hypothalamus (mPO-AH) in regulating the expression of affective defense behavior in the cat has been investigated in the present study. Feline affective defense behavior, characterized mainly by autonomic arousal, ear retraction, growling, hissing and paw striking, was elicited by electrical stimulation of the ventromedial hypothalamic nucleus (VMH). Following the establishment of a stable threshold current for eliciting the hissing response of the behavior, the effect of injecting various DAergic agonists and antagonists into the mPO-AH on the hissing threshold was determined. The microinjection of the non-selective DA agonist apomorphine (0.03, 0.16, 0.33, 0.66, 1.56 and 3.3 nmol) into the mPO-AH facilitated hissing in a time- and dose-dependent manner. This effect was mimicked by the D2-selective agonist LY 171555 (0.2 and 1.0 nmol) but not by the D1-selective agonist SKF 38393 (1.7 and 17 nmol), and was blocked by the non-selective and the D2-selective antagonists haloperidol (1.3 nmol) and sulpiride (14.5 nmol), respectively. The injection of the D1-selective antagonist SCH 23390 (0.3 nmol), however, did not inhibit apomorphine-induced facilitation of hissing. In addition, the injection of haloperidol (1.3 nmol) and sulpiride (14.5 nmol), but not SCH 23390 (0.3 nmol), alone inhibited the behavior. It was therefore concluded that dopaminergic stimulation of the mPO-AH may facilitate the expression of affective defense behavior in the cat via a D2 receptor-mediated mechanism. The physiological significance of this effect and the interaction between dopaminergic, noradrenergic and serotonergic innervation of the mPO-AH in modulating the expression of affective defense behavior in response to threatening stimuli are discussed.

Microdialysis measurement of monoamine and amino acid release from the medial preoptic region of the sheep in response to heat exposure

Concentrations of monoamines and metabolites and amino acids were measured in microdialysis samples taken from the medial preoptic area of 5 conscious sheep before, during and after exposure to an ambient temperature of 45 degrees C. Concentrations of dopamine, noradrenaline and aspartate significantly increased, and those of the serotonin metabolite, 5-hydroxyindole-3-acetic acid (5-HIAA), significantly decreased during heat exposure and although panting was induced, body temperature did not change. Concentrations of noradrenaline and aspartate declined and 5-HIAA increased to preheat exposure levels during the 60 min after the ambient temperature was reduced but levels of dopamine and its metabolite, homovanillic acid, remained elevated. Dopamine, noradrenaline, 5-HIAA and aspartate concentrations were not significantly altered by isolation stress and did not show significant changes in the cortex following heat exposure. These experiments provide further support for the proposed roles of dopamine, noradrenaline, serotonin and aspartate in the neural control of autonomic thermoregulatory responses.

The effects of dopamine on temperature regulation in goldfish

Microinjections of dopamine (DA) were made into specific forebrain loci in goldfish (Carassius auratus: 40-85 g) to study the involvement of DA in behavioral thermoregulation. Injections of 25, 50, 100 and 250 ng DA into the anterior aspect of the nucleus preopticus periventricularis (NPP) led to consistent, dose-dependent decreases in selected temperature. Minor decreases or no effect on selected temperature was observed following injections of 5 or 10 ng DA. Injections of the control solution were without effect. Injections of DA into other forebrain loci, including the posterior half of the NPP, either had no thermoregulatory effect or had minor thermoregulatory effects which, in comparison, to injections into the most effective sites, were inconsistent and required larger doses to obtain. The decrease in selected temperature following injections of 100 ng DA into the anterior NPP was blocked by haloperidol, a dopaminergic antagonist, but not by phentolamine, a noradrenergic antagonist. Injections of haloperidol alone resulted in a minor, but statistically significant, increase in selected temperature. The most sensitive DA sites lie caudal to the sites most sensitive to norepinephrine within the anterior NPP. DA acts on the dopaminergic receptors of central thermoregulatory neurons in the anterior NPP of goldfish. These receptors appear to mediate behavioral responses to excessively warm environments.

Apomorphine-induced hypothermia increases during ethanol withdrawal

Changes in several measures of dopamine function have been observed following acute or chronic ethanol exposure. The present study examined the effects of chronic ethanol exposure on the hypothermia following acute administration of the dopamine agonist apomorphine. Animals withdrawn from chronic ethanol exposure showed a significantly greater decrease in body temperature following apomorphine than did ethanol-naive controls, suggesting an increase in sensitivity to dopaminergic stimulation during ethanol withdrawal.

Hypothermia: role of alpha 1- and alpha 2-noradrenergic receptors in the hypothalamus of the cat

The purpose of this study was to characterize the alpha 1- and alpha 2-noradrenergic receptor sub-types which could mediate the hypothermic response produced by norepinephrine (NE) and other alpha-noradrenergic agonists applied to the thermosensitive zone of the hypothalamus. An array of four guide tubes was implanted stereotaxically so that their tips rested just above the anterior hypothalamic, preoptic area (AH/POA) of the cat. Following post-operative recovery, a micro-injection of an agonist or antagonist of NE receptors or control CSF vehicle was given in a volume of 1.0-2.0 microliter in the AH/POA in each of the unrestrained cats. The alpha 1-noradrenergic receptor agonist, phenylephrine, but not methoxamine, applied to the AH/POA produced a dose-dependent hypothermia of up to 2.0 degrees C. When applied similarly, the alpha 2-noradrenergic agonist clonidine, as well as norepinephrine, which acts on both alpha 1- and alpha 2-noradrenergic receptors, also induced a decline in the cat's core temperature of up to 1.5 degrees C. The hypothermic response of clonidine was inhibited by pre-treatment of the AH/POA with a micro-injection of the selective alpha 2-noradrenergic blocking agent, yohimbine. However, yohimbine given similarly in the cat's AH/POA potentiated significantly both the phenylephrine and norepinephrine-induced hypothermia. The combined alpha 1-, alpha 2-noradrenergic receptor antagonist, phentolamine, also injected into AH/POA inhibited the thermolytic response evoked by both phenylephrine and norepinephrine, whereas it was virtually ineffective against the clonidine-induced hypothermia. These results, therefore, strongly suggest that both alpha 1- and alpha 2-noradrenergic receptors subserve the coordinated thermoregulatory mechanisms in AH/POA which are required for the functional dissipation of body heat and the consequent evocation of hypothermia.

CCK and other peptides modulate hypothalamic norepinephrine release in the rat: dependence on hunger or satiety

The purpose of this investigation was to determine the functional relationship between putative satiety peptides and endogenous norepinephrine (NE) activity in the hypothalamus. Permanent guide cannulae for push-pull perfusion were implanted stereotaxically in Sprague-Dawley rats so as to rest above the medial or lateral hypothalamus (LH). Post-operatively, the animals were either satiated with food and water, both available ad lib, or fasted for 18-22 hr prior to an experiment. To perfuse a site in the LH, paraventricular (PVN) or ventromedial nucleus (VMN), a concentric 29-23 ga push-pull cannula system was lowered to a pre-determined site, in most cases after catecholamine stores had been pre-labeled with [3H]-NE. During control tests, an artificial CSF was perfused at a rate of 20-25 microliter/min for 5-8 min with a 5 min interval between each sample. The addition of cholecystokinin (CCK) in a concentration of 2.0-6.0 ng/microliter to the CSF perfused in PVN or VMN of the satiated rat enhanced the efflux of NE; however, in the fasted animal CCK often suppressed the catecholamine's release. Perfused in the LH, CCK exerted opposite effects, typically augmenting NE output when the rat was fasted but not affecting the amine's activity during the sated condition. Proglumide (1.2 micrograms/microliter) attenuated CCK's effect in releasing NE when the antagonist was perfused in the PVN of the satiated rat. Similar experiments in which neurotensin (NT) was perfused in the LH, PVN and VMN revealed virtually the same inverse effects on NE release in the fasted and satiated rat, which again were anatomically specific. Finally, insulin and 2-deoxy-D-glucose (2-DG) exerted similar state-dependent effects on the release of NE within LH and PVN. Overall, the results suggest that CCK or other neuroactive peptide could serve as a "neuromodulator" of the pre-synaptic release of NE within classical hypothalamic structures which are thought to underlie both hunger and satiety. The state-dependent nature of the peptides' activity on the noradrenergic feeding mechanism implies that these substances constitute a pivotal portion of the profile of factors which impinge functionally upon the hypothalamic neurons responsible for the feeding response and its cessation.

Different roles of intrahypothalamic and nigrostriatal dopaminergic systems in thermoregulatory responses of the rat

Classically, two neurotransmitters in the brain have been implicated in thermoregulation: 5-hydroxytryptamine and norepinephrine. A dopamine action is less well-known and usually has been studied by means of pharmacological rather than physiological procedures. In the present work using a physiological approach to the problem, the role of different central dopaminergic systems in the thermoregulatory response of rats exposed to cold (4 degrees C) or warm (45 degrees C) environments has been studied. Rostral incertohypothalamic neurons in the medial preoptic area synthesized and released more dopamine in response to a warm but not to a cold environment. On the other hand DA and DOPAC levels in nigrostriatal systems were decreased by cold but not warm environments. The dopaminergic neurons projecting to nucleus accumbens or hypothalamus do not appear to be related to the thermoregulatory response in the rat.

Effects of 6-hydroxydopamine on brain catecholamines and on acute actions of ethanol in LS/Ibg and SS/Ibg mice

LS/Ibg (LS) and SS/Ibg (SS) mice differ in ethanol-induced duration of loss of righting response or sleep time, hypothermia, hyperglycemia, and blood ethanol concentrations at regaining righting response. These differences in response to ethanol are a result of differences in central nervous system sensitivity and are mediated by polygenic systems. Studies have indicated that catecholaminergic systems may be involved in the differential effects of ethanol in LS and SS lines of mice (Masserano JM, Weiner N: Investigations into the neurochemical mechanisms mediating differences in ethanol sensitivity in two lines of mice. J Pharmacol Exp Ther 221:404-408, 1982). In this study the neurotoxin, 6-hydroxydopamine (6-OHDA), intracerebroventricular, was used to test this hypothesis. Administration of 6-OHDA markedly altered thermoregulation in LS mice but produced little effect in SS mice, and ethanol-induced hyperglycemia was attenuated in both LS and SS mice by 6-OHDA. Ethanol-induced sleep time was increased in SS mice pretreated with 100 micrograms of 6-OHDA, intracerebroventricular, whereas this response in LS mice was unaffected by 6-OHDA administration. Changes in sleep time were not related to changes in blood ethanol concentrations, indicating that 6-OHDA alters ethanol-induced sleep time by mechanisms other than brain sensitivity. Levels of norepinephrine and dopamine were determined in three brain regions, and the altered capacities for thermoregulation and glucoregulation were associated with changes in hypothalamic catecholamine levels.

Effects of intrahypothalamically administered norepinephrine, serotonin and bombesin on thermoregulation in the deermouse (Peromyscus maniculatus)

Norepinephrine, serotonin, and bombesin administered intrahypothalamically affected thermoregulation in the deermouse, Peromyscus maniculatus. At a Ta of 22 degrees C, doses of 3 micrograms and 6 micrograms of NE resulted in transient hypothermia (maximum drop of 1.6 +/- 1.0 degrees C and 4.3 +/- 2.3 degrees C, respectively). A 1.5 microgram dose of 5-HT induced a persistent hyperthermia (maximum increase of 1.8 +/- 0.8 degrees C) which persisted for more than 2 h. A 6 microgram dose of 5-HT did not produce any significant effects. At a Ta of 22 degrees C, doses of 1 ng and 10 ng of bombesin produced a transient hyperthermia (maximum increase of 1.8 +/- 0.3 degree C and 2.1 +/- 1.2 degrees C, respectively) immediately postinjection. At a Ta of 5 degrees C, a 1 ng dose of bombesin resulted in a prolonged hypothermia (maximum decrease of 2.0 +/- 0.4 degrees C), while a 10 ng dose of bombesin produced a hyperthermic response (maximum increase of 1.3 +/- 0.8 degree C) at 2 h postinjection.

Disulfiram-ethanol reaction in the rat. 1. Blood alcohol, acetaldehyde, and liver aldehyde dehydrogenase relationships

Studies were carried out to determine whether the disulfiram-ethanol reaction (DER) in the rat could be correlated with blood acetaldehyde, ethanol, and liver aldehyde dehydrogenase (ALDH) inhibition. Both hypothermia and hypotension were used as indices of the DER. Female Sprague-Dawley rats were given disulfiram (DSF) (100 mg/kg, i.p.) and low and high liver ALDH determined. No effect on high Km ALDH was found. Inhibition of low Km ALDH was dependent on DSF pretreatment time, with significant inhibition observed at 6, 8, and 12 hr following DSF. In rats receiving ethanol only, maximal blood ethanol was reached within 120 min. Blood acetaldehyde was almost undetectable. No change in rat core temperature was observed. In rats pretreated with DSF (100 mg/kg, i.p.) 8 hr before ethanol challenge (1 g/kg, i.p.), a marked increase in blood acetaldehyde was found and remained elevated throughout the temperature and blood pressure monitoring period. Blood ethanol reached a maximum within 90 min and then declined. Maximal hypothermia and hypotension occurred 120 min after ethanol. The administration of the dopamine receptor blocker pimozide (0.5 mg/kg, i.p.) 60 min before ethanol challenge, attenuated the hypothermia and hypotension. Pimozide was effective when given either 60 min before ethanol or 30 min after ethanol. The onset and duration of hypothermia and hypotension during the DER appears to follow the rise and fall of blood ethanol but not blood acetaldehyde.(ABSTRACT TRUNCATED AT 250 WORDS)

Dopamine and thermoregulation: an evaluation with special reference to dopaminergic pathways

The complex role of dopamine (DA) in the diencephalic mechanisms involved in the control of body temperature is reviewed and evaluated. In the context of the monoamine theory of thermoregulation, catecholaminergic synapses in the anterior hypothalamic pre-optic area, are proposed mediate the pathways in the brain-stem which subserve heat dissipation. Within this theoretical framework, hypothalamic DA is considered to underlie a portion of the functional component of the heat loss system. This deduction is based on pharmacological studies in which both the catecholamine and receptor antagonists have been infused directly into the hypothalamus. In view of the action of DA applied to the substantia nigra and other subcortical structures, the unique anatomical circuitry of the central dopaminergic projections has also been analyzed in terms of specific connections within critical morphological regions related to thermal functions. In particular, the nigro-striatal pathway could be involved in the mediation of one or more of the different aspects of the thermoregulatory system integrating both autonomic and behavioral responses. Finally, an anatomical schema which portrays the suggested mechanisms of DA activity is presented.

Release of norepinephrine from the rat's hypothalamus perfused with alcohol: relation to body temperature

The activity of norepinephrine (NE) within the thermosensitive region of the anterior hypothalamic, pre-optic area (AH/POA) of the rat was examined in relation to changes in core temperature produced by ethyl alcohol. Following stereotaxic implantation of push-pull guide tubes, a specific site in the AH/POA, reactive or non-reactive to NE, was labeled with 1.0 microliter of [3H]-NE. Alcohol in a concentration of 2.75% or 5.5% was then perfused locally at the same site by push-pull cannulae or administered peripherally in a dose of 2.0 g/kg. In control experiments, artificial CSF was perfused alone. The perfusion of alcohol enhanced or delayed the release of [3H]-NE in AH/POA or failed to alter the efflux of the catecholamine, with the specific response dependent principally on the: (1) anatomical site of hypothalamic perfusion, (2) concentration of alcohol, and (3) interval of perfusion itself. During the perfusion of alcohol within a very circumscribed region in the AH/POA, vasodilatation, as reflected by an increase in skin temperature, and a hypothermia of short latency, occurred. The change in core temperature was usually accompanied by a delay in the efflux of [3H]-NE. After the peripheral administration of 2.0 g/kg alcohol, an alteration in NE efflux from the AH/POA was also induced during the course of a hypothermic response accompanied by vasodilatation. These results suggest that alcohol exerts a direct central effect on nerve cells comprising the thermoregulatory mechanism located within the hypothalamus. Further, the well-known thermolytic effect of alcohol could be mediated in part by noradrenergic synapses within AH/POA, by means of their phasic release of NE.

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

This survey begins 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 since 1978, but data from many earlier papers are also tabulated.

Dopamine effects on thermosensitive neurons in hypothalamic tissue slices

To understand the role of hypothalamic dopamine in thermoregulation, single unit activity was recorded in vitro, from constantly perfused tissue slices of rat preoptic area and anterior hypothalamus, PO/AH. The firing rate and thermosensitivity of individual PO/AH neurons were determined before, during and after tissue perfusion with media containing dopamine. Dopamine excited 41% of the warm-sensitive neurons, inhibited 100% of the cold-sensitive neurons, and had no effect on 83% of the temperature-insensitive neurons. In addition, dopamine decreased the local thermosensitivity of most cold-sensitive neurons. There were no major differences between these neuronal types in terms of the time course or latency of dopamine's effect. These results are consistent with the hypothesis that dopamine is involved in hypothalamic synapses controlling thermoregulatory responses which oppose increases in body temperature.

Neurotensin perfusion of rat hypothalamus: dissociation of dopamine release from body temperature change

To determine whether endogenous dopamine is involved in the impairment of body temperature induced by neurotensin, the local activity of [14C]dopamine in the hypothalamus of the unanesthetized rat was examined. A push-pull guide tube was implanted permanently above an intended site of perfusion within the anterior hypothalamic, pre-optic area or other region of the diencephalon. After the endogenous stores of dopamine at a specific site were labelled by microinjection of 0.02-0.05 muCi of [14C]dopamine, an artificial cerebrospinal fluid was perfused at the site at a rate of 20 microliter/min and at successive 5 min intervals. Perfusion of neurotensin in concentrations of 0.05 or 0.1 microgram/microliter in the dorsomedial hypothalamus, lateral hypothalamus, arcuate nucleus or diagonal band of Broca evoked a calcium-dependent efflux of [14C]dopamine. The release of dopamine induced by neurotensin was functionally specific since it was: (1) not mimicked by the relatively inactive neurotensin analogue, [D-Arg9]neurotensin; (2) dependent on the morphological locus of the push-pull perfusion; and (3) not accompanied by an efflux of [3H]norepinephrine when the site was double-labelled. Although neurotensin perfused in the anterior hypothalamic, pre-optic area caused a consistent decline in temperature, in most cases the temperature change did not correlate with an enhanced release of dopamine. Moreover, the release of dopamine, but not the temperature change, was abolished when neurotensin was perfused in a calcium-free medium. These results show that it is unlikely that the thermolytic action of neurotensin, at least within the hypothalamus, is mediated by the presynaptic release of dopamine.

In vivo release of dopamine during perfusion of neurotensin in substantia nigra of the unrestrained rat

The functional effect of neurotensin on the kinetics of dopamine (DA) release in the substantia nigra of the freely moving rat was investigated. After guide tubes for push-pull perfusion were implanted stereotaxically just above the substantia nigra, endogenous stores of DA in this structure were labelled by micro-injection of 0.02-0.05 microCi of [14C]-DA. Then an artificial cerebrospinal fluid (CSF) was perfused within the site at a rate of 20 microliters/min at successive 5 min intervals. Neurotensin added to the CSF perfusate in concentrations of 0.05-0.1 microgram/microliter evoked an immediate, Ca++ dependent release of DA from sites directly within the substantia nigra or a delayed efflux when the peptide was perfused at the edge of this structure. Neurotensin failed to affect the pattern of release of this monoamine at sites which were not within the substantia nigra. Further, the body temperature of the rat also was not altered by neurotensin at any of the sites of perfusions. A relatively inactive analogue of the peptide, [D-Arg]9 neurotensin, was essentially without effect on DA activity. In double isotope experiments in which the substantia nigra of the rat was labelled with both [3H]-5-HT and [14C]-DA, the perfusion with neurotensin failed to affect 5-HT efflux while the release of DA was enhanced. Chromatographic analysis of the metabolites of DA in samples of push-pull perfusates revealed that neurotensin enhanced significantly the level of DOPAC and HVA. Overall, these results demonstrate that in the unrestrained rat neurotensin acts selectively within the substantia nigra to alter the presynaptic, Ca++ dependent release of DA.(ABSTRACT TRUNCATED AT 250 WORDS)

Is alcohol induced poikilothermia mediated by 5-HT and catecholamine receptors or by ionic set-point mechanism in the brain?

In adult male Sprague-Dawley rats, stainless steel guide cannulae were implanted stereotaxically in either the lateral or third cerebral ventricle. Postoperatively, each animal was maintained at an ambient temperature of 22 degrees C. Just prior to the intragastric gavage of 4.0 g/kg ethyl alcohol (20% solution) individual animals were fitted with a colonic thermistor probe. Then, control CSF, a monoaminergic receptor antagonist, or a Ca++ ion chelating agent, EGTA, was infused into either the lateral or third ventricle (ICV) in a volume of 10.0 microliter. Phentolamine (20.0 micrograms), butaclamol (10.0 micrograms), or methysergide (20.0 micrograms) injected ICV all failed to prevent the thermolytic action of alcohol. The fall of 1.5 to 2.0 degrees C in the rat's colonic temperature, ordinarily caused by alcohol, was the same as that without the antagonists and lasted 3.0 to 4.0 hrs. EGTA infused into the rat's lateral cerebral ventricle also did not interfere with alcohol's poikilothermic action. However, EGTA infused into the third cerebral ventricle completely blocked alcohol's effect in lowering the body temperature of the rat. These results suggest that: (1) alcohol's profound effects on body temperature are not mediated by 5-HT, norepinephrine or dopamine pathways which are thought to underlie the mechanisms in the hypothalamus for thermoregulation; and (2) the temperature set-point mechanism, controlled by the ratio of diencephalic Na+ to Ca++ ions, is incapacitated by alcohol. Restoration of the ratio in the diencephalon by the direct, local chelation of Ca++ ions that eliminates alcohol's deleterious effects on body temperature.

In vivo dopamine release from the anterior hypothalamus of the rat

The release of dopamine from the anterior hypothalamic/preoptic region of the anesthetized rat was investigated in vivo using a superfusion technique with a push-pull cannula. Dopamine was measured electrochemically after separation by liquid chromatography. The spontaneous release of dopamine was very low but detectable in some experiments. An inhibitor of monoamine oxidase (pargyline) and the immediate precursor of dopamine (L-DOPA) were added to synthetic cerebrospinal fluid superfusing the area. When these substances were present dopamine release was increased considerably and appeared to be stable for a long period of time. Mechanisms contributing to the formation of newly synthetized dopamine are discussed in relation to the releasing effect of d-amphetamine and the inhibiting effect of calcium-free medium. The functional significance of dopamine release was shown by the increased release of dopamine following an increase in blood pressure obtained by an intraarterial injection of blood. Finally, ventral noradrenergic bundle lesion on the same side of the superfusion site considerably enhanced dopamine release which may indicate an inhibitory control of dopamine release by noradrenergic neurons. Furthermore, this experimental procedure provides valuable means for analyzing the effects of pharmacological as well as other manipulations on the dopamine released from a superfused brain area in vivo.

The role of protein synthesis in the hypothalamic mechanism mediating pyrogen fever

The effects of inhibition of protein synthesis by anisomycin on the pathogenesis of fever and normal thermoregulatory processes were investigated in the conscious and unrestrained cat. Subcutaneous administration of 5.0-25.0 mg/kg of anisomycin prevented the fever normally evoked by an intravenous infusion of either 1.0 ml (10(8) organisms) of a 1:10 dilution of S. typhosa or 1.0-5.0 ml (3.5 x 10(5)-2.1 X 10(7) cells/ml) of endogenous pyrogen. In addition, systemic pre-treatment with anisomycin delayed and/or blocked the fever typically elicited by a direct micro-injection into the anterior hypothalamic, preoptic area (AH/POA) at AP 12.5-16.0 of 1.0 microliters of the endotoxin. Anisomycin did not alter the hyperthermic response to an anterior hypothalamic injection of either 1.0-7.0 micrograms/1.0 microliters of serotonin (5-HT) or 100.0 ng/1.0 microliters of prostaglandin (PGE). Inhibition of protein synthesis, furthermore, did not prevent the fall in body temperature usually produced by an intrahypothalamic micro-injection of 2.33-14.0 micrograms/1.0 microliters of either norepinephrine (NE) or dopamine (DA). The thermoregulatory capacity of the cat was unaffected by the administration of comparable doses of anisomycin, i.e., the animal was able to maintain normal body temperature (+/- 0.5 degrees C) when exposed to an ambient temperature of either 10 degrees C or 34 degrees C. These results strongly suggest that the synthesis of new protein within the region of the AH/POA is a functional requisite for the development of a pyrogen-induced fever.

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.

Dopamine and temperature regulation in the primate: effects of apomorphine and pimozide

The purpose of this study was to determine the effects of a specific dopamine-receptor agonist (apomorphine) and antagonist (pimozide) on temperature regulation in the primate. Using 4 rhesus monkeys and 2 patas monkeys as subjects, increasing doses of apomorphine (0.05, 0.1, 0.2, 0.4, 0.6 mg/kg) injected subcutaneously produced a dose-dependent hypothermia associated with sharp elevations in tail-skin and ear pinna temperatures. Apomorphine also produced dose-related behavioral responses including salivation, hypermotility, hypersensitivity, pupil dilation and erection, suggesting a central site of action. Pre-treatment with pimozide (0.5 mg/kg, SC) blocked the apomorphine-induced hypothermia, but the subcutaneous injection of pimozide alone had no effect on body temperatures. In the patas monkey, the decline in colonic temperature following the injection of apomorphine (0.4 mg/kg) was not associated with a change in metabolic rate or heart rate. In 2 animals, mean colonic temperature fell 1.7, 0.67, and 0.3 degrees C following the injection of apomorphine ((0.4 mg/kg) in 15, 25, and 35 degrees C environments, respectively. These data suggest that the apomorphine-induced hypothermia was mediated by an increase in heat dissipation rather than a decline in heat production. The site of this drug remains to be elucidated.

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.

Fever produced by intrahypothalamic pyrogen: effect of protein synthesis inhibition by anisomycin

In the unrestrained cat, the inhibition of protein synthesis by anisomycin, given either subcutaneously (5.0--25.0 mg/kg) or directly into the anterior hypothalamic, preoptic area (1.0--25.0 micrograms) impaired the development of a bacterial fever. S. typhosa infused intravenously (1:10 dilution in 1 ml) or into AH/POA (1.0 microliter) evoked an intense fever which was either significantly delayed or prevented by anisomycin. Conversely, anisomycin failed to affect the typical hyperthermia evoked by 100 ng PGE2 or 1.0--7.0 micrograms 5-HT similarly infused into AH/POA. These data demonstrate that an intermediary humoral factor of unknown nature is required in the hyperthermic effector pathway underlying the febrile response.