Hypothalamic opioids and the acute-phase glycoprotein response in guinea pigs

Physiology of temperature regulation: comparative aspects

Few environmental factors have a larger influence on animal energetics than temperature, a fact that makes thermoregulation a very important process for survival. In general, endothermic species, i.e., mammals and birds, maintain a constant body temperature (Tb) in fluctuating environmental temperatures using autonomic and behavioural mechanisms. Most of the knowledge on thermoregulatory physiology has emerged from studies using mammalian species, particularly rats. However, studies with all vertebrate groups are essential for a more complete understanding of the mechanisms involved in the regulation of Tb. Ectothermic vertebrates-fish, amphibians and reptiles-thermoregulate essentially by behavioural mechanisms. With few exceptions, both endotherms and ectotherms develop fever (a regulated increase in Tb) in response to exogenous pyrogens, and regulated hypothermia (anapyrexia) in response to hypoxia. This review focuses on the mechanisms, particularly neuromediators and regions in the central nervous system, involved in thermoregulation in vertebrates, in conditions of euthermia, fever and anapyrexia.

Unresponsiveness of mu-opioid receptor knockout mice to lipopolysaccharide-induced fever

Recently, we demonstrated that lipopolysaccharide (LPS)-induced fever could be suppressed by a selective mu-opioid receptor antagonist, indicating that the mu-opioid system is involved in the LPS fever. In the present study, to confirm the role of the mu-opioid system in the pathogenesis of LPS fever, we used mice lacking the mu-opioid receptor. In the wild type (WT), following intraperitoneal (i.p.) injection of 100 microg kg(-1) of LPS, body temperature (T(b)) increased approximately 1 degrees C and remained elevated during the 360-min recording period. In the mu-opioid receptor knockout (MOR-KO) mice, the administration of 100 microg kg(-1) i.p. of LPS did not induce fever during the recording period. Saline by itself, given i.p., did not alter the T(b), either in WT or MOR-KO. These results confirm that the mu-opioid system is involved in LPS-induced fever.

CO2 production during acute infection in malnourished Malawian children

OBJECTIVE

This study tested the hypotheses that the rate of CO2 production is less in marasmic children with acute infection when compared to well-nourished children, but greater when compared to uninfected marasmic children.

DESIGN

A descriptive comparison of children aged 12-60 months who had their rates of CO2 production measured using a stable isotope tracer dilution method while receiving feedings. Body mass index (BMI) was the best measure of lean body mass available in this study.

SETTING

Queen Elizabeth Central Hospital, Blantyre, Malawi.

SUBJECTS

A total of 56 children were studied, 28 with marasmus and acute infection, 16 with marasmus, and 12 well nourished with acute infection. Those with acute infection had malaria, pneumonia, or sepsis.

RESULTS

Well-nourished children with acute infection produced more CO2 than marasmic children (344+/-60 vs 225+/-65 mmol CO2/h, mean+/-s.d., P<0.001; 24.2+/-4.6 vs 18.4+/-5.4 mmol CO2/BMI h, P=0.001). However, the rate of CO2 production in marasmic children with acute infection was not greater than in uninfected marasmic children (225+/-65 vs 228+/-61 mmol CO2/h). The observed rate of CO2 production was greater than that which could be produced from the dietary intake alone (29.6 vs. 25.8 mmol CO2/kg h).

CONCLUSIONS

Marasmic children do not increase energy expenditure in response to acute infection, as well-nourished children do. Dietary energy provided to marasmic children should be at least 420 kJ/kg day.

Blockade of lipopolysaccharide-induced fever by a mu-opioid receptor-selective antagonist in rats

The endogenous opioid system has been found to be involved in fever caused by pyrogens. In the present study, we have investigated the role of the mu-opioid receptor in the brain in fever induced by lipopolysaccharide. Rats were microinjected with 1 microg of the mu-opioid receptor-selective antagonist, cyclic D-Phe-Cys-Tyr-D-Trp-Arg-Thr-Pen-Thr-NH(2) (CTAP), into the preoptic anterior hypothalamus. Thirty minutes later, lipopolysaccharide (50 microg/kg) was injected intraperitoneally (i.p.). CTAP reduced by 1 degrees C the fever induced by lipopolysaccharide. However, it did not affect lipopolysaccharide fever when it was given 3 h after lipopolysaccharide injection. These data indicate that mu-opioid receptors within the preoptic anterior hypothalamus mediate the initiation of lipopolysaccharide fever and suggest that the opioid system is involved in the pathogenesis of fever in rats.

Prospects and advances in hormonal immunomodulatory therapy

Modulation of the immune network through the hormonal system is an exciting emerging concept. It results from a decade of experimental research obtained on rodents. Unfortunately, the therapeutic response on NZB/NZW F1 mice with murine lupus or in adjuvant induced arthritis are not transferable to man. This new field opens new therapeutic perspectives with well known and relatively safe drugs (hormone agonists, antagonists or inhibitors of hormonal secretion). Today we lack controlled, randomized clinical studies, with long-term follow-up. We also need to identify the subgroup of patients who could benefit from hormonal immunomodulation (sex, basal hormonal status, menopausal status for women, disease activity).

Naloxone suppresses the rising phase of fever induced by interferon-alpha

Interferon-alpha (IFN-alpha, 2.0 x 10(4) units) was bilaterally microinjected into the medial preoptic area and anterior hypothalamus in conscious rats treated 10 min prior with an opioid receptor antagonist, naloxone (NLX, 2 mg/kg, IM) or a prostaglandin synthetase inhibitor, acetaminophen (ACAP, 25 mg/kg, IM). The IFN-alpha-induced rise of rectal temperature (Tre) was suppressed from 20 to 60 min in NLX pretreated rats and from 30 to 180 min in ACAP pretreated rats. The rate of rise in Tre during the initial 20 min observed in NLX pretreated rats was significantly smaller than that in ACAP or saline pretreated rats. ACAP suppressed the fever when it was given 50 or 100 min after injection of IFN-alpha. In contrast, NLX did not affect the fever when given 25 or 50 min after IFN-alpha. The results suggest that an opioid that its involvement may last only in the early phase of the fever, but not after the plateau has been reached.

Neuromodulation of fever: apparent involvement of opioids

It was recently reported that the opiate antagonist, naloxone (Nal), blocks the changes induced by the endogenous pyrogen, interferon-alpha 2 (IFN), in the electrical activity of hypothalamic thermosensitive neurons in rat brain slice preparations. This study was undertaken to determine whether the pyrogenic response to this cytokine might, therefore, be modulated through Nal-reversible opiate receptors. To examine this possibility, conscious guinea pigs were injected IV with recombinant human (rh) IFN (10 MU/animal), or, for comparison, with S. enteritidis endotoxin (lipopolysaccharide, LPS; 2 micrograms/kg), rh tumor necrosis factor-alpha (TNF; 20 micrograms/kg), or rh interleukin-6 (IL6; 50 micrograms/kg); Nal (10 mg/kg, SC) was administered immediately before the pyrogens. And also for comparison, in separate experiments, indomethacin (Indo; 10 mg/kg, IM) was injected 20 min before the pyrogens. Both Nal and Indo abolished the febrile rises evoked by IFN, TNF, and IL6. Nal reduced the first and suppressed the second of the characteristically bimodal febrile response to LPS; Indo depressed both peaks. Neither blocker had any significant thermal effect by itself. These results suggest that two processes may mediate the pyrogenic effects of these substances, viz., an endogenous opioid- and a PGE-dependent mechanism.

Actions of interferon alpha and interleukin- 1 beta on the glucose-responsive neurons in the ventromedial hypothalamus

Effects of recombinant interferon alpha (rhIFN alpha) and interleukin-1 beta (rhIL-1 beta) on the activity of glucose-responsive and glucose-unresponsive neurons in the ventromedial hypothalamus (VMH) were investigated with rat tissue slice preparations. While the majority of neurons which increased the activity in response to a rise in glucose concentration were excited by perfusion of rhIFN alpha (100-5000 U/ml) and rhIL-1 beta (40-160 ng/ml), most of the neurons which increased their activity to a fall in glucose concentration were inhibited by rhIFN beta. The majority of glucose-unresponsive neurons were not affected by the cytokines. These neuronal responses are appropriate in explaining the anorexia induced by IFN alpha and IL-1. Concurrent application of sodium salicylate, an inhibitor of prostaglandin synthesis, blocked both the increase and decrease in activities of VMH neurons by rhIL-1 beta, but not those by rhIFN alpha. Alpha-melanocyte stimulating hormone (alpha-MSH) (8 x 10(-9)-6.4 x 10(-7) M), an endogenous antipyretics and a possible antagonist of IL-1 at lymphocytes, specifically depressed the responses to rhIL-1 beta, but not those to rhIFN alpha. As has been previously shown in preoptic and anterior hypothalamic neurons, naloxone could block the responses of VMH neurons to rhIFN alpha, suggesting the opioid receptor mediation of IFN alpha's actions on the VMH neurons.

Recombinant human interleukin-1 beta alters the activity of preoptic thermosensitive neurons in vitro

Effects of recombinant human interleukin-1 beta (rhIL-1 beta) on the single activity of thermosensitive and thermally insensitive neurons in the preoptic and anterior hypothalamus (PO/AH) were investigated in the rat's brain tissue slices. RhIL-1 beta (2.8 X 10(-9)-1.2 X 10(-8) M) decreased the activity in 19 of 27 warm-sensitive neurons and excited 2 of 3 cold-sensitive neurons, but had no effect on the majority (22 of 32) of thermally insensitive neurons. The neuronal responses to local rhIL-1 beta could be observed in a Ca2+ free/high Mg2+ solution, suggesting the postsynaptic actions of rhIL-1 beta. The actions of rhIL-1 beta on thermosensitive neurons were blocked or attenuated by concurrent application of sodium salicylate, but not by naloxone. The results suggest that centrally formed IL-1 beta may induce fever by its actions on PO/AH thermosensitive neurons, which do not involve the opioid receptor mechanisms.

Interleukin-1 interaction with neuroregulatory systems: selective enhancement by recombinant human and mouse interleukin-1 of in vitro opioid peptide receptor binding in rat brain

Interleukin-1 (IL-1) exerts a wide variety of biological effects on various cell types and may be regarded as a pleiotropic peptide hormone. Biological evidence suggests that IL-1 participates in the modulation of central nervous system physiology and behaviour in a fashion characteristic of neuroendocrine hormones. In this investigation, recombinant (r) human (h) IL-1 and r mouse (m) IL-1 were examined for their modulation of opioid peptide receptor binding in vitro. Experiments were performed on frozen sections of rat brain. Receptor binding of radiolabeled substance P and of radiolabeled neurotensin were not significantly affected by the presence of rIL-1s. Recombinant IL-1s, however, significantly enhanced specific binding of 125I-beta-endorphin (125I-beta-END) and of D-ala2-(tyrosyl-3,5-3H)enkephalin-(5-D-leucine) (3H-D-ALA), equipotently and in a concentration-dependent manner with maximal activity occurring at a concentration of 10 LAF units/ml. The increased binding of 125I-beta-END and 3H-D-ALA was blocked steroselectively by (-)-naloxone and by etorphine, suggesting detection of opiate receptors. In addition, brain distribution patterns of receptors labeled in the presence of rIL-1s corresponded to patterns previously published for opiate receptors. Autoradiographic visualization of receptors revealed that rIL-1s in the different areas of the brain exert their effect on opioid binding with comparable potencies. The data suggest that certain central nervous system effects of IL-1s may be mediated by their selective interaction with opiatergic systems at the receptor level.(ABSTRACT TRUNCATED AT 250 WORDS)

Neural mechanisms in the pyrogenic and acute-phase responses to interleukin-1

It has become increasingly apparent over the past several decades that the hypothalamus, among other brain regions, plays an important part in the modulation of the immune system (reviewed in Korneva et al., 1985; Roszman & Brooks, 1985; Jankovic & Spector, 1986; Cotman et al., 1987). Since the hypothalamus also mediates the fever and various other acute-phase responses characteristic of the early stages of infection (reviewed in Hellon & Townsend, 1983; Blatteis, 1984, 1985; Cooper, 1987), it is possible that the localization within a common brain region of the controllers of several, different host defense reactions is not a happenstance, but represents a highly organized neuronal network serving to coordinate them. Indeed, pyrogenic, inflammatory, and immune responses do interact in the defense of the host against infection (reviewed in Dinarello, 1984). It is not yet known how immune responses are integrated centrally, but some data are available on the neural mechanisms controlling fever and certain components of the acute-phase reaction. The purpose of this paper is to review these briefly in the hope that a background can be provided against which features that may be common to neuroimmunomodulation and to the control of acute-phase reactions might be revealed.

Neuroimmune intercommunication, central opioids, and the immune response to bacterial endotoxin

Muramyl dipeptide is the smallest biologically active fragment of the lipopolysaccharide (LPS) moiety of gram-negative bacteria cell walls. The present report demonstrates that this product, associated with the immune response to bacterial infection, can modify CNS activity. Specifically, it is demonstrated that 6-0-stearoyl-muramyl dipeptide (MDP) can attenuate opiate withdrawal severity in a dose-dependent fashion when injected directly into areas of the brain essential for this phenomenon. In addition, MDP alters both baseline and postnarcotic electrophysiologic responses of four brain areas essential for various opioid activities. Similar findings have been reported for interferon-alpha (IFN-alpha), a peptide associated with the immune response to virus. Yet, even though MDP and IFN are shown to exert similar effects on opioid activity, there are also some very distinct differences in the actions of both of these immune response products. These observations suggest that central opioid systems may provide targets for the perception as well as the differentiation of afferent immunologic sensory input to the brain.

Immune response products alter CNS activity: interferon modulates central opioid functions

The present report provides evidence to support the hypothesis that peptides released during an immune response alter CNS activity and thus may provide a means for the immune system to transmit afferent signals into the brain. Specifically, it is demonstrated that recombinant interferon-alpha (rIFN-alpha), a peptide associated with the immune response to viral infection, can alter opiate withdrawal severity in a dose-dependent manner upon direct injection into brain areas essential for this phenomenon. These results are compared and contrasted with the effect of systemically injected rIFN-alpha upon opiate withdrawal. In addition, an electrophysiological investigation into the basis of the interaction of opioids and rIFN-alpha in brain structures essential for the expression of opioid activities is also presented. Finally, the effects of rIFN-alpha upon the functions of both the CNS and other systems is discussed in terms of the effects reported for other peptides associated with immune responses.

Evidence of an immune system to brain communication axis that affects central opioid functions: muramyl peptides attenuate opiate withdrawal

Muramyl peptides are metabolic breakdown products of bacterial cell walls formed in vivo by the reticuloendothelial system. These agents have a variety of immune modulatory and neuropharmacologic effects. It has previously been demonstrated that a variety of immune modifying agents can induce alterations in certain behaviors elicited by opiates. In the present study we investigate possible reciprocal interactions between muramyl dipeptides (MDPs) and central opioid systems using three different experimental models: (1) naloxone-precipitated withdrawal behavior in morphine-dependent rats; (2) the tail immersion assay for determination of morphine-induced antinociception and (3) rectal temperature measurement of the pyrogenic activity of MDP. It is shown that two derivatives of MDP attenuate the severity of naloxone-precipitated withdrawal and morphine-induced antinociception. In addition, it is demonstrated that the pyrogenic activity of a stearoyl derivative of MDP is altered by chronic morphine treatment. These findings suggest both novel neuropharmacologic properties of muramyl dipeptides, as well as demonstrate that yet another immune modifier interacts with centrally mediated opioid phenomena.

Changes in body temperature after administration of antipyretics, LSD, delta 9-THC and related agents: II

Antipyretics, in particular acetaminophen, aspirin and ibuprofen, constitute the single most important class of drugs used therapeutically for an effect on body temperature. Hallucinogens exert prominent actions on the central nervous system, and it is not surprising that, like so many other centrally-acting agents, they too often affect temperature. This compilation primarily covers the considerable amount of data published from 1981 through 1985 on the interactions of these drugs and thermoregulation, but data from many earlier papers not included in a previous compilation are also tabulated. The effects of agents not classically considered as antipyretics on temperatures of febrile subjects are also covered. 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 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.

The effect of alpha-interferon, cyclosporine A, and radiation-induced immune suppression on morphine-induced hypothermia and tolerance

An interconnection between the immune and the central nervous systems has been suggested by investigators studying the actions of several types of immune modifying agents and procedures upon opiate related phenomena. These studies have included the effects of altering immune system function by administration of either alpha-interferon, cyclosporine or radiation exposure upon naloxone-precipitated opiate withdrawal and upon opioid antinociceptive effects. The present study extends these earlier investigations by examining the effect of immune modulation upon opiate induced hypothermia. The results demonstrate that interferon and cyclosporine have no effects on baseline temperature or morphine induced hypothermia, while irradiation exposure elicits hyperthermia without affecting morphine-induced hypothermia. Finally, neither cyclosporine nor irradiation affect the development of tolerance to morphine induced hypothermia, while a single injection of the immune system modifier interferon was able to prevent the development of such tolerance. These observations suggest that yet another opiate-related phenomenon may be regulated at least in part by the immune system. These results together with our previous findings are further evidence of a link between the immune system and the CNS mediated through the opioid system. In addition, these studies further support our earlier hypothesis that "Interferon" is one of the endogenous substances which serves to prevent the development of tolerance and dependence to endogenous opioids.

Opiate antinociception is altered by immunemodification: the effect of interferon, cyclosporine and radiation-induced immune suppression upon acute and long-term morphine activity

It has recently been demonstrated that various forms of immune modification result in a profound attenuation of the opiate withdrawal syndrome. Herein we investigate the extent to which some of the immune modifiers active in withdrawal attenuation affect other opiate related behaviors, namely antinociception and the development of tolerance to this effect. The observations demonstrate that immune modification by cyclosporine and irradiation exposure result in an alteration of the acute antinociceptive effect of morphine; while none of these treatments modify the development of tolerance to this property of morphine.