Stimulation of vasopressin release in the ventral septum of the rat brain suppresses prostaglandin E1 fever

Activation of Preoptic Arginine Vasopressin Neurons Induces Hyperthermia in Male Mice

Arginine vasopressin (AVP) is a neuropeptide acting as a neuromodulator in the brain and plays multiple roles, including a thermoregulatory one. However, the cellular mechanisms of action are not fully understood. Carried out are patch clamp recordings and calcium imaging combined with pharmacological tools and single-cell RT-PCR to dissect the signaling mechanisms activated by AVP. Optogenetics combined with patch-clamp recordings were used to determine the neurochemical nature of these neurons. Also used is telemetry combined with chemogenetics to study the effect of activation of AVP neurons in thermoregulatory mechanisms. This article reports that AVP neurons in the medial preoptic (MPO) area release GABA and display thermosensitive firing activity. Their optogenetic stimulation results in a decrease of the firing rates of MPO pituitary adenylate cyclase-activating polypeptide (PACAP) neurons. Local application of AVP potently modulates the synaptic inputs of PACAP neurons, by activating neuronal AVPr1a receptors and astrocytic AVPr1b receptors. Chemogenetic activation of MPO AVP neurons induces hyperthermia. Chemogenetic activation of all AVP neurons in the brain similarly induces hyperthermia and, in addition, decreases the endotoxin activated fever as well as the stress-induced hyperthermia.

Sexually dimorphic role of BNST vasopressin cells in sickness and social behavior in male and female mice

Circumstantial evidence supports the hypothesis that the sexually dimorphic vasopressin (AVP) innervation of the brain tempers sickness behavior in males. Here we test this hypothesis directly, by comparing sickness behavior in animals with or without ablations of BNST AVP cells, a major source of sexually dimorphic AVP in the brain. We treated male and female AVP-iCre+ and AVP-iCre- mice that had been injected with viral Cre-dependent caspase-3 executioner construct into the BNST with lipopolysaccharide (LPS) or sterile saline, followed by behavioral analysis. In all groups, LPS treatment reliably reduced motor behavior, increased anxiety-related behavior, and reduced sucrose preference and consumption. Male mice, whose BNST AVP cells had been ablated (AVP-iCre+), displayed only minor reductions in LPS-induced sickness behavior, whereas their female counterparts displayed, if anything, an increase in sickness behaviors. All saline-treated mice with BNST AVP cell ablations consumed more sucrose than did control mice, and males, but not females, with BNST AVP cell ablations showed reduced preference for novel conspecifics compared to control mice. These data confirm that BNST AVP cells control social behavior in a sexually dimorphic way, but do not play a critical role in altering sickness behavior.

From adolescence to late aging: A comprehensive review of social behavior, alcohol, and neuroinflammation across the lifespan

The passage of time dictates the pace at which humans and other organisms age but falls short of providing a complete portrait of how environmental, lifestyle and underlying biological processes contribute to senescence. Two fundamental features of the human experience that change dramatically across the lifespan include social interactions and, for many, patterns of alcohol consumption. Rodent models show great utility for understanding complex interactions among aging, social behavior and alcohol use and abuse, yet little is known about the neural changes in late aging that contribute to the natural decline in social behavior. Here, we posit that aging-related neuroinflammation contributes to the insipid loss of social motivation across the lifespan, an effect that is exacerbated by patterns of repeated alcohol consumption observed in many individuals. We provide a comprehensive review of (i) neural substrates crucial for the expression of social behavior under non-pathological conditions; (ii) unique developmental/lifespan vulnerabilities that may contribute to the divergent effects of low-and high-dose alcohol exposure; and (iii) aging-associated changes in neuroinflammation that may sit at the intersection between social processes and alcohol exposure. In doing so, we provide an overview of correspondence between lifespan/developmental periods between common rodent models and humans, give careful consideration to model systems used to aptly probe social behavior, identify points of coherence between human and animal models, and point toward a multitude of unresolved issues that should be addressed in future studies. Together, the combination of low-dose and high-dose alcohol effects serve to disrupt the normal development and maintenance of social relationships, which are critical for both healthy aging and quality of life across the lifespan. Thus, a more complete understanding of neural systems-including neuroinflammatory processes-which contribute to alcohol-induced changes in social behavior will provide novel opportunities and targets for promoting healthy aging.

Detection of activity-dependent vasopressin release from neuronal dendrites and axon terminals using sniffer cells

Our understanding of neuropeptide function within neural networks would be improved by methods allowing dynamic detection of peptide release in living tissue. We examined the usefulness of sniffer cells as biosensors to detect endogenous vasopressin (VP) release in rat hypothalamic slices and from isolated neurohypophyses. Human embryonic kidney cells were transfected to express the human V1a VP receptor (V1aR) and the genetically encoded calcium indicator GCaMP6m. The V1aR couples to Gq₁₁, thus VP binding to this receptor causes an increase in intracellular [Ca²⁺] that can be detected by a rise in GCaMP6 fluorescence. Dose-response analysis showed that VP sniffer cells report ambient VP levels >10 pM (EC₅₀ = 2.6 nM), and this effect could be inhibited by the V1aR antagonist SR 49059. When placed over a coverslip coated with sniffer cells, electrical stimulation of the neurohypophysis provoked a reversible, reproducible, and dose-dependent increase in VP release using as few as 60 pulses delivered at 3 Hz. Suspended sniffer cells gently plated over a slice adhered to the preparation and allowed visualization of VP release in discrete regions. Electrical stimulation of VP neurons in the suprachiasmatic nucleus caused significant local release as well as VP secretion in distant target sites. Finally, action potentials evoked in a single magnocellular neurosecretory cell in the supraoptic nucleus provoked significant VP release from the somatodendritic compartment of the neuron. These results indicate that sniffer cells can be used for the study of VP secretion from various compartments of neurons in living tissue. NEW & NOTEWORTHY The specific functional roles of neuropeptides in neuronal networks are poorly understood due to the absence of methods allowing their real-time detection in living tissue. Here, we show that cultured "sniffer cells" can be engineered to detect endogenous release of vasopressin as an increase in fluorescence.

The Oxytocin Receptor: From Intracellular Signaling to Behavior

The many facets of the oxytocin (OXT) system of the brain and periphery elicited nearly 25,000 publications since 1930 (see FIGURE 1 , as listed in PubMed), which revealed central roles for OXT and its receptor (OXTR) in reproduction, and social and emotional behaviors in animal and human studies focusing on mental and physical health and disease. In this review, we discuss the mechanisms of OXT expression and release, expression and binding of the OXTR in brain and periphery, OXTR-coupled signaling cascades, and their involvement in behavioral outcomes to assemble a comprehensive picture of the central and peripheral OXT system. Traditionally known for its role in milk let-down and uterine contraction during labor, OXT also has implications in physiological, and also behavioral, aspects of reproduction, such as sexual and maternal behaviors and pair bonding, but also anxiety, trust, sociability, food intake, or even drug abuse. The many facets of OXT are, on a molecular basis, brought about by a single receptor. The OXTR, a 7-transmembrane G protein-coupled receptor capable of binding to either Gαior Gαqproteins, activates a set of signaling cascades, such as the MAPK, PKC, PLC, or CaMK pathways, which converge on transcription factors like CREB or MEF-2. The cellular response to OXT includes regulation of neurite outgrowth, cellular viability, and increased survival. OXTergic projections in the brain represent anxiety and stress-regulating circuits connecting the paraventricular nucleus of the hypothalamus, amygdala, bed nucleus of the stria terminalis, or the medial prefrontal cortex. Which OXT-induced patterns finally alter the behavior of an animal or a human being is still poorly understood, and studying those OXTR-coupled signaling cascades is one initial step toward a better understanding of the molecular background of those behavioral effects.

Mechanisms of fever production and lysis: lessons from experimental LPS fever

Fever is a cardinal symptom of infectious or inflammatory insults, but it can also arise from noninfectious causes. The fever-inducing agent that has been used most frequently in experimental studies designed to characterize the physiological, immunological and neuroendocrine processes and to identify the neuronal circuits that underlie the manifestation of the febrile response is lipopolysaccharide (LPS). Our knowledge of the mechanisms of fever production and lysis is largely based on this model. Fever is usually initiated in the periphery of the challenged host by the immediate activation of the innate immune system by LPS, specifically of the complement (C) cascade and Toll-like receptors. The first results in the immediate generation of the C component C5a and the subsequent rapid production of prostaglandin E2 (PGE2). The second, occurring after some delay, induces the further production of PGE2 by induction of its synthesizing enzymes and transcription and translation of proinflammatory cytokines. The Kupffer cells (Kc) of the liver seem to be essential for these initial processes. The subsequent transfer of the pyrogenic message from the periphery to the brain is achieved by neuronal and humoral mechanisms. These pathways subserve the genesis of early (neuronal signals) and late (humoral signals) phases of the characteristically biphasic febrile response to LPS. During the course of fever, counterinflammatory factors, "endogenous antipyretics," are elaborated peripherally and centrally to limit fever in strength and duration. The multiple interacting pro- and antipyretic signals and their mechanistic effects that underlie endotoxic fever are the subjects of this review.

Central and peripheral neuroimmune responses: hyporesponsiveness during pregnancy

There are periods in the life of a healthy animal (including humans) when the febrile response to an immune challenge is suppressed. One such period is during late pregnancy, particularly around the time of parturition. In the 30 or so years since this 'febrile hyporesponsiveness' was first noted, much work has been done to investigate the mechanisms and adaptive significance of this phenomenon. In this review we present some insight into how and why the body deliberately re-programmes itself to develop smaller fevers in response to an immune challenge and therefore to be potentially less successful at fighting infection.

Effects of electrical stimulation of ventral septal area on firing rates of pyrogen-treated thermosensitive neurons in preoptic anterior hypothalamus from rabbits

Although there is considerable evidence supporting that fever evolved as a host defense response, it is important that the rise in body temperature would not be too high. Many endogenous cryogens or antipyretics that limit the rise in body temperature have been identified. Endogenous antipyretics attenuate fever by influencing the thermoregulatory neurons in the preoptic anterior hypothalamus (POAH) and in adjacent septal areas including ventral septal area (VSA). Our previous study showed that intracerebroventricular (I.C.V.) injection of interleukin-1beta (IL-1beta) affected electrophysiological activities of thermosensitive neurons in VSA regions, and electrical stimulation of POAH reversed the effect of IL-1beta. To further investigate the functional electrophysiological connection between POAH and VSA and its mechanisms in thermoregulation, the firing rates of thermosensitive neurons in POAH of forty-seven unit discharge were recorded by using extracellular microelectrode technique in New Zealand white rabbits. Our results show that the firing rates of the warm-sensitive neurons decreased significantly and those of the cold-sensitive neurons increased in POAH when the pyrogen (IL-1beta) was injected I.C.V. The effects of IL-1beta on firing rates in thermosensitive neurons of POAH were reversed by electrical stimulation of VSA. An arginine vasopressin (AVP) V1 antagonist abolished the regulatory effects of VSA on the firing rates in thermosensitive neurons of POAH evoked by IL-1beta. However, an AVP V2 antagonist had no effects. These data indicated that VSA regulates the activities of the thermosensitive neurons of POAH through AVP V1 but not AVP V2 receptor.

Suppression of proinflammatory cytokines interleukin-1beta and tumor necrosis factor-alpha in astrocytes by a V1 vasopressin receptor agonist: a cAMP response element-binding protein-dependent mechanism

Previous research from our laboratory has demonstrated that V1 vasopressin receptor agonist (V1 agonist) induces a complex intracellular Ca2+-signaling cascade in cortical astrocytes that is initiated by G-protein-coupled V1a vasopressin receptor-mediated cytoplasmic and nuclear Ca2+ rise and converges during activation of the nuclear transcription factor cAMP response element-binding protein (CREB). In the current study, we pursued the downstream functional consequences of V1 agonist-induced Ca2+-signaling cascade for gene expression. Because astrocytes can exert immune effects analogous to immune cells in the periphery, we investigated V1 agonist regulation of cytokine gene expression in astrocytes. Results from gene array studies indicated that V1 agonist dramatically decreased the mRNA level of five cytokines. Two prominent proinflammatory cytokines, interleukin-1beta (IL-1beta) and tumor necrosis factor-alpha (TNF-alpha), were selected for detailed analysis, and their expression was also confirmed with reverse transcriptase-PCR. Furthermore, ELISA analyses demonstrated that the peptide level of IL-1beta and TNF-alpha in the astrocyte medium was also decreased in response to V1 agonist. Using CREB antisense to determine the causal relationship between V1 agonist-induced CREB activation and suppression of IL-1beta and TNF-alpha, we demonstrated that decreased IL-1beta and TNF-alpha gene expression was dependent on upstream CREB activation. V1 agonist-induced decrease of cytokine release from cortical astrocytes was also shown to be neuroprotective in cortical neurons. To our knowledge, this is the first documentation of V1 agonist modulation of cytokine gene expression in any cell type. Implications for vasopressin as an antipyretic agent and the role of vasopressin in neurodegeneration, autoimmune diseases, stress, and neuropsychiatric behaviors are discussed.

Role of nitric oxide in thermoregulation during septic shock: involvement of vasopressin

We tested the hypothesis that the nitric oxide (NO) pathway in the central nervous system (CNS) plays a role in hypothermia, as well as in the febrile response during experimental septic shock, by regulating vasopressin (AVP) release. Experiments were performed on male Wistar rats treated with NG-nitro-L-arginine methyl ester (L-NAME), a non-selective NO synthase (NOS) inhibitor, injected intracerebroventricularly (250 microg/1 microl) 30 min before lipopolysaccharide (LPS) 1.5 mg/kg i.v. injection. One hour after LPS administration we observed a significant drop in body temperature (hypothermic response), followed by a temperature increase after the second hour (febrile response), which remained until the end of the experiment. Increased plasmatic AVP levels were concomitantly observed during hypothermia, nearly returning to basal levels during the febrile phase. When L-NAME was administered with LPS, plasmatic AVP concentrations remained high throughout the experiment, hypothermia was accentuated and the febrile response was abolished. Additionally, pre-treatment with beta-mercapto-beta,beta-cyclopentamethylenepropionyl1, O-Et-Tyr2, Val4, Arg8-vasopressin, an AVP V1 receptor blocker (10 microg/kg) administered i.v., reduced hypothermia and exacerbated the febrile response to endotoxin. In conclusion, our data indicate that the central NO pathway plays an inhibitory role in AVP release during experimental septic shock, which seems to be critical for the thermoregulation during this pathophysiological state.

Suppression of PGE(2) fever at near term: reduced thermogenesis but not enhanced vasopressin antipyresis

Fevers are known to be suppressed near term in the mother, but the mechanism responsible for this phenomenon is not understood. We tested the hypothesis that the suppression of fever at term is a result of enhanced vasopressin-induced antipyresis. Effects of intracerebroventricular prostaglandin E(2) (PGE(2)) were examined in rats at gestational days 16-17 and 19-20 (near term) and days 1-2 postpartum. PGE(2) (50 ng) elevated body and interscapular brown adipose tissue (iBAT) temperatures and increased sympathetic nerve activity to the iBAT. PGE(2)-induced changes in iBAT temperature and nerve activity, as well as in rectal temperature, were reduced or eliminated near term, and responses were recovered in the postpartum period. Blood pressure and heart rate changes induced by central PGE(2) were also decreased at near term. Coinfusion of Manning compound, a V(1) vasopressin receptor antagonist, with PGE(2) throughout the peripartum period did not reverse the suppressed iBAT temperature and nerve activity or body temperature responses to PGE(2). Microdialysis experiments revealed unchanged terminal release of vasopressin in the ventral septal area after PGE(2) infusion in either pregnant or parturient rats. These results suggest that fever reduction at near term is not associated with enhanced vasopressin antipyresis, but may be a result of reduced sympathetic tone and in particular a reduced sympathetic drive to the iBAT. This finding may reflect a generalized reduction in autonomic output around the time of parturition.

Effects of vasopressin and related peptides on neurons of the rat lateral septum and ventral hippocampus

The effects of vasopressin (VP), VP fragments and propressophysin glycopeptide on neuronal activities in the septum-hippocampus complex of rats were studied in vitro and in vivo. The frequency of the hippocampus theta rhythm in Brattleboro rats homozygous for diabetes insipidus was significantly slower than that of heterozygous litter mates and normal rats. Intracerebroventricular micro-injection of des-glycine-amide vasopressin corrected for several hours the frequency deficit of the theta rhythm in the homozygous Brattleboro rats and the centrally administered VP slowed down theta rhythm in normal rats. Microinotophoretically administered VP excited single neurons in the lateral septum of ventral hippocampus, and/or facilitated the responses of these neurons to glutamate and to stimulation of the glutamatergic afferent fibers in the fimbria bundle. The excitatory effects of VP vanished within seconds after termination of the peptide administration, however, the peptide-induced enhancement of glutamate and syntatically induced excitations were sustained for up to 60 min after the peptide administration. In vitro, pM concentrations of VP, VP 4-8 and C-terminus glycopeptide of propresophysin facilitated for 30-60 min the glutamate-mediated EPSPs in neurons of the lateral septum or the ventral hippocampus. The EPSPs increase in the lateral septum neurons was not prevented by pretreatment with antagonist of the V1a type of the vasopressin receptor. The resting membrane potential and input resistance were not affected by the peptides. A low-frequency electrical stimulation in the diagonal Band of Broca or in the Bed nucleus of the stria terminals, sources of the vasopressinergic innervation of the septum, facilitated the negative wave of the filed potentials responses evoked in the lateral septum by stimulating the fimbria bundle fibers in control Long-Evans and Brattleboro rats heterozygous for diabetes insipidus. The field potential increase was sustained for several hours after the stimulation, and it was not occluded by long-term potentiation elicited by high frequency stimulation of the fimbria bundle afferent fibers. Brattleboro rats homozygous for diabetes insipidus failed to show the filed potential increase after the diagonal band stimulation. It is suggested that the long-lasting facilitation of glutamate-mediated excitations might be a physiological action of the propressophysin-derived peptides in the septum-hippocampus complex which, in concert with other forms of synaptic plasticity like the long-term potentiation, facilitates the hippocampus-mediated forms of learning and memory. This action is presumably related to the memory enhancing effect of the propressophysin-derived peptides.

Anatomy and function of extrahypothalamic vasopressin systems in the brain

The most prominent sites of vasopressin (VP) production in the rat brain are the paraventricular nucleus, the supraoptic nucleus, the suprachiasmatic nucleus, the bed nucleus of the stria terminalis (BST), and the medial amygdaloid nucleus (MA). Recently a number of new sites have been suggested, including the hippocampus, the diagonal band of Broca, and the choroid plexus. This chapter shows how differential regulation of these VP systems can be exploited to identify the contributions of individual VP systems to the various central functions in which VP has been implicated. It will focus on the development, anatomy, and function of the sexually dimorphic VP projections of the BST and MA. This system contains more cells and has denser projections in males than in females. This system is also extremely responsive to gonadal steroids as it only produces VP in the presence of gonadal steroids. It has been implicated in sexually dimorphic functions such as aggressive behavior as well as in non-sexually dimorphic functions such as social recognition memory. Using comparative studies done in prairie voles as an example, this chapter makes the case that the VP projections of the BST and MA may simultaneously generate sex differences in some brain functions and behaviors and prevent them in others.

Arginine vasopressin, fever and temperature regulation

While central administration of arginine vasopressin (VP) to the non-febrile rat at high doses can cause hypothermia, there is little evidence for a role for endogenous VP in normal thermoregulation. In contrast, VP arising from cell bodies in the bed nucleus of the stria terminalis and innervating the ventral septal areas and possibly the amygdala appears to be an endogenous antipyretic, i.e. a substance capable of reducing fever. As the synthesis of VP in bed nucleus neurons is dependent upon circulating androgens, female rats have much less VP in these cells and their projections than do male rats. In keeping with this, females may make use of VP to a lesser extent than do males to bring about antipyresis. The phenomenon whereby the VP receptor can become sensitized by previous exposure to VP may be responsible for some states of endogenous antipyresis, in which fevers are suppressed through overactivity of the vasopressinergic system. States of endogenous antipyresis can be revealed around the time of parturition in both the neonate and the mother.

Arginine vasopressin does not mediate the attenuated febrile response to intravenous IL-1beta in pregnant rats

Rats have an attenuated febrile response to intravenous endogenous pyrogen [e.g., interleukin-1beta (IL-1beta)] near the term of pregnancy. The present experiments were carried out on 25 nonpregnant and 32 pregnant rats to test the hypothesis that arginine vasopressin functioning as an endogenous antipyretic substance in the central nervous system mediates this attenuated febrile response. An intravenous injection of recombinant rat IL-1beta (rrIL-1beta) after intracerebroventricular vehicle produced a significant increase in core temperature in both nonpregnant and pregnant animals, the magnitude and duration of which was greater in the nonpregnant rats. In nonpregnant rats, intravenous rrIL-1beta after intracerebroventricular vasopressin V1-receptor antagonist accentuated the core temperature response compared with that observed with intravenous rrIL-1beta after intracerebroventricular vehicle. In pregnant animals, however, intravenous rrIL-1beta after intracerebroventricular vasopressin V1-receptor antagonist produced a decrease in core temperature rather than an increase in core temperature, which was observed with intravenous rrIL-1beta after intracerebroventricular vehicle. Thus our data do not support the hypothesis that a pregnancy-related activation of arginine vasopressin as an endogenous antipyretic substance in the central nervous system attenuates the febrile response to intravenous rrIL-1beta near the term of pregnancy in rats.

Vasopressin-induced antipyresis. Sex- and experience-dependent febrile responses

There is now good evidence that vasopressin (AVP) acts, in the male rat, as a neurotransmitter in the ventral septal area to reduce fever. In light of the well known sexual dimorphism in the AVP innervation of the brain, we asked if female rats would (a) display fevers different from those seen in male rats, (b) respond to AVP with antipyresis, (c) display evidence of endogenous AVP-induced antipyresis during fever, and (d) display altered fevers and AVP involvement as a function of hormonal status. Our experiments indicate that female rats display larger fevers to intracranial prostaglandin E2 (PGE2) but not to systemic lipopolysaccharide or interleukin-1 beta than do male rats. The larger fevers may be due, in part, to a lack of AVP-induced antipyresis, as an AVP antagonist elevates PGE2 fever in male but not in female rats and dialysates of the ventral septal area show increased AVP levels only in male rats during defervescence. Nonetheless, females respond to exogenous AVP with antipyresis. Throughout late pregnancy, parturition, and lactation, PGE2 fevers are reduced, but this appears to be due to a general suppression of autonomic output not involving enhanced AVP antipyresis. Fevers due to lipopolysaccharide and interleukin-1 beta are also suppressed at this time, and in some animals, fevers are dramatically suppressed at about the time of parturition. Our results indicate that female rats may utilize different strategies for antipyresis than do male rats and that hormonal status may influence both peripherally generated and centrally activated fevers.

CNS cell groups projecting to sympathetic outflow of tail artery: neural circuits involved in heat loss in the rat

In the rat, approximately 20% of total body heat-loss occurs by sympathetically mediated increases in blood flow through an elaborate system of arteriovenous anastomoses in the skin of its tail. In this study, the CNS cell groups that regulate this sympathetic outflow were identified by the viral transneuronal labeling method. Pseudorabies virus was injected into the wall of the ventral tail artery in rats that had their cauda equina transected to eliminate the somatic innervation of the tail. After 4-7 days survival, the pattern of CNS transneuronal labeling was studied. Sympathetic preganglionic neurons in the T11-L2 (mainly L1) levels of the intermediolateral cell column (IML) were labeled by 4 days. After 5 days, sympathetic pre-motor neurons (i.e., supraspinal neurons that project to the IML) were identified near the ventral medullary surface; some of these contained serotonin immunoreactivity. Additional groups of the sympathetic premotor areas were labeled by 6 days post-injection, including the rostral ventrolateral medulla (C1 adrenergic neurons), rostral ventromedial medulla, caudal raphe nuclei (serotonin neurons in the raphe pallidus and magnus nuclei), A5 noradrenergic cell group, lateral hypothalamic area and paraventricular hypothalamic area (oxytocin-immunoreactive neurons). Seven days after the PRV injections, additional cell groups in the telencephalon (viz., bed nucleus of the stria terminalis, medial and lateral preoptic areas and medial preoptic nucleus), diencephalon (viz., subincertal nucleus, zona incerta as well as dorsal, dorsomedial, parafascicular, posterior and ventromedial hypothalamic nuclei) and midbrain (viz., periaqueductal gray matter, precommissural nucleus, Edinger-Westphal nucleus and ventral tegmental area) were labeled. The discussion is focused on the CNS cell groups involved in the control of body temperature and fever.

C3H/HeJ mice are refractory to lipopolysaccharide in the brain

C3H/HeJ mice are refractory to lipolysaccharide (LPS) in the periphery, primarily because their macrophages do not respond to LPS and produce pro-inflammatory cytokines such as interleukin-1 (IL-1). To determine if they are also refractory to LPS in the brain, behavior of C3H/HeJ mice was compared to LPS-sensitive C3H/HeOuJ mice following intracerebroventricular (I.C.V.) injection of LPS. Whereas ICV injection of LPS (3-1000 ng/mouse) depressed social behavior, food motivation, object investigation and body weight in C3H/HeOuJ mice, C3H/HeJ mice were entirely refractory to LPS in the brain. To determine if the refractoriness of C3H/HeJ mice could result from an inability to synthesize IL-1, recombinant murine IL-1 was injected I.C.V. in both mouse strains. Central administration of IL-1 (1 or 2 ng/mouse) depressed social behavior and body weight similarly in both endotoxin-sensitive C3H/HeOuJ mice and endotoxin-resistant C3H/HeJ mice. That C3H/HeJ mice were refractory to the behavioral effects of central LPS, but not IL-1, suggests that microglia (and other cells in the brain) in C3H/HeJ mice have in common with peripheral macrophages, an inability to respond to LPS and produce cytokines. These data suggest a genetic basis for sickness behavior and demonstrate the utility of preventing central cytokine production in manipulating LPS-induced sickness behavior.

Neoplastic fever

Neoplastic fever, that is fever arising solely as a manifestation of malignancy, is not as common as was thought but still constitutes a troublesome symptom and is difficult to manage. The mechanism of neoplastic fever production involves cytokines such as tumour necrosis factor (TNF), interleukins 1 and 6 (IL-1, IL-6) and interferon (IFN), produced either by host macrophages in response to tumour, or sometimes by the tumour itself. The cytokines stimulate production of prostaglandins which act on the hypothalamus causing a change in the thermostatic set point. This mechanism is similar to that of infective fever. Paracetamol (acetaminophen) will often only partially lyse neoplastic fever but nonsteroidal anti-inflammatory drugs have been shown to be effective. On the basis of small studies, naproxen has been proposed as a useful test to discriminate between neoplastic and infective fever. If this is so, it must be acting through a pathway hitherto undescribed and specific to neoplastic fever. Other work shows that this group of drugs effectively lyses both types of fever. Therefore larger studies are needed to confirm or refute the "Naproxen test' and neoplastic fever remains a diagnosis of exclusion. In the future, cytokine antagonists may have a role in managing neoplastic fever, but, until their actions are better understood, nonsteroidal anti-inflammatory drugs remain the medication of choice if standard antipyretics have failed.

Prostaglandin fever in rats throughout the estrous cycle late pregnancy and post parturition

We have examined the influence of natural variations in endocrine status on the ability to generate a prostaglandin-induced fever in virgin female, pregnant and lactating rats and compared responses to those in male rats. Endocrine status of virgin female rats was assessed from examination of vaginal smears and time of parturition noted to enable accurate dating of pre- and postparturient fevers. Unanesthetized rats, previously prepared with intraventricular guide cannulas and intraperitoneal telemetry thermistors, were given intraventricular injections of prostaglandin E1 (2-100 ng/5 microliters) and temperatures monitored for 3 h after injection. Virgin females developed significantly larger fevers than did males at higher doses. There were no significant alterations in either fever height or duration as a function of the phase of the reproductive cycle in the females. Both pregnant and postparturient rats within the several days around birth displayed significantly lower fevers than did virgin females, but there was no further reduction in the immediate periparturient period. These data indicate that there are sex-, and possibly hormone-dependent differences in the central mechanisms involved in fever generation and antipyresis.

Central interleukin-1 beta stimulation of vasopressin release into the rat brain: activation of an antipyretic pathway

1. Arg8-vasopressin (AVP)-containing neurones of the bed nucleus of the stria terminalis (BST), which terminate in the ventral septal area (VSA) of the rat brain, provide a pathway which controls body temperature during fever. The present study was conducted to test the hypothesis that interleukin-1 beta (IL-1 beta) may trigger the antipyretic response by evoking AVP release from BST neurones projecting into the VSA. 2. The push-pull perfusion technique and radioimmunoassay were utilized to determine the AVP concentrations of retrieved VSA perfusion fluid in urethane-anaesthetized rats following BST infusion of vehicle or IL-1 beta (125 or 500 pg (2 microliters)-1). 3. Ventral septal AVP levels significantly increased from basal levels, in a dose-related manner, in response to IL-1 beta (0-500 pg). Electrical stimulation of the same areas of the BST also evoked AVP release into the VSA. 4. IL-1 beta infusions and electrical stimulation of the BST resulted in significant increases in rectal temperature. In IL-1 beta-treated animals (500 pg), the change in body temperature and VSA AVP release were negatively correlated (P < 0.001). However, external heating of the animals to approximately the same levels as electrically stimulated or IL-1 beta treated rats did not affect basal AVP release. 5. These data show that IL-1 beta is a potent stimulus for AVP release from BST neurones and supports BST involvement in neuro-immune interactions. We propose, that in addition to febrogenesis, IL-1 beta is also a key component in the process of endogenous antipyresis by activating vasopressinergic BST neurones to release AVP during fever.

Lack of fever suppression or central AVP release in 1K1C hypertensive rats

Previous studies from our laboratory showed a transient suppression of the febrile response to intracerebroventricular (i.c.v.) PGE1 in the one-kidney, one-clip (1K1C) model of hypertension. This may have been due to an enhanced vasopressinergic transmission since arginine vasopressin (AVP), acting within the central nervous system (CNS), is thought to mediate endogenous antipyresis. These initial experiments utilized a protocol for the induction of 1K1C hypertension which produced an initial rapid rise in blood pressure, evident by day 4 following surgery, with a corresponding inhibition of the febrile response. The present experiments utilized a more slowly developing 1K1C hypertension (evident by day 12 following surgery) to firstly attempt to determine if inhibition of the febrile response is due to the actual change in blood pressure or to neural signals arising from the clipped kidney, and secondly to determine if the concentration of AVP in push-pull perfusates of the ventral septal area (VSA) of pyrogen-treated sham-operated and 1K1C rats were altered. In urethane-anaesthetized rats, i.c.v. PGE2 evoked brisk monophasic fevers in both 1K1C and sham-operated animals, with no significant difference between fever heights. Consistent with this, we found no increase in immunoreactive AVP from perfusates of the VSA of 1K1C rats. These results suggest that there is no inhibition of the febrile response to PGE2 when a slower developing hypertension is induced, nor is there an elevated release of AVP into the VSA under our conditions. We conclude that a rapid increase in blood pressure, and not high blood pressure per se, is required to produce an inhibition of the febrile response.

Alteration of the physiological responses to indomethacin by endotoxin tolerance in the rat: a possible role for central vasopressin

1. Previous studies suggest that arginine vasopressin (AVP) is released into the ventral septal area (VSA) of the rat brain during the antipyresis induced by the cyclo-oxygenase inhibitor indomethacin. In addition, there is evidence for increased AVP transmission in the VSA of animals having a reduced pyretic response following three intravenous injections of bacterial endotoxin (LPS) (endotoxin tolerant). Since ventral septal AVP receptors can also become 'sensitized' following exposure to AVP, we questioned whether the antipyretic action of indomethacin would increase, via an action involving central AVP, if this drug were administered into LPS-tolerant rats. 2. Intraperitoneal indomethacin (7.5 mg kg-1) was effectively antipyretic when administered 2 h after an intravenous challenge with LPS (50 micrograms kg-1) into conscious unrestrained rats. This dose of indomethacin had no effect on the core temperature of non-febrile rats given intravenous 0.9% pyrogen-free saline. 3. Three intravenous injections of LPS over a period of 3 days resulted in rats that were tolerant to the pyrogenic effects of LPS. When indomethacin was administered 2 h following the third LPS injection, a dose-dependent hypothermia was observed. This effect was age dependent, as profound hypothermia was seen in 8 week but not 20 week old rats. 4. A mortality rate of 41% (P = 0.02) was observed within 24 h of indomethacin treatment in 8 week old tolerant rats compared with 0% in 8 week old non-tolerant and 20 week old tolerant rats.(ABSTRACT TRUNCATED AT 250 WORDS)

Fever: causes and consequences

The present review distinguishes pathogenic, neurogenic, and psychogenic fever, but focuses largely on pathogenic fever, the hallmark of infectious disease. The data presented show that a complex cascade of events underlies pathogenic fever, which in broad outline - and with frank disregard of contradictory data - can be described as follows. An invading microorganism releases endotoxin that stimulates macrophages to synthesize a variety of pyrogenic compounds called cytokines. Carried in blood, these cytokines reach the perivascular spaces of the organum vasculosum laminae terminalis (OVLT) and other regions near the brain where they promote the synthesis and release of prostaglandin (PGE2). This prostaglandin then penetrates the blood-brain barrier to evoke the autonomic and behavioral responses characteristic of fever. But then once expressed, fever does not continue unchecked; endogenous antipyretics likely act on the septum to limit the rise in body temperature. The present review also examines fever-resistance in neonates, the blunting of fever in the aged, and the behaviorally induced rise in body temperature following infection in ectotherms. And finally it takes up the question of whether fever enhances immune responsiveness, and through such enhancement contributes to host survival.

Central effects of interleukin-1 on blood pressure, thermogenesis, and the release of vasopressin, ACTH, and atrial natriuretic peptide

To assess the central role of interleukin 1-beta (IL-1 beta) in the release of ACTH, vasopressin (AVP) and atrial natriuretic peptide (ANP) and in the regulation of blood pressure and thermogenesis, 3 ng (0.173 pM) x 100-1 x BW-1 (LIL), 30 ng (1.73 pM) x 100g-1 x BW-1 (MIL), and 150 ng (8.63 pM) x 100g-1 x BW-1 (HIL) of human IL-1 beta dissolved in sterile saline were injected intracerebroventricularly to conscious rats. In the control rats, saline alone (5 microliters) was administered. In three other groups, rats were pretreated with indomethacin, a cyclooxygenase inhibitor, given i.v. (1 mg x 100g-1 x BW-1); medium and high doses of IL-1 beta or its vehicle were given. In the LIL group, IL-1 beta increased blood pressure, body temperature and plasma AVP and ANP without any changes in heart rate (HR) and plasma ACTH. In the MIL group, plasma ACTH was increased, and changes in the other parameters were similar to those in the LIL group. In the HIL group, however, the pressor and thermogenetic responses were attenuated; plasma AVP, ACTH, and ANP were increased; and HR was unchanged. In the control (CON) group, none of these parameters was changed throughout the studies. Indomethacin abolished the AVP and ACTH responses to IL-1 beta, but potentiated the pressor and hypothermic responses and increased plasma ANP. These data suggest that the actions of IL-1 beta on AVP and ACTH release and thermogenesis, but not on blood pressure and the release of ANP, are modulated by the stimulated central production of prostaglandins.

Chronic intracerebral infusions of vasopressin and vasopressin antagonist modulate behavioral effects of interleukin-1 in rat

To assess the role of sex dependent brain vasopressinergic transmission in the modulation of the neural effects of interleukin-1, castrated male rats that are deficient in vasopressin were implanted intracerebroventricularly with an Accurel collodion mini device containing 10 micrograms AVP whereas intact male rats were implanted with a similar device containing 50 micrograms of dPTyr(Me)AVP, a specific antagonist of the vasopressor-like receptors of vasopressin. Control rats in each sex group were implanted with an Accurel device containing distilled water. Acute intracerebroventricular injection of 1.25-2.50 ng recombinant human interleukin-1 beta decreased in a dose and time-dependent manner social investigation of a juvenile conspecific. This effect was more intense in intact rats chronically infused with dPTyr(Me)AVP and less intense in castrates infused with AVP. These results confirm the modulatory role of sex-dependent vasopressinergic neurotransmission on the neural effects of interleukin-1.

Electrical stimulation of the paraventricular nucleus attenuates pyrogen fever in the rabbit

Arginine vasopressin (AVP) perfused within the ventral septal area (VSA) suppresses fever normally evoked by pyrogenic substances, including Salmonella abortus equi (SAE). Neurons containing AVP and located within the paraventricular nucleus (PVN) or the nearby bed nucleus of the stria terminalis (BnST) are believed to have projections to this septal region. A series of experiments was undertaken to determine whether electrical stimulation of these areas, which might be expected to cause the release of AVP within the VSA, would affect similarly the pathogenesis of fever. A stainless steel cannula was implanted surgically in each of 22 male New Zealand White rabbits and a monopolar electrode was lowered through this guide cannula to the PVN or BnST areas. Electrical stimulation (20 Hz, 10 s on, 10 s off, 2.6-3.2 V) was initiated 30 min prior to and was continued until 90 min after the intravenous (i.v.) administration of 0.1-1.0 micrograms of SAE (1.0 ml carrier vehicle). While afebrile body temperature remained unchanged, electrical stimulation of sites located in the rostral extension of the PVN effectively attenuated the pyrogen-induced fever. Stimulation of sites outside these areas did not affect either the absolute magnitude or the duration of the fever. Although the reduction in fever was most pronounced during the period of electrical stimulation, in some cases the fever remained suppressed beyond the application of the current. These experiments provide the first evidence that electrical stimulation of paraventricular areas with AVP-containing cell bodies is effective in suppressing a fever evoked by systemic administration of a pyrogen. Although untested, it is possible that a stimulus-induced release of AVP within the VSA is responsible for the attenuation of the fever.

Antipyretic effect of central arginine8-vasopressin treatment: V1 receptors specifically involved?

Intracerebroventricular (i.c.v.) administration of the neurohypophyseal neuropeptide arginine8-vasopressin (AVP) results in a dose-dependent attenuation of endotoxin-induced fever (EIF) in rats. Specific antagonists of the neuropeptided(CH2)5[Tyr(Me)2]AVP for V1 receptors, d(CH2)5[dlle2lle4]AVP for the V2 receptors and Des-Gly,NH2d(CH2)5[Tyr)Me2)Thr4Orn8]vasotocin, an antagonist of the oxytocin receptors (AOXT), failed to modify EIF when administered i.c.v. Relatively high doses (100 ng) of all three peptide antagonists effectively blocked the antipyretic effect of AVP. Administered in smaller doses (10 or 30 ng), however, a more specific interaction was observed, i.e. the V1 antagonist being the only effective compound in preventing the effect of AVP. Although the data indicate that peptide-antagonist interactions should be interpreted carefully, the present experiments confirm previous observations on the involvement of V1-type receptors in the antipyretic action of AVP and suggest additional interactions with V2 vasopressinergic and oxytocinergic receptors.

Androgen-dependent vasopressinergic neurotransmission attenuates interleukin-1-induced sickness behavior

Castrated male rats were found to be more sensitive than intact male rats to the depressing effects of recombinant human interleukin-1 beta (Il-1) on social exploration. This was the case whether Il-1 was injected acutely (1-5 micrograms/rat, i.p.) or continuously, via an implanted osmotic mini-pump (2 micrograms Il-1 per day). In this latter case, tolerance developed more rapidly to the behavioral effects of Il-1 than to its effects on body weight. Since there is evidence that extrahypothalamic arginine vasopressin (AVP) acts as an endogenous antipyretic in the brain and the local concentration of AVP is dependent on circulating androgens, we tested the hypothesis that the enhanced sensitivity of male rats to the behavioral effects of Il-1 was caused by a reduced brain concentration of vasopressin. Central injection of AVP (2.5 ng, i.c.v.) attenuated the behavioral effects of Il-1 (5 ng, i.c.v.) and this effect was more marked in castrated than in intact male rats. Conversely, central injection of an antagonist of the vasopressor receptors of AVP, dPTyr(Me)AVP (15 ng, i.c.v.) potentiated the behavioral effects of Il-1 (1 ng, i.c.v.) in intact but not in castrated male rats. These results are consistent with the possibility that androgen-dependent vasopressinergic neurons oppose the neural effects of Il-1.

The effectiveness of arginine vasopressin and sodium salicylate as antipyretics in the Brattleboro rat

The infusion of either 30 micrograms/microliters (approx. 100 micrograms/kg/h) of sodium salicylate or 10 ng/microliters (10(-5) M) arginine vasopressin within the ventral septal area of the Brattleboro rat brain reduced a centrally induced prostaglandin E1 (PGE1) hyperthermia when compared with infusions of artificial cerebrospinal fluid. Conversely, the infusion of a related peptide, oxytocin (10 ng/microliters (10(-5) M), or 33 ng/kg/h) failed to alter the rise in core temperature following the PGE1 injection. These results suggest that the vasopressin receptors reported to be present in the Brattleboro rat may respond normally to exogenously administered vasopressin, thus allowing for the antipyretic action. Moreover, the antipyretic effects of sodium salicylate suggest that aspirin-like drugs may induce the release of alpha-melanocyte-stimulating hormone which, in turn, attenuates the PGE1-evoked fever. Given recent evidence, however, which suggests that the Brattleboro rat may contain vasopressin both peripherally and within the brain, the antipyretic action of sodium salicylate may be alternatively explained through the endogenous release of vasopressin.

Indomethacin-induced antipyresis in the rat: role of vasopressin receptors

Infusion of 15 micrograms/microliters (approximately 120 micrograms/kg/h) of indomethacin within the ventral septal area of the rat brain significantly reduced a centrally induced prostaglandin E1 (PGE1) hyperthermia when compared with infusions of artificial cerebrospinal fluid. A bolus injection of a V1 receptor antagonist, d(CH2)5Try(Me)AVP, (200, 2000, or 20,000 pmol) within the ventral septal area had no effect of body temperature alone but did suppress the PGE1-induced fever. Similar bolus injections of the V1 receptor antagonist within the ventral septal area failed to alter the antipyretic action of indomethacin on the hyperthermia resulting from centrally administered PGE1. Central injections of a V2 receptor antagonist failed to alter either the PGE1-induced fever or the indomethacin-evoked antipyresis. The results suggest that the V1 receptor antagonist may exert non-specific neurodepressant effects which may interfere with the expression or production of PGE1 hyperthermia and may further mask any contribution of arginine vasopressin to the antipyretic effects of indomethacin.

Single-unit activity in the bed nucleus of the stria terminalis during fever

Arginine vasopressin, released from nerve terminals in the septal region, probably exerts endogenous antipyretic activity. A major source of vasopressin to this area is the bed nucleus of the stria terminalis (BST). In order to characterize electrophysiologically the BST-septal pathway and its potential role in the control of fever, single-unit, extracellular recordings were made from neurons in the BST of anesthetized rats. Afferent and efferent connections were identified by electrical stimulation of the medial amygdaloid nucleus and the ventral septal area (VSA). BST neurons received both inhibitory and excitatory synaptic input from the amygdala and VSA. Efferents to the VSA were identified by stimulus-evoked antidromic spike invasion. Some BST neurons were responsive to peripheral skin temperature (thermoresponsive). The activity of putative vasopressin neurons was studied during prostaglandin E1-induced fever. Although a majority of BST units was unaffected by fever, a proportion of the cells examined increased their firing rates in accordance with reported release of vasopressin in the VSA during fever.

Criteria for establishing a physiological role for brain peptides. A case in point: the role of vasopressin in thermoregulation during fever and antipyresis

This paper has attempted to present and discuss the criteria necessary for the evaluation of a specific physiological role for a peptide in the CNS. These criteria are based on many experimental approaches to the problem and conclusions must be supported by the weight of the evidence. These criteria were illustrated by examining the hypothesis that AVP is an antipyretic neurotransmitter involved in regulating febrile increases in Tb by release and action in the VSA of the brain. The weight of the evidence in this case implies that this hypothesis is essentially correct. The only serious conflicting evidence comes from the work with Brattleboro rats. It is hoped that further research will resolve these discrepancies or result in a suitably modified hypothesis.

Measurement of septal release of vasopressin and oxytocin by the push-pull technique following electrical stimulation of the paraventricular nucleus of rats

The release of vasopressin (AVP) and oxytocin (OXT) within the septum was studied with the push-pull perfusion technique in 6 conscious, freely behaving male rats. Push-pull perfusion was performed via a chronically implanted cannula and samples collected for 3 consecutive 30-min periods. Stimulating electrodes were implanted in both the left and right paraventricular nuclei 4 days before the experiment. Bilateral electrical stimulation (10-s trains every 4 min) of the paraventricular nuclei during the second 30-min period resulted in a significant increase in the release of both AVP and OXT (128% and 159% of control values respectively); release returned to the pre-stimulation value during the final 30-min collection.

The role of vasopressin as an antipyretic in the ventral septal area and its possible involvement in convulsive disorders

Perfusion of the peptide, arginine vasopressin (AVP), within the ventral septal area (VSA) of the brain of a number of species reduces fever but not normal body temperature. This antipyretic response appears to be mediated by AVP receptors of the V1 subtype. Lesions of the VSA with kainic acid are associated with prolonged and enhanced fevers in rats. A role for endogenous AVP in fever suppression within the VSA comes from several types of experiments: (1) AVP release within the VSA is inversely correlated to fever height; (2) AVP antagonists or antiserum injected into the VSA prolong fever; (3) animals lacking endogenous AVP in the VSA (Brattleboro rat, long-term castrated rat) develop enhanced fevers. Electrical stimulation of the AVP-containing cell bodies of the bed nucleus of the stria terminalis (BST) orthodromically inhibits VSA neurons and also suppresses fever; the latter effect can be abolished with application of a V1 antagonist to the VSA. Iontophoretic studies indicate that AVP inhibits glutamate-stimulated activity of thermoresponsive and other VSA neurons. AVP can also act in the VSA to cause severe motor disturbances; this action is receptor mediated and increases in severity upon sequential exposure to AVP. Because sites of action of the antipyretic and convulsive action of AVP are similar, and because animals lacking brain AVP display reduced convulsive activity, it is possible that AVP, released during fever, could be involved in the genesis of convulsive activity.