Peptides and thermoregulation

Centrally administered MTII affects feeding, drinking, temperature, and activity in the Sprague-Dawley rat

MTII, an agonist of melanocortinergic receptors, is a well-documented anorexigenic agent in rats. Many investigators have reported its effects on feeding without considering concurrent alterations in other behaviors. Accordingly, we performed studies to simultaneously measure nocturnal feeding, drinking, activity, and temperature of rats after intracerebroventricular (third ventricle) administration of a wide dose range of MTII (0.05-500 ng). We observed that MTII modulates these physiological parameters in a dose-dependent manner. Low doses of MTII (0.05 ng) caused reductions in feeding without alterations in body temperature, drinking, or activity. In contrast, hyperthermia and disrupted drinking patterns, along with food intake reductions, were evident at doses exceeding 50 ng. The fact that low doses altered only feeding, whereas higher doses affected a range of parameters, suggests that certain melanocortin-induced behavioral changes may be mediated by distinct populations of melanocortin receptors with varying affinities or that those changes seen at higher doses may be nonspecific in nature.

Cardiovascular and hormonal responses to hyperthermic stress in cocaine addicts after a long period of abstinence

In order to study the effects of exposure to heat, cardiovascular and hormonal responses were measured in 10 male cocaine addicts (after 4 weeks and 1 year of abstinence) and in 10 normal men. Subjects sat for 30 minutes in a sauna room. Hormonal (ACTH, beta endorphin, (beta EP) met enkephalin (met-enk), prolactin (PRL), cortisol) and cardiovascular parameters (heart rate, systolic and diastolic blood pressure) were measured before and after heat exposure. Basal levels of ACTH, beta EP, Met-Enk and cortisol were similar in normal and in cocaine addicts, whereas plasma PRL values were higher in drug abusers after long-term abstinence. All the examined hormones, with the exception of Met-Enk, were significantly raised in normal control subjects at the end of sauna. In contrast, no significant hormonal response to hyperthermia was observed in cocaine addicts either after 4 weeks and 1 year of abstinence. No changes were detected in heart rate and blood pressure in each group, indicating that the cardiovascular adaptive responses to hyperthermia in cocaine addicts was unaltered. The results of the present study provide evidence of an impairment of the hormonal response to hyperthermia in cocaine abusers. In conclusion, cocaine abuse produces alteration in the hypothalamic-pituitary function which persists after a long period of abstinence.

Limited proteolysis and physiological regulation: an example from thyrotropin-releasing hormone metabolism

Proteases like trypsin, elastase, and many others play important regulatory functions by generating new biologically active molecules through limited proteolysis of larger proteins and peptides. The limited proteolysis of thyrotropin-releasing hormone (TRH) by Pyroglutamate aminopeptidase yields cyclo(His-Pro) or CHP, a new biopeptide associated with a variety of pharmacological activities, including regulation of body temperature, inhibition of prolactin secretion, and modulation of motor functions. Although the mechanism by which CHP elicits these biological activities is not well understood, it appears that the cyclic peptide may function at least in part by modulating central amine transport mechanisms.

Food intake and food choice: the role of the endogenous opioid peptides in the marsupial Sminthopsis crassicaudata

Endogenous opioid peptides activate food seeking behaviour and influence macronutrient choice in a number of animal species and previous studies have suggested that the palatability of food is strongly modulated by the opioid feeding system. The effect of opioid peptides on appetite and food choice in marsupials has not been evaluated. The aim of these studies was to determine the effect of mu, delta and K opioid receptors on food intake and food choice in the marsupial Sminthopsis crassicaudata. When offered a choice of mealworms or laboratory diet after 24 h food deprivation, S. crassicaudata ate predominantly mealworms. After a 24 h fast, adult male S. crassicaudata were injected peripherally with opioid receptor antagonists or saline. Animals were re-fed with either their laboratory diet alone, or a choice of laboratory diet and mealworms. In animals re-fed with laboratory diet alone, naloxone at doses of 15 and 10 mg/kg produced a 31% (P < 0.05) and 38% (P < 0.05) respectively reduction in food intake in the first 30 min after laboratory diet was re-introduced, but lower doses had no effect. The selective delta antagonist naltrindole at 20 mg/kg resulted in a 65% (P < 0.01) reduction in food intake compared to controls between 30 and 60 min. The selective kappa opioid antagonist nor-binaltorphimine had no effect on the intake of laboratory diet. In animals offered a choice of laboratory diet and mealworms, naloxone doses of 1, 5, 10, 15 and 20 mg/kg significantly decreased intake in the first 0.5 h after re-feeding, due to a preferential suppression of the intake of mealworms. Naltrindole and nor-binaltorphimine had no effect on food choice. These studies demonstrate that endogenous opioid peptides influence both food intake and choice in S. crassicaudata and that the role of the opioid feeding system is in part modulated by food palatability. In S. crassicaudata these effects appear to occur predominantly by a mu opioid receptor mechanism.

Interaction of cholecystokinin and somatostatin with a selective mu-opioid agonist and mu- and kappa-antagonists in thermoregulation

We examined the effects of intracerebroventricular (i.c.v.) injections of cholecystokinin-octapeptide (CCK-8) and somatostatin (SST) and the interactions of these neuropeptides with the selective opioid antagonists, CTAP (mu) and nor-BNI (kappa) and the mu-agonist, PL017, on body temperature (Tb) of the rat at normal ambient temperature (21 +/- 0.5 degrees C). CCK-8 produced short-lasting (15-60 min), dose-related increases in Tb in a dose range of 20 to 900 ng but did not change the Tb at lower doses (0.1-2 ng). Lower doses of SST (1 and 2 micrograms) produced hyperthermia (30-60 min) and a higher dose of SST (10 micrograms) caused hypothermia (30-45 min). PL017 (1 microgram, i.c.v.), alone and in combination with CCK-8, produced hyperthermia. The CCK-8 (300 ng)-induced hyperthermia was blocked by pretreatment of rats with CTAP (1 microgram, i.c.v.), suggesting that the higher doses of CCK-8 increase Tb through the interaction with mu-receptors or the enhancement of release of endogenous opioids acting on the mu-receptor. The hyperthermia elicited by a lower dose of SST (1 microgram) was prevented by pretreatment with CTAP but not with nor-BNI (1 microgram, i.c.v.). Pretreatment with nor-BNI blocked the higher dose (10 micrograms) of SST-induced hypothermia. PL017 or CTAP did not prevent the hypothermic effect of that dose of SST. These results indicate that a lower dose of SST (1 microgram) stimulates the mu-receptor (directly or indirectly) and a higher dose (10 micrograms) interacts with the kappa-receptor in regulation of Tb. Thus, the effects of both CCK-8 and SST on Tb appear to involve the endogenous opioid system.

Cyclo (His-Pro) modulation of body temperature at hot ambient temperature in the desert rat (Mastomys natalensis)

Cyclo(His-Pro) (CHP) has been shown to facilitate cold-induced hypothermia in the desert rat Mastomys natalensis. In the present study, we examined the role of endogenous CHP in hyperthermia induced by hot ambient temperature (40 degrees C) in the above rodent species. The results of these studies show that housing rodents at 40 degrees C resulted in a altered distribution of CHP in the brain, with a rise in hypothalamic content accompanied by an increase in rectal temperature. While administration of exogenous CHP decreased hyperthermia, immunoneutralization of endogenous CHP increased hyperthermia. The results of these studies show that changes in endogenous CHP levels may affect body temperature regulation.

Attenuation of alcohol-induced hypothermia by cyclo (His-Pro) and its analogs

Acute administration of cyclo (His-Pro) to rats cause a dose-dependent decrease in ethanol-induced hypothermia. Bromination of the imidazole moiety of histidine in cyclo (His-Pro) resulted in a significant increase in its potency to attenuate ethanol hypothermia. In contrast, benzylation of the imidazole moiety of histidine or the substitution of one or both of the amino acids in cyclo(His-Pro) led to a total loss of its thermomodulatory activity. In conclusion, it appears from these preliminary data that it may be possible to design analogs of CHP that may be effective antagonists for ethanol hypothermia.

Reductions in body weight following chronic central opioid receptor subtype antagonists during development of dietary obesity in rats

Acute administration of long-acting general opioid antagonists reduces body weight and food intake in rats. In contrast, chronic administration of short-acting general opioid antagonists produces transient effects. The present study evaluated whether chronic central administration of selective long-acting antagonists of mu (beta-funaltrexamine, BFNA, 20 micrograms), mu1 (naloxonazine, 50 micrograms), delta1 ([D-Ala2,Leu5,Cys6]-enkephalin, DALCE, 40 micrograms), delta2 (naltrindole isothiocyanate, NTII, 20 micrograms) or kappa (nor-binaltorphamine, NBNI, 20 micrograms) opioid receptor subtypes altered weight and intake of rats exposed to a palatable diet of pellets, fat, milk and water, relative to pellet-fed and diet-fed controls. Diet-fed rats receiving chronic vehicle injections significantly increased weight (7-10%) and intake over the 11-day time course. Weight was significantly reduced over the time course in rats administered either BFNA (9%), naloxonazine (12%), DALCE (7%) or NTII (6%). Initial weight reductions failed to persist following chronic NBNI. All antagonists chronically reduced fat intake, but did not systematically alter total intake, pellet intake or milk intake relative to the pattern of weight loss. These data indicate that central mu, mu1, delta1, delta2, and, to a lesser degree, kappa receptors mediate long-term opioid modulation of weight even in animals maintained on diets that ultimately result in dietary obesity.

Bioactive cyclic dipeptides

Cyclic dipeptides are among the simplest peptide derivatives commonly found in nature. Most cyclic dipeptides found to date appear to have emerged as by-products of fermentation and food processing. However, many are endogenous to members of animal and plant kingdoms; these include cyclo(Pro-Leu), cyclo(Pro-Val), cyclo(Pro-Phe), cyclo(Ala-Leu), cyclo(Pro-Tyr), cyclo(Pro-Trp), and cyclo(His-Pro). Although the five cyclic dipeptides--cyclo(His-Pro), cyclo(Leu-Gly), cyclo(Tyr-Arg), cyclo(Asp-Pro), and cyclo(Pro-Phe)--exhibit interesting physiological and/or pharmacological activities in mammals, only one of these, cyclo(His-Pro), has been conclusively shown to be endogenous to mammals. On the other hand, cyclo(Leu-Gly), cyclo(Tyr-Arg), and cyclo(Asp-Pro) are structurally related to endogenous peptides Pro-Leu-Gly-NH2 (melanocyte-stimulating hormone release inhibiting factor), Tyr-Arg (kyotorphin), and Val-Pro-Asp-Pro-Arg (enterostatin), respectively, which may serve as precursor peptides. It needs to be determined, however, whether these peptides can indeed result from the processing of their respective precursors. In conclusion, it appears that cyclic dipeptides are a relatively unexplored class of bioactive peptides that may hold great promise for the future.

Role of endogenous cyclo(His-Pro) in cold-induced hypothermia in the desert rat (Mastomys natalensis)

Central administration of exogenous cyclo(His-Pro) (CHP) is known to produce hypothermia in rodents. In the present study, we examined the role of endogenous CHP in cold-induced hypothermia in the desert rat, Mastomys natalensis. The results of these studies show that a rise in hypothalamic CHP content accompanied a decrease in rectal temperature during cold exposure. Immunoneutralization of endogenous CHP resulted in a significant decline in cold-induced hypothermia. In addition, central administration of cyclo(Ala-Gly), a structural analogue of CHP, also led to a decrease in cold-induced hypothermia. The results of these studies show that changes in endogenous CHP levels may affect body temperature regulation.

Modulation of learning, pain thresholds, and thermoregulation in the rat by preparations of free purified alpha-linolenic and linoleic acids: determination of the optimal omega 3-to-omega 6 ratio

Ingested polyunsaturated fatty acids are postulated to lead to changes in central nervous system activity, presumably by altering the lipid composition of neuronal membranes. In support of this hypothesis, we and other investigators have previously demonstrated cognitive effects in rats fed oils that contain both alpha-linolenic acid (18:3 omega 3) and linoleic acid (18:2 omega 6), with the relative content of alpha-linolenic acid being seen as the critical variable. The present study in rats examined the effects of preparations containing different ratios of highly purified free alpha-linolenic acid to linoleic acid (about 25 mg/kg of body weight daily) on learning performance (Morris water tank), pain thresholds (heated plate), and thermoregulatory control of d-amphetamine-induced hypothermia during 4 weeks of treatment. Preparations with omega 3-to-omega 6 ratios ranging from 1:3.5 to 1:5 (specifically a ratio of 1:4) produced significant favorable effects on all of these variables. Although the specific mode of action remains to be elucidated, these results suggest that such preparations of free fatty acids should be evaluated in the treatment of memory disorders and pain conditions.

Galanin antagonists block galanin-induced feeding in the hypothalamus and amygdala of the rat

Galanin significantly increased food intake when microinjected into the region of the central nucleus of the amygdala as well as into the paraventricular nucleus of the hypothalamus. In the amygdala this effect was specific to feeding; no change in grooming, resting, or other behaviour was observed after galanin treatment. These results provide evidence that the amygdala may be an important site in the mediation of galanin-induced feeding. The galanin receptor antagonists, C7 and M40, antagonized galanin-induced feeding, while having no effect alone on food consumption in free-feeding rats. These new galanin receptor antagonists provide useful tools for further investigating the role of endogenous galanin in the regulation of feeding.

Hyperthermia and endorphins

This paper discusses the role of endogenous opioids in response to hyperthermia and the alterations observed in drug or alcohol addicts. Endorphins, rather than enkephalins are involved in adaptation to heat in the central nervous system. The pituitary secretion of beta endorphin together with ACTH in response to thermal stress provided the opportunity to measure the opioid reactivity to hyperthermia in health and toxicomania, as an index of opioid function, in adaptation to heat. The review of the data in the literature shows absent responses of beta endorphin and its related hormone ACTH to the thermal stress of sauna in heroin, cocaine or alcohol addicts. A common explanation for this phenomenon is that the long-term stimulation of hypothalamic opioid neurotransmission that is produced directly or indirectly by heroin, alcohol or cocaine, disrupts the opioid response to thermal stress, and thus the adaptation to heat.

The facilitative effects of alpha-MSH and melanin on learning, thermoregulation, and pain in neonatal MSG-treated rats

Administration of monosodium glutamate (MSG) in the neonatal period renders the rat to be alpha-MSH deficient later in life. In this study rats received MSG in their neonatal period and were examined at the age of 60 days. alpha-MSH caused hypothermia, potentiated induced hypothermia, blocked paradoxical behavioral thermoregulation, improved performance in the Morris water tank, but had no effect on pain threshold. Melanin only caused an increase in pain threshold. It is suggested that the differential effect of alpha-MSH and melanin is governed by the dopaminergic system.

Morphine effects on maternal aggression, pup care and analgesia in mice

In order to assess the respective contribution of opioid receptors to the behavioral and physiological characteristics of lactating animals, we challenged mice with morphine at different phases of the lactation period. Sensitivity to morphine's effects on aggressive behavior, pup care, pain response and body temperature were measured. Lactating mice were assigned to 1 of the 3 weeks of lactation and to 1 of 5 doses of morphine sulfate (0, 1, 3, 6, 10 mg/kg IP). After morphine administration, rectal temperature and tail flick were assessed. Behavior towards three pups was observed for 5 min, followed by an aggression test with a female intruder. Morphine significantly increased the latency to retrieve pups and decreased aggressive behavior at doses that do not decrease motoric activity. Compared to virgin mice, lactating females are less sensitive to the analgesic actions of morphine but similarly sensitive to its hypothermic properties. The fact that virgin and lactating females can be distinguished on the basis of their sensitivity to morphine-induced analgesia suggests that lactating animals undergo functionally relevant changes in opioid regulation of pain sensitivity. Furthermore, morphine's specific and potent inhibition of pup retrieval supports the hypothesis that decreased opioid peptide activity is important for the expression of certain postpartum behaviors.

DSIP--a tool for investigating the sleep onset mechanism: a review

Delta-Sleep-Inducing Peptide (DSIP) has several physiological effects in addition to its ability to promote sleep in animals under certain conditions. These effects include modification in thermoregulation, heart rate, blood pressure, pain threshold, and in the lymphokine system. DSIP effects are circadian cycle-dependent. Moreover, some of DSIP effects appear before neurological or behavioral signs of sleep. DSIP may promote peripheral preparatory physiological mechanisms associated with sleep onset.

Neuropeptide-dopamine interactions. I. Dopaminergic mechanisms in cyclo(His-Pro)-mediated hypothermia in rats

Administration of cyclo(His-Pro) to rats produces a dose-dependent hypothermia that is attenuated by dopaminergic antagonists. Chronic treatment with cyclo(His-Pro) potentiates hypothermia induced by apomorphine. These results suggest that cyclo(His-Pro) acts via a dopaminergic mechanism to modulate body temperature.

The effects of DSIP on pain threshold during light and dark periods in rats are not naloxone-sensitive

The effects of Delta-Sleep-Induced Peptide (DSIP) were examined in rats kept at 12:12 light:dark schedule. The peak of the circadian pain threshold of saline-treated rats occurred at 10:00. Rats treated with 0.1 mg/kg, i.p. DSIP exhibited a significantly higher pain threshold level (as measured by hot plate) both in the light and dark periods. Prior to the treatment the peak was at 10:00. With treatment the peak shifted to 18:00. A dose of 1.0 mg/kg DSIP increased the pain threshold level only during the dark period. The analgesia induced by DSIP is insensitive to naloxone pretreatment.

The role of cholecystokinin octapeptide in the central control of food intake in the dog

Cholecystokinin octapeptide (CCK-8, 1, 190 pmol/5 min) decreased food intake and water consumption in two models of ingestive behavior, i.e., food deprivation-induced feeding and insulin-induced feeding, when administered into the third (3V) and lateral (LV) cerebral ventricles. In fasted dogs, the suppression of food intake was more prominent after 3V CCK-8, whereas intravenously administered CCK-8 was without effect. Neuropeptide Y (NPY, 1, 190 pmol) had no significant stimulatory effect on food intake and water consumption in fasted as well as satiated dogs, and actually reduced both food and water intake in insulin-treated dogs. There was a slight but significant decrease in food and water intake after 275 nmol naloxone administration in both feeding models, and some of the dogs vomited. In insulin-treated animals, CCK-8 reversed, but NPY potentiated the hypothermic phase of temperature response observed after saline administration, whereas naloxone failed to alter rectal temperature. These results suggest that the effect of CCK-8 on feeding seems to involve central mechanisms in the dog, and that the mechanisms by which CCK-8, NPY and naloxone affect feeding behavior are different.

Effects of DSIP, 5-HTP and serotonin on the lymphokine system: a preliminary study

Short term effects of the sleep promoting substances DSIP, 5-HTP and 5-HT on the function of the lymphokine system were studied 10 and 30 min after treatment. DSIP treatment after 10 and 30 min caused a significant decrease in IL-3 and CSF levels, response to CSF-1 and CSF-GM, IL-2 level, number of IL-2 receptors and in cell proliferation. DSIP initially induced (after 10 min) a decrease to be followed (after 30 min) by an increase in IL-1 level. Ten minutes after 5-HTP treatment a decrease was found in all parameter tests, except in IL-3 and in CSF secretion. 5-HT treatment was able to induce an increase in IL-3 level, a decrease in response to IL-2 receptors and proliferation, 10 min after treatment. Thirty minutes after treatment, only IL-3 and IL-2 levels were reduced. These results showed that sleep promoting substances had an effect on the lymphokines system, that DSIP was the most potent agent, that immunological changes occur before physiological or behavioral signs. The relative weak potency 5-HTP and 5-HT, and the similar pattern of effects between them, may indicate that peripheral events may lead to sleep state.

Regional distribution of in vitro release of thyrotropin releasing hormone in rat brain

To increase our knowledge of the TRH functions in brain and the processes of TRH compartmentalization and release, we studied the in vitro release of endogenous TRH in different brain areas. We also determined the correlation between TRH levels and release under both basal and stimulated conditions. TRH concentration was measured in tissues and media by specific radioimmunoassay. TRH-like material detected in olfactory bulb and hypothalamic incubates (basal or K+ stimulated) were shown to be chromatographically identical to synthetic TRH. Different brain regions showed high variability in the basal release of TRH (1-20% of tissue content). This suggests the existence of different pools. The response to depolarizing stimulus (56 mM K+) was significant only in the following regions: median eminence, total hypothalamus, preoptic area, nucleus accumbens-lateral septum, amygdala, mesencephalon, medulla oblongata and the cervical region of the spinal cord. These regions have been shown to contain a high number of receptors, a high concentration of TRH nerve endings and are susceptible to TRH effects. These results support the hypothesis that TRH functions as neuromodulator in these areas.

The role of the mediobasal arcuate hypothalamus in relation to opioid systems in the control of ingestive behaviour in the rat

Bilateral, radiofrequency lesions of the mediobasal arcuate hypothalamus (MBH) strongly depleted levels of immunoreactive (ir)-beta-endorphin (beta-EP) in the hypothalamus and other brain tissues: these changes reflect destruction of those beta-EP-containing perikarya which are located in the MBH. No change in plasma ir-beta-EP was seen. The ir-dynorphin (DYN) content of the hypothalamus was also depressed while that of ir-Met-enkephalin was unaffected. The fall in hypothalamic ir-beta-EP was correlated with the fall in that of ir-DYN. Lesioned rats displayed only a minor, transient reduction in rate of weight gain between days 3 and 9 postsurgery: this disappeared thereafter. Further, the lesion did not affect the pattern of weight loss and regain associated with 24 h food and water deprivation. Indeed, the total 24 h (daily) food intake (FI) and water intake (WI) of lesioned rats did not differ from that of sham animals while deprivation-induced hyperphagia and hyperdipsia was not attenuated by the lesions. Moreover, the ability of naltrexone to decrease FI and WI (during both dark and light phases of the daily cycle) was not altered by the lesions. These observations indicate that central beta-EP may not be essential for the maintenance of a normal 24 h FI and WI and that opioid antagonists do not act upon the MBH or upon central beta-EP neurones in their suppression of FI and WI. Further, they suggest that central beta-EP may not fulfil an essential role in the control of body weight in the rat. Lesioned rats did, however, reveal a shift in the diurnal rhythmicity of FI and WI reflected in a reduction in the dark:light ratios of these. An alteration in the diurnal rhythmicity of sleeping and core temperature, but not locomotor activity, was also seen. The shifts in hypothalamic ir-beta-EP and ir-DYN (but no other tissue levels of any peptide) were correlated with the magnitude of the shifts in diurnal rhythmicity of ingestive behaviour. Moreover, lesions caudal to the MBH (not affecting hypothalamic ir-beta-EP or ir-DYN) or dexamethasone treatment (which affects pituitary pools of ir-beta-EP and ir-DYN) did not modify these rhythms. Thus, in these respects, the effects are 'particular' to MBH lesions modifying hypothalamic ir-beta-EP and ir-DYN. The data suggest that the MBH may play a role in the modulation of the diurnal scheduling of ingestive behaviour in the rat.(ABSTRACT TRUNCATED AT 400 WORDS)

Differential effects of amphetamine and related compounds on locomotor activity and metabolic rate in mice

Locomotor activity was measured by photobeam interruptions, and metabolic rate by the production of CO2 (as minute volume expired CO2, or VECO2) in mice. d-Amphetamine (0.3 to 10 mg/kg IP) increased locomotor activity in a dose-dependent manner while suppressing VECO2 over the same 72-min test period, compared to saline-injected controls. This phenomenon of divergent effects on locomotor activity and metabolic rate required central stimulation, as neither ammonium sulfate nor p-hydroxyamphetamine suppressed VECO2. Oxygen consumption was also suppressed by d-amphetamine, indicating that the suppression of VECO2 involved more than a change in respiratory quotient. When baseline activity rates were increased with running wheels, VECO2 and activity were both suppressed by d-amphetamine; VECO2 was suppressed by d-amphetamine more in exercising mice than in sedentary mice. Anorexigenic agents phenmetrazine, aminoxaphen, and fenfluramine, when administered in doses equimolar to maximally effective doses of d-amphetamine, did not consistently affect activity or VECO2. Evidence for mediation of the VECO2 response by corticosterone and endogenous opioid peptides was negative. Further work, with other mediators of the stress response, or with more complete dose-effect studies with anorexigenic compounds, may be necessary to explicate the mechanism of this counter-intuitive divergence of two measures of activity in mice.

Effect of ACTH-like peptides on morphine-induced hypothermia in unrestrained guinea pigs

Peripheral treatment with adrenocorticotropin (1-24) (ACTH1-24), at different doses and sequences, consistently antagonized the decrease in body temperature produced by morphine in the freely moving guinea pig, whereas adrenocorticotropin (4-10) (ACTH4-10), which lacks corticotrophic activity, was partially effective only when it was administered in a high dose 24 h prior to morphine. Centrally administered ACTH1-24 completely prevented the hypothermic effect of intracerebroventricularly (i.c.v.)-injected morphine. Likewise, the i.c.v. administration of ACTH4-10 was equally effective in blocking the i.c.v. morphine-induced hypothermia. Neither ACTH1-24 nor ACTH4-10 did produce changes in body temperature. These results suggest that peripherally administered ACTH1-24 antagonizes indirectly the actions of morphine through the release of adrenal corticosteroids, whereas centrally injected ACTH1-24 or ACTH4-10 act as direct antagonists of morphine effects through opioid receptors.

alpha-Melanocyte-stimulating hormone infused ICV fails to affect body temperature or endotoxin fever in the cat

Permanent cannulae for intracerebroventricular (ICV) infusion were implanted bilaterally in cats following stereotaxic procedures. After colonic temperature was recorded for a one-hour baseline, a 300 microliter ICV infusion was given of CSF control vehicle, 1:100 dilution of W3110 E. coli endotoxin (10(8) organisms/ml) or alpha-melanocyte-stimulating hormone (alpha-MSH) in one of seven doses ranging from 50.0 ng to 50.0 micrograms. Whereas ICV E. coli always induced an intense and prolonged fever of rapid onset, alpha-MSH infused similarly was essentially without effect on the deep body temperature of the normothermic cat. When each of the doses of alpha-MSH was infused ICV, either during the rising phase of an E. coli fever or after the febrile response had reached its asymptote, the core temperature of the cat was unaffected. Similarly, a mixture of E. coli combined with alpha-MSH given ICV failed to alter the characteristics of the rapidly developing fever produced in the cat by this endotoxin. On the other hand, either excess Ca++ ions (50 mM) given ICV or the antipyretic drug. Dipyrone, administered systematically during the course of an endotoxin fever effectively attenuated the animal's elevated body temperature. These results demonstrate that alpha-MSH is apparently neither involved in the central mechanisms underlying normal thermoregulation, nor does it act as an endogenous antipyretic in the cat as has been postulated in another species.

State-dependent effects of beta-endorphin on core temperature in stressed and non-stressed rats

beta-Endorphin, gamma-endorphin, delta-endorphin and morphine injected i.c.v. caused hyperthermia in non-stressed rats; however, the same dose of beta-endorphin and morphine caused hypothermia in stressed animals. These effects of beta-endorphin were antagonized by naloxone. The results suggest that effects of beta-endorphin are different depending on the animal's state and that these effects are mediated via opioid receptors.

Iron deficiency induces reversal of dopamine dependent circadian cycles: differential response to d-amphetamine and TRH

Rats made nutritionally iron-deficient (ID) have significantly diminished haemoglobin, serum iron and hypothermic response to d-amphetamine (15 mg/kg). The reduction of d-amphetamine induced hypothermia is comparatively greater in the dark than in the light period. Neither TRH (1 mg/kg) nor CG 3703, a peptidase resistant TRH analogue (1 mg/kg), induced hypothermia in control of ID animals. However, in combination with d-amphetamine, TRH and CG 3703 did not alter the hypothermic effect observed initially with d-amphetamine. In contrast to control animals, ID rats treated with saline or d-amphetamine (15 mg/kg) exhibited a greater degree of motor activity in the light as compared to the dark period. However, the overall activity (light plus dark) was unchanged in the ID group. The motor activity in response to TRH or CG 3703 was not changed as a result of iron-deficiency. These differential responses may be due to a more pronounced action of d-amphetamine on dopaminergic system, which is known to be changed in iron-deficiency, and of TRH and CG 3703 on the noradrenergic neurones.

Effects of morphine and their antagonism by dexamethasone on body temperature in restrained and unrestrained guinea-pigs

Morphine (M) was administered in different doses intraperitoneally (i.p.) or 50 micrograms intraventriculary (i.c.v.) to restrained and unrestrained guinea-pigs. The systemic administration of M induces a fall in body temperature which is more evident in restrained than in unrestrained guinea-pig. The intraventriculary administration of M produces a fall in body temperature in unrestrained animals, however no significant hypothermic effect was observed in restrained guinea-pig. Dexamethasone antagonized the hypothermic effect observed after the highest dose of M given i.p. The hypothermia observed after the highest dose of M was antagonized by naloxone in all conditions. These findings reemphasize the importance of restraint in determinating the action of M on body temperature and suggest that this effect probably results from stress-related hormone release from the anterior pituitary.

The role of endogenous opiates in thermal regulation of the body during exercise

Naloxone abolished the rise in body temperature seen after bicycle ergometer tests performed by 10 healthy men. This suggests that endogenous opiates play a part in thermal regulation during muscular exercise.

The effects of MIF-I, beta-endorphin and alpha-MSH on d-amphetamine induced paradoxical behavioral thermoregulation: possible involvement of the dopaminergic system

The neuropharmacological basis for d-amphetamine induced paradoxical behavioral thermoregulation remains unclear. This study examined thermoregulatory behavior of rats in a runway device that housed a heat source at one end and in which locomotion along the length of the runway could be observed. Sprague Dawley rats were pretreated with IP injections of saline, beta-endorphin, MIF-1, or alpha-MSH, with a repeat injection after 30 min. In a second experiment, d-amphetamine was administered as the repeat drug for all Ss. The results showed clear differences for heat-source-on vs. heat-source off. All peptides induced hypermotility, although no differentiated effects for the peptides on d-amphetamine induced paradoxical behavioral thermoregulation were found. These findings are discussed in light of the theoretical possibilities that: (a) a ceiling effect exists; (b) there are separate control systems for maintaining body temperature and another for behavioral thermoregulatory responses, and (c) other neurotransmitters may be involved in such induced paradoxical behavioral thermoregulation.

The increased opiate action of beta-endorphin in iron-deficient rats: the possible involvement of dopamine

Rats made nutritionally iron-deficient (ID) have been shown to have a lower brain non-haem. A selective diminution of the binding capacity of the D2-dopaminergic receptors alone was found among nutritionally iron-deficient rats. Peripherally administered beta-endorphin significantly elevated the pain threshold only in the iron-deficient rats. Naloxone blocked the beta-endorphin effect in ID rats. Morphine, as well as haloperidol, elevated the pain threshold in both the iron-deficient and the control rats but significantly more in the former group. No additive effects of combined treatment with beta-endorphin and haloperidol on pain threshold were found. Other neuroleptics also elevated the pain threshold. A possible hypothesis is that dopamine (via beta-endorphin) may play a role in modifying the pain threshold.

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.

Role of beta-endorphin in the control of body temperature in the rabbit

There is evidence of release of the opioid peptide beta-endorphin (beta-E) in the hypothalamus during development of fever and stress-induced hyperthermia. In the unanesthetized rabbit, microinjection of beta-E in the preoptic/anterior hypothalamus (POAH) results in peripheral vasoconstriction, inhibition of evaporative heat loss, and a prolonged elevation of body temperature. These reactions are magnified with increases in ambient temperature. Injections of beta-E nearly abolish vasodilation to back heating and also postural enhancement of heat dissipation ( sprawling , limb extension) in a hot environment. beta-E has also been found to reduce the thermal sensitivity of single POAH neurons to ambient heating. However, POAH beta-E injections do not alter metabolic rate at ambient temperatures from 2 to 27 degrees C, and to this extent beta-E-induced hyperthermia is distinct from fever. It is suggested that beta-E reduces sensitivity of POAH neurons to high ambient temperature and that this reduction leads to increased peripheral vasoconstriction, inhibition of evaporative heat loss, and modification of behavioral thermoregulation resulting in a regulated-type elevation in body temperature. A general neural model is proposed to explain the thermoregulatory effects of beta-E in the rabbit.

Analeptic effects of centrally injected TRH and analogues of TRH in the pentobarbitone-anaesthetized rat

The effect of intracerebral injection of TRH and several biologically stable TRH analogues in the pentobarbitone anaesthetized rat was examined. Bilateral injection of TRH (5.0 micrograms total dose) and the analogues RX 77368 (0.01-1.0 microgram), CG 3509 (0.1-1.0 microgram), DN-1417 (1.0 microgram) and MK-771 (1.0 microgram) into the nucleus accumbens reduced the pentobarbitone-induced sleeping time. The TRH metabolite DKP (5 micrograms) had no effect on the sleeping time following intra-accumbens injection. Intra-septal injection of TRH (1.0-5.0 micrograms), RX 77368 (0.1-1.0 microgram) and CG 3509 (0.1-1.0 microgram) also reversed the pentobarbitone-induced sleeping time. In contrast, TRH (5 micrograms) injected into the striatum had no effect on the pentobarbitone-induced sleeping time, and CG 3509 (0.1 microgram) and RX 77368 (0.1 microgram) had weaker effects following intrastriatal injection compared to injection of these analogues into the nucleus accumbens and septum. Measurements of core temperature and respiration rate in rats following intra-accumbens or septal injection of TRH, CG 3509 and RX 77368 showed these peptides to reverse pentobarbitone-induced hypothermia and stimulate respiration rate. However, while intrastriatal injections of CG 3509 and RX 77368 caused an increase in respiration rate they had no effect on core temperature. These results suggest a close association between peptide-induced respiratory stimulation and reversal of pentobarbitone-induced anaesthesia. Since intra-accumbens and septal injection of dopamine (20-100 micrograms) failed to reverse anaesthesia, it is unlikely that the peptide-induced responses are mediated via dopamine release.

Reduced thermal sensitivity in the rabbit by beta-endorphin injection into the preoptic/anterior hypothalamus

Male New Zealand White rabbits, Oryctolagus cuniculus, were stereotaxically implanted with a guide tube above the preoptic/anterior hypothalamus (PO/AH) for the injection of beta-endorphin (beta-E) or saline at ambient temperatures of 20 and 25 degrees C. Ear skin and PO/AH temperatures were recorded in loosely restrained control and beta-E-pretreated rabbits while radiant heat was applied to the dorsal skin. Without beta-E administration the ear skin temperature (Tear) underwent a rapid increase during back heating. Following beta-E administration there was a marked vasoconstriction along with a large reduction in responsiveness of ear skin temperature to radiant heat. The time to respond to radiant heat for beta-E-pretreated rabbits was significantly longer than that for control rabbits. In control animals, the increase in Tear in response to radiant heat exposure depended upon the initial ear temperatures. However, in beta-E-pretreated rabbits vasodilatation response to radiant heat exposure was nearly the same regardless of the initial Tear. These data suggest that there is a significant reduction in passage of temperature information from cutaneous thermal receptors to the PO/AH in beta-E-pretreated animals and that beta-E-induced reduction in sensitivity of the vasomotor system to radiant heat may account for the effectiveness of this opioid peptide to promote hyperthermia in the rabbit.

Opiates influence behavioral thermoregulation in the curly-tailed lizard, Leiocephalus carinatus

Low doses of the opioid agonist, morphine (1-3 mg kg-1), significantly increased the behaviorally selected body temperatures of the curly-tailed lizard, Leiocephalus carinatus. A higher dose of morphine (10 mg kg-1) resulted in an initial behavioral hyperthermia that was followed by a significant decrease in preferred temperatures and a subsequent behavioral hypothermia which declined to control levels within 3-4 hr. These effects could be blocked and reversed by the opiate antagonist, naloxone, with naloxone (1 and 10 mg kg-1) by itself causing significant dose-dependent decreases in preferred temperatures. These morphine and naloxone induced changes occurred regardless of initial body temperatures. These results suggest that opiates are involved in the control of behavioral thermoregulation in lizards.

Changes in circadian rhythms of thermoregulation and motor activity in rats as a function of aging: effects of d-amphetamine and alpha-MSH

Thermoregulatory and motor activity circadian cycles are age-dependent. While the level of thermoregulation and motor activity remained almost at the same level during the first 1-15 months during the light portion of the 24-hr cycle, a significant decrease in the level of both rhythms was observed during the dark period. Therefore, older rats exhibited reversed cycles compared with younger rats. Treatments with d-amphetamine resulted in the enhancement of reversal of the cycles. Rats treated with alpha-MSH failed to exhibit a reversal of the cycles. While the effects of d-amphetamine are mediated by the brain DA mesolimbic pathway, it seems that alpha-MSH acts on the dopaminergic system at different sites of action.

Opiate regulation of maternal behavior in the rat

The effects of the opiate agonist morphine, the opiate antagonist naloxone and the weak opiate nonanalgesic dextrorphan on the expression of maternal behavior were investigated in a series of three experiments. In the first experiment treatment of rats with morphine (5 mg/kg, subcutaneously) after ovariectomy and hysterectomy on day 17 of gestation resulted in a disruption in the onset and quality of maternal responsiveness in the homecage and in a T-maze test. The duration of morphine's acute disruptive action was 2-4 hours. In the second experiment concurrent treatment of morphine-injected rats with naloxone prevented the disruptive effects of morphine in both the homecage and T-maze tests. The effects of morphine did not appear to result from a severe alteration in activity levels as measured in an open-field test, although morphine did increase activity slightly by the fifth day of treatment. In the third experiment treatment of rats after ovariectomy plus hysterectomy on day 17 of gestation with dextrorphan failed to disrupt maternal behavior. These results indicate that morphine disrupts maternal behavior through an opiate receptor mechanism, and suggests to us that endogenous opiates may mediate the expression of maternal behavior under certain physiological conditions.

Behavioral effects of melanocyte stimulating hormone release-inhibiting factor-1 (MIF-1)

Consideration of the isolation, structure, localization, and behavioral effects of melanocyte stimulating hormone release inhibiting factor (MIF-1) is followed by a review of its opiate antagonistic and clinical effects. Evidence pertaining to various hypotheses offered in explanation of these behavioral effects is examined and evaluated. It is concluded that MIF-1 affects behavior in many instances with possible antagonistic effects as well as clinical possibilities.

Central effects of neuropeptides on ventilation in the rat

We have examined the effects of centrally applied neuropeptides on ventilation (respiratory rate, tidal volume, and minute ventilation) in urethane-anesthetized rats. TRH caused an increase in respiratory rate, a decrease in tidal volume, but an increase in net minute ventilation. One TRH metabolite, acid TRH, caused similar changes, but no effect was observed from the other TRH metabolite, cHis-Pro. Both bombesin and calcitonin caused increases in minute ventilation due to increases in respiratory rate and tidal volume. Additionally, bombesin induced periodic sighing respirations at rates up to 15/minute which was observed with no other neuropeptide. Substance P, somatostatin, and neurotensin had no effect upon ventilation variables.

A review of terms for regulated vs. forced, neurochemical-induced changes in body temperature

Deviations of the body temperature of homeothermic animals may be regulated or forced. A regulated change in core temperature is caused by a natural or synthetic compound that displaces the set-point temperature. A forced shift occurs when an excessive environmental or endogenous heat load, or heat sink, exceeds the body's capacity to thermoregulate but does not affect set-point. A fever is the paradigm of a regulated increase in body temperature, but the term fever has acquired a strict pathological definition over the past two decades. Consequently, other forms of nonpathological, regulated elevations in body temperature have generally been classified as hyperthermia; and decreases in core temperature--either forced or regulated--have generally been classified as hypothermia. Since the terms hyperthermia and hypothermia fail to distinguish a regulated vs. a forced temperature change, a confusion of terms has been created in the literature. It would appear that "resisted or unregulated hyperthermia" and "hypothermia," respectively, are appropriate terms for describing a forced increase and decrease in core temperature. A nonpathological but regulated elevation in temperature may be defined as unresisted or regulated hyperthermia, whereas a regulated decrease in temperature may be termed unresisted or regulated hypothermia. This simple scheme appears to be the most practical means for distinguishing between forced and regulated changes in core temperature.

The role of the ventral noradrenergic bundle in relation to endorphins in the control of core temperature, open-field and ingestive behaviour in the rat

Discrete, bilateral, radiofrequency destruction of the ventral noradrenergic bundle (VB) resulted in a pronounced fall in levels of noradrenaline in the hypothalamus but not in the cortex. On days 4 and 12, but not 28, post-surgery, VB-lesioned rats were hyperactive (rearing and ambulation) upon exposure to a novel open-field space. This hyperactivity was greatly attenuated by naloxone, which did not significantly modify sham activity. These data suggest that the VB may be involved in the control of locomotor-exploratory activity via an interaction with an endorphinergic system. On day 4, but not 12 or 25, VB-lesioned rats displayed a significant elevation in core temperature (Tc). No difference in the hyperthermia elicited by introduction into the open-field was, however, seen between VB-lesioned and sham rats on day 4. In both groups, this rise in Tc was strongly attenuated by naloxone. These data indicate that the VB may be involved in the control of Tc but that it does not mediate novelty-stress evoked hyperthermia, for which endorphins are primarily responsible. Within 7 days post-surgery, VB-lesioned rats developed an enhancement of daily food intake which led to a slight obesity. From day 15 onward, a hyperdipsia was also seen in VB-lesioned rats. Naltrexone reduced the food and water intake of both sham and VB-lesioned animals but failed to totally block this hyperphagia. It is suggested that the VB is involved in the regulation of daily ingestive behaviour and that endorphins do not exclusively mediate the VB-lesion induced hyperphagia.