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

Reduction in vasopressin cells in the suprachiasmatic nucleus in mice increases anxiety and alters fluid intake

Central vasopressin (AVP) has been implicated in the control of multiple behaviors, including social behavior, anxiety-like behavior, and sickness behavior. The extent to which the different AVP-producing cell groups contribute to regulating these behaviors has not been extensively investigated. Here we test the role of AVP cells in the suprachiasmatic nucleus (SCN) in these behaviors by ablating these cells using viral-mediated, Cre-dependent caspase in male and female AVP-Cre + mice and Cre-controls. We compared anxiety and social behaviors, as well as sickness behaviors (lethargy, anhedonia (indexed by sucrose consumption), and changes in anxiety-like- and social behavior) induced via injection of bacterial lipopolysaccharide (LPS). We found that SCN AVP cell ablation increased anxiety-like behavior and sucrose consumption in both sexes, as well as increased urine marking by males in a non-social context, but did not alter behavioral responses to sickness. Our data suggest that SCN AVP does not strongly affect LPS-induced behavioral changes, but may contribute to anxiety-like behavior, and may play a role in ingestive reward/motivation and fluid intake.

Sickness behaviors across vertebrate taxa: proximate and ultimate mechanisms

There is nothing like a pandemic to get the world thinking about how infectious diseases affect individual behavior. In this respect, sick animals can behave in ways that are dramatically different from healthy animals: altered social interactions and changes to patterns of eating and drinking are all hallmarks of sickness. As a result, behavioral changes associated with inflammatory responses (i.e. sickness behaviors) have important implications for disease spread by affecting contacts with others and with common resources, including water and/or sleeping sites. In this Review, we summarize the behavioral modifications, including changes to thermoregulatory behaviors, known to occur in vertebrates during infection, with an emphasis on non-mammalian taxa, which have historically received less attention. We then outline and discuss our current understanding of the changes in physiology associated with the production of these behaviors and highlight areas where more research is needed, including an exploration of individual and sex differences in the acute phase response and a greater understanding of the ecophysiological implications of sickness behaviors for disease at the population level.

Love and fear in the times of sickness

Sickness induced by gastrointestinal malaise or by microbial pathogens is more than a private experience. Sick individuals share their illness within their social environment by communicating their sickness to others. In turn, recipients of the communication respond with appropriate behavioral adaptations. Avoidance of sick individuals and the events associated with their sickness is advantageous for members of the group. However, these responses can conflict with the need for comfort or social support expressed by sick individuals. There is evidence that the relationship between the sick individual and its social environment involves neurobiological mechanisms that are similar to those that mediate social bonding. Despite their commonality the feelings of love and fear/disgust that are associated with the sociality of sickness have thus far been neglected by mainstream affective neuroscience.

Removal of vasopressin cells from the paraventricular nucleus of the hypothalamus enhances lipopolysaccharide-induced sickness behaviour in mice

Vasopressin (AVP) cells in the paraventricular nucleus of the hypothalamus (PVN) are activated during sickness and project to multiple nuclei responsible for the anxiety, social and motivated behaviours affected during sickness, suggesting that these cells may play a role in sickness behaviours, typically expressed as reduced mobility, increased anxiety, anhedonia and social withdrawal. In the present study, we selectively ablated AVP neurones in the PVN of male and female mice (Mus musculus) and induced sickness behaviour via injection of bacterial lipopolysaccharide (LPS). We found that PVN AVP ablation increased the effects of LPS, specifically by further decreasing sucrose preference in males and females and decreasing the social preference of males, monitored within 24 hours of LPS injection. These results suggest that PVN AVP contributes to the change in motivated behaviours during sickness and may help promote recovery from infection..

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.

The humoral immune system of anadromous fish

The immune system of anadromous fish is extremely complex, a direct consequence of their diadromous nature. Hormone levels fluctuate widely throughout their life cycle, as fish move between fresh and salt water. This poses major challenges to the physiology of anadromous fish, including adaptation to very different saline environments, distinct pathogen fingerprints, and different environmental stressors. Elevated cortisol and sex hormone levels inhibit B lymphopoiesis and IgM⁺ antibody responses, while catecholamines, growth hormones and thyroid hormones are generally stimulatory and enhance the humoral immune response. Immunological memory in the form of long-lived plasma cells likely plays important roles in health and survival during the life cycle of anadromous fishes. This review discusses some of the complex immune-endocrine pathways in anadromous fish, focusing on essential roles for B lineage cells in the successful completion of their life cycle. A discussion is included on potential differences in immuno-competence between wild and hatchery-raised fish.

A new focal model resembling features of cortical pathology of the progressive forms of multiple sclerosis: Influence of innate immunity

Multiple sclerosis (MS) is an inflammatory and demyelinating disease of unknown aetiology that causes neurological disabilities in young adults. MS displays different clinical patterns, including recurrent episodes with remission periods ("relapsing-remitting MS" (RRMS)), which can progress over several years to a secondary progressive form (SPMS). However, 10% of patients display persistent progression at the onset of disease ("primary progressive MS" (PPMS)). Currently, no specific therapeutic agents are available for the progressive forms, mainly because the underlying pathogenic mechanisms are not clear and because no animal models have been specifically developed for these forms. The development of MS animal models is required to clarify the pathological mechanisms and to test novel therapeutic agents. In the present work, we overexpressed interleukin 1 beta (IL-1β) in the cortex to develop an animal model reflecting the main pathological hallmarks of MS. The treated animals presented with neuroinflammation, demyelination, glial activation, and neurodegeneration along with cognitive symptoms and MRI images consistent with MS pathology. We also demonstrated the presence of meningeal inflammation close to cortical lesions, with characteristics similar to those described in MS patients. Systemic pro-inflammatory stimulation caused a flare-up of the cortical lesions and behavioural symptoms, including impairment of working memory and the appearance of anxiety-like symptoms. Our work demonstrated induced cortical lesions, reflecting the main histopathological hallmarks and cognitive impairments characterizing the cortical pathology described in MS patients with progressive forms of the disease.

Mouse Testing Methods in Psychoneuroimmunology 2.0: Measuring Behavioral Responses

The field of psychoneuroimmunology (PNI) aims to uncover the processes and consequences of nervous, immune, and endocrine system relationships. Behavior is a consequence of such interactions and manifests from a complex interweave of factors including immune-to-neural and neural-to-immune communication. Often the signaling molecules involved during a particular episode of neuroimmune activation are not known but behavioral response provides evidence that bioactives such as neurotransmitters and cytokines are perturbed. Immunobehavioral phenotyping is a first-line approach when examining the neuroimmune system and its reaction to immune stimulation or suppression. Behavioral response is significantly more sensitive than direct measurement of a single specific bioactive and can quickly and efficiently rule in or out relevance of a particular immune challenge or therapeutic to neuroimmunity. Classically, immunobehavioral research was focused on sickness symptoms related to bacterial infection but neuroimmune activation is now a recognized complication of diseases and disorders ranging from cancer to diabesity to Alzheimer's. Immunobehaviors include lethargy, loss of appetite, and disinterest in social activity/surrounding environment. In addition, neuroimmune activation can diminish physical activity, precipitate feelings of depression and anxiety, and impair cognitive and executive function. Provided is a detailed overview of behavioral tests frequently used to examine neuroimmune activation in mice with a special emphasis on pre-experimental conditions that can confound or prevent successful immunobehavioral experimentation.

When is it socially acceptable to feel sick?

Disease is a ubiquitous and powerful evolutionary force. Hosts have evolved behavioural and physiological responses to disease that are associated with increased survival. Behavioural modifications, known as 'sickness behaviours', frequently involve symptoms such as lethargy, somnolence and anorexia. Current research has demonstrated that the social environment is a potent modulator of these behaviours: when conflicting social opportunities arise, animals can decrease or entirely forgo experiencing sickness symptoms. Here, I review how different social contexts, such as the presence of mates, caring for offspring, competing for territories or maintaining social status, affect the expression of sickness behaviours. Exploiting the circumstances that promote this behavioural plasticity will provide new insights into the evolutionary ecology of social behaviours. A deeper understanding of when and how this modulation takes place may lead to better tools to treat symptoms of infection and be relevant for the development of more efficient disease control programmes.

Mouse testing methods in psychoneuroimmunology: an overview of how to measure sickness, depressive/anxietal, cognitive, and physical activity behaviors

The field of psychoneuroimmunology (PNI) aims to uncover the processes and consequences of nervous, immune, and endocrine system relationships. Behavior is a consequence of such interactions and manifests from a complex interweave of factors including immune-to-neural and neural-to-immune communication. Often the signaling molecules involved during a particular episode of neuroimmune activation are not known but behavioral response provides evidence that bioactives such as neurotransmitters and cytokines are perturbed. Immunobehavioral phenotyping is a first-line approach when examining the neuroimmune system and its reaction to immune stimulation or suppression. Behavioral response is significantly more sensitive than direct measurement of a single specific bioactive and can quickly and efficiently rule in or out relevance of a particular immune challenge or therapeutic to neuroimmunity. Classically, immunobehavioral research was focused on sickness symptoms related to bacterial infection but neuroimmune activation is now a recognized complication of diseases and disorders ranging from cancer to diabesity. Immunobehaviors include lethargy, loss of appetite, and disinterest in social activity and the surrounding environment. In addition, neuroimmune activation can precipitate feelings of depression and anxiety while negatively impacting cognitive function and physical activity. Provided is a detailed overview of behavioral tests frequently used to examine neuroimmune activation in mice with a special emphasis on preexperimental conditions that can confound or prevent successful immunobehavioral experimentation.

The neuroimmune changes induced by cohabitation with an Ehrlich tumor-bearing cage mate rely on olfactory information

Cohabitation for 14 days with Ehrlich tumor-bearing mice was shown to increase locomotor activity, to decrease hypothalamic noradrenaline (NA) levels, to increase NA turnover and to decrease innate immune responses and decrease the animals' resistance to tumor growth. Cage mates of a B16F10 melanoma-bearer mice were also reported to show neuroimmune changes. Chemosignals released by Ehrlich tumor-bearing mice have been reported to be relevant for the neutrophil activity changes induced by cohabitation. The present experiment was designed to further analyze the effects of odor cues on neuroimmune changes induced by cohabitation with a sick cage mate. Specifically, the relevance of chemosignals released by an Ehrlich tumor-bearing mouse was assessed on the following: behavior (open-field and plus maze); hypothalamic NA levels and turnover; adrenaline (A) and NA plasmatic levels; and host resistance induced by tumor growth. To comply with such objectives, devices specifically constructed to analyze the influence of chemosignals released from tumor-bearing mice were employed. The results show that deprivation of odor cues released by Ehrlich tumor-bearing mice reversed the behavioral, neurochemical and immune changes induced by cohabitation. Mice use scents for intraspecies communication in many social contexts. Tumors produce volatile organic compounds released into the atmosphere through breath, sweat, and urine. Our results strongly suggest that volatile compounds released by Ehrlich tumor-injected mice are perceived by their conspecifics, inducing the neuroimmune changes reported for cohabitation with a sick companion.

Corticotropin releasing factor-1 receptor antagonism alters the biochemical, but not behavioral effects of repeated interleukin-1β administration

Activation of the immune system via administration of cytokines is used for the treatment of chronic viral infections such as hepatitis C and for cancers resistant to radiotherapy. Cytokine-based treatments induce a range of "sickness" behaviors (e.g. depression, anxiety, pain, anorexia, and fatigue). Activation of the hypothalamic pituitary-adrenal axis via the induction of corticotropin releasing factor (CRF) may underlie these unwanted side effects. This study used repeated systemic injections of the pro-inflammatory cytokine interleukin-1β (IL-1β) to model the sickness behaviors and biochemical effects of immune system activation. We assessed the ability of CRF type I receptor (CRF(1)) antagonism to reduce biochemical and behavioral signs of sickness induced by IL-1β treatment. Forty Wistar rats were assigned to one of four groups: 1) saline+vehicle; 2) saline+DMP904 (CRF(1) antagonist); 3) IL-1β+vehicle; 4) IL-1β+DMP904. Rats received intraperitoneal injections of either DMP904 or vehicle and of IL-1β or saline for six days. Sickness behavior was evaluated using body weight assessments and forced swim testing (FST). Blood and brain samples were collected to measure cytokine, p38 mitogen-activated protein kinase (MAPK), and phospho-p38 MAPK levels using multiplex techniques. There were significant reductions in body weights and FST immobility times associated with IL-1β administration. Rats administered IL-1β had significantly higher serum levels of IL-10, but not interferon-γ. Within the hippocampus, IL-1β reduced levels of p38 MAPK, but had no impact on levels of phospho-p38 MAPK except in the presence of DMP904. When administered alone, DMP904 had no significant effect on p38 MAPK or phospho-p38 MAPK in the hippocampus, but when given with IL-1β led to increased phosphorylation of p38 MAPK. IL-1β and DMP904 reduced levels of p38 MAPK within the hypothalamus, while co-administration of IL-1β and DMP904 abolished the effects of either drug alone. IL-1β decreased immobility time in the FST, and led to reductions in body weight, changes in serum cytokine levels and p38 MAPK regulation within the hippocampus and hypothalamus. DMP904 blocked some of the neurochemical effects of IL-1β, but did not impact the behavioral measures, or serum cytokines. Thus, additional studies will be needed to determine whether CRF(1) antagonism is an effective treatment for cytokine-induced sickness. This article is part of a Special Issue entitled 'Anxiety and Depression'.

Testing declarative memory in laboratory rats and mice using the nonconditioned social discrimination procedure

Testing declarative memory in laboratory rodents can provide insights into the fundamental mechanisms underlying this type of learning and memory processing, and these insights are likely to be applicable to humans. Here we provide a detailed description of the social discrimination procedure used to investigate recognition memory in rats and mice, as established during the last 20 years in our laboratory. The test is based on the use of olfactory signals for social communication in rodents; this involves a direct encounter between conspecifics, during which the investigatory behavior of the experimental subject serves as an index for learning and memory performance. The procedure is inexpensive, fast and very reliable, but it requires well-trained human observers. We include recent modifications to the procedure that allow memory extinction to be investigated by retroactive and proactive interference, and that enable the dissociated analysis of the central nervous processing of the volatile fraction of an individual's olfactory signature. Depending on the memory retention interval under study (short-term memory, intermediate-term memory, long-term memory or long-lasting memory), the protocol takes ~10 min or up to several days to complete.

Sickness-related odor communication signals as determinants of social behavior in rat: a role for inflammatory processes

Infected animals are avoided by conspecifics, suggesting that the inflammatory cascade may play a significant role in odor communication. Injection of male rats with the bacterial mimetic, lipopolysaccharide (LPS, 100 microg/kg, i.p.), decreased investigation through a wire-mesh partition between healthy male partners. This avoidance response was observed in adult males in response to soiled bedding collected from sick rats, regardless of whether LPS was injected peripherally (100 microg/kg, i.p.) or centrally (0.25 or 2.5 microg, icv). The release of sickness-related odor cues was dose-dependently blocked by icv infusion of the anti-inflammatory cytokine, interleukin-10 (IL-10; 20 or 200 ng), and reproduced by icv infusion of pro-inflammatory cytokine, IL-1beta (5 or 50 ng). Subcutaneous pretreatment with either estradiol benzoate (20 microg/kg) or testosterone propionate (50 or 500 microg/kg) to adult males that were administered LPS inhibited release of aversive odor cues, but these hormones alone did not influence odor properties. Importantly, the avoidance response to sickness-related odor was not associated with changes in plasma corticosterone, testosterone, or IL-6 levels of odor donors. However, plasma IL-1beta concentrations of sick animals was in fact predictive of aversive responses in conspecifics, suggesting that the inflammatory cascade, but not plasma steroid hormones, is likely to mediate aversive properties in odor that functions to signal illness state to conspecifics.

Neuroimmune mechanisms of cytokine-induced depression: current theories and novel treatment strategies

The relationships between immune and neural function are an increasingly important area of study for neuropsychiatric disorders, in particular depression. This is exemplified by the growing number of publications on cytokines and depression during the last 10 years, as compared to earlier decades. This review summarizes the current theories and novel treatment strategies for depression, with a focus on cytokine-induced depression. Neuroimmune mechanisms are now viewed as central to the development of depressive symptoms and emerging evidence is beginning to identify the neural circuits involved in cytokine-induced depression. The current diagnostic categories for depression, as defined by the Diagnostic and Statistical Manual of Mental Disorders, however, are not etiologically or biologically derived, and it has been proposed that "depression", likely reflects multiple pathogeneses leading to varying symptom constellations. As we move toward a better biological understanding of depression-related symptom constellations or syndromes, the term "depression" may prove inadequately broad, and an integration of interdisciplinary literatures will increase in importance. Future research should aim to characterize these depression-related symptom constellations or syndromes better with the goal of optimizing treatment strategies.

Central infusion of interleukin-1 receptor antagonist blocks the reduction in social behavior produced by prior stressor exposure

Pro-inflammatory cytokines such as interleukin-1beta (IL-1beta) in the brain modulate sickness behavior in rodents, in which animals show complex changes in behavior such as the reduction of general activity, reduced social motivation, and fever response. The present studies examined the impact of lipopolysacharide (LPS) and stressor (footshock) exposure on the later expression of social behavior in Sprague-Dawley rats using two separate behavioral paradigms. In Experiment 1, a traditional test for social interaction in which animals were allowed to investigate a juvenile rat in their home cages was conducted at 4 different time points following LPS or footshock treatment. In Experiment 2, social investigation task which allowed the animals to sniff the hole connected to the other chamber where a stimulus animal was placed, but prevented physical contact, was used to measure social investigation at several time points following LPS or footshock treatment. Both systemic infusion of LPS (100 microg/kg) and 2 h footshock exposure (80 shocks, 1 mA, 5 s duration) elicited a time-dependent reduction of social interaction (Experiment 1) and investigation (Experiment 2); LPS-treated rats displayed a more profound reduction of social investigation from 2 h to 6 h after treatment, while rats exposed to footshock showed a reduction 6 h after the footshock exposure. In Experiment 3, the footshock-induced reduction of social investigation was blocked by pretreatment with IL-1 receptor antagonist (IL-1Ra; 100 microg icv) infusion. Together, these findings support a growing body of literature showing that stress-dependent changes in brain cytokines play a key role in mediating behavioral consequences of stressor exposure.

Molecular and cellular immune mediators of neuroprotection

Our view of the immune privileged status of the brain has dramatically changed during the past two decades. Even though systemic immune stimuli have the ability to activate different populations of neurons, cells of monocytic lineage also have access to the neuronal tissue and populate it as microglia. Although such a phenomenon is limited in intact brains, it is greatly increased during neurodegenerative processes associated with innate immunity and the release of pro-inflammatory molecules by either resident microglia or those derived from the bone marrow stem cells. The role of these events is currently a matter of great debate and controversy, especially as it relates to brain protection, repair, or further injury. In recent years, accumulating data have supported the notion that when immune molecules are timely released by microglia, they limit neuronal injury in the presence of pathogens and toxic agents, help clear debris from degenerated cells, and restore the cerebral environment for repair. It has been shown that alteration of the natural innate immune response by microglia has direct consequences in exacerbating the damages following acute injury to neurons. This article presents and discusses these data, supporting a powerful neuroprotective role for microglia and their innate immune reactions in response to pathogens and central nervous system insults.

Cytokine-induced sickness behaviour: a neuroimmune response to activation of innate immunity

Sickness refers to a coordinated set of subjective, behavioural and physiological changes that develop in sick individuals during the course of an infection. These changes are due to the effects of interleukin-1 (IL-1) and other proinflammatory cytokines on brain cellular targets. Sickness behaviour is mediated by proinflammatory cytokines that are temporarily expressed in the brain during infection. These centrally produced cytokines are the same as those expressed by innate immune cells and they act on brain receptors that are identical to those characterized on immune cells. Primary afferent nerves represent the main communication pathway between peripheral and central cytokines. Proinflammatory cytokines modulate learning and memory processes. The expression and action of proinflammatory cytokines in the brain in response to peripheral cytokines are regulated by various molecular intermediates including anti-inflammatory cytokines such as interleukin-10 (IL-10) and the IL-1 receptor antagonist (IL-1ra), growth factors such as insulin-like growth factor-1 (IGF-1), hormones such as glucocorticoids and neuropeptides such as vasopressin and alpha-melanotropin.

Interleukin-1beta upregulates functional expression of neurokinin-1 receptor (NK-1R) via NF-kappaB in astrocytes

Cytokines and neuropeptides are modulators of neuroimmunoregulation in the central nervous system (CNS). The interaction of these modulators may have important implications in CNS diseases. We investigated whether interleukin-1beta (IL-1beta) modulates the expression of neurokinin-1 receptor (NK-1R), the primary receptor for substance P (SP), a potent neuropeptide in the CNS. IL-1beta upregulated NK-1R expression in human astroglioma cells (U87 MG) and primary rat astrocytes at both mRNA and protein levels. IL-1beta treatment of U87 MG cells and primary rat astrocytes led to an increase in cytosolic Ca(2+) in response to SP stimulation, indicating that IL-1beta-induced NK-1R is functional. CP-96,345, a specific non-peptide NK-1R antagonist, inhibited SP-induced rise of [Ca(2+)](i) in the astroglioma cells. Investigation of the mechanism responsible for IL-1beta action revealed that IL-1beta has the ability of activating nuclear factor-kappab (NF-kappaB). Caffeic acid phenethyl ester (CAPE), a specific inhibitor of NF-kappaB activation, not only abrogated IL-1beta-induced NF-kappaB promoter activation, but also blocked IL-1beta-mediated induction of NK-1R gene expression. These findings provide additional evidence that there is a biological interaction between IL-1beta and the neuropeptide SP in the CNS, which may have important implications in the inflammatory diseases in the CNS.

Peripheral vasopressin accelerates extinction of conditioned taste avoidance

Both peripheral and central administration of vasopressin improves retention and delays extinction when given before or after acquisition of shock avoidance learning. For conditioned taste avoidance, however, vasopressin prolongs extinction when injected peripherally before acquisition tests and accelerates extinction when infused intracerebroventricularly after acquisition. The following experiments were designed to determine whether this inconsistency is based on the route of administration or timing of vasopressin treatment. Because acquisition of conditioned taste avoidance is strengthened when an agent that is capable of inducing avoidance is administered after LiCl injection, it was determined in experiment 1 that a 6 microg/kg dose of vasopressin did not induce conditioned taste avoidance when administered 50 min after consumption of a sucrose solution. In experiment 2, it was determined that this dose of vasopressin accelerated extinction of a LiCl-induced conditioned taste avoidance when given 50 min after LiCl injection. These results suggest that the inconsistency is not based on route of administration. In experiment 3, it was determined that there was a tendency for animals to show prolonged extinction when vasopressin was administered 20 min before access to a sucrose solution. All of the results taken together suggest that the differential effects of vasopressin on extinction are due to the timing of administration. It was suggested that vasopressin accelerates extinction when given after acquisition by reducing the effectiveness of LiCl and it prolongs extinction when given before acquisition by altering neural responsiveness in areas mediating conditioned taste avoidance.

Interleukin-1beta stimulates macrophage inflammatory protein-1alpha and -1beta expression in human neuronal cells (NT2-N)

Chemokines are important mediators in immune responses and inflammatory processes of neuroimmunologic and infectious diseases. Although chemokines are expressed predominantly by cells of the immune system, neurons also express chemokines and chemokine receptors. We report herein that human neuronal cells (NT2-N) produce macrophage inflammatory protein-1alpha and -1beta (MIP-1alpha and MIP-1beta), which could be enhanced by interleukin (IL)-1beta at both mRNA and protein levels. The addition of supernatants from human peripheral blood monocyte-derived macrophage (MDM) cultures induced MIP-1beta mRNA expression in NT2-N cells. Anti-IL-1beta antibody removed most, but not all, of the MDM culture supernatant-induced MIP-1beta mRNA expression in NT2-N cells, suggesting that IL-1beta in the MDM culture supernatants is a major factor in the induction of MIP-1beta expression. Investigation of the mechanism(s) responsible for IL-1beta-induced MIP-1alpha and -1beta expression demonstrated that IL-1beta activated nuclear factor kappa B (NF-kappaB) promoter-directed luciferase activity in NT2-N cells. Caffeic acid phenethyl ester, a potent and specific inhibitor of activation of NF-kappaB, not only blocked IL-1beta-induced activation of the NF-kappaB promoter but also decreased IL-1beta-induced MIP-1alpha and -1beta expression in NT2-N cells. These data suggest that NF-kappaB is at least partially involved in the IL-1beta-mediated action on MIP-1alpha and -1beta in NT2-N cells. IL-1beta-mediated up-regulation of beta-chemokine expression may have important implications in the immunopathogenesis of inflammatory diseases in the CNS.

Central infusion of vasopressin in male rats accelerates extinction of conditioned taste avoidance induced by LiCl

In shock avoidance tasks, extinction is prolonged when vasopressin is infused into the lateral ventricle after an acquisition session. Experiments were performed to determine whether a dose of vasopressin that does not induce conditioned taste avoidance (CTA) could prolong extinction of a LiCl-induced CTA when it is infused into the lateral ventricle of Sprague-Dawley male rats after acquisition. The first experiment was designed to determine whether infusion of vasopressin into the lateral ventricle would induce a CTA. Consumption of a sucrose solution was paired with infusion of vasopressin or saline, and even after two pairings, none of the vasopressin-treated rats showed decreases in sucrose consumption. Therefore, in the second experiment, this same dose of vasopressin was infused into the lateral ventricle 50 min after consumption of a sucrose solution was paired with an injection of LiCl. Vasopressin increased the rate of extinction of the LiCl-induced CTA. These results are the opposite of what has been found after peripheral administration of vasopressin before acquisition and/or extinction of a LiCl-induced CTA. Possible reasons for the difference in the direction of the effect on extinction include differential effects of vasopressin depending on the route of administration, the timing of injection, and the presence of aversive effects produced by the neuropeptide.

Vasopressin in the lateral septum regulates pair bond formation in male prairie voles (Microtus ochrogaster)

Male prairie voles (Microtus ochrogaster) form a pair bond with a female partner after mating, and this behavior is regulated by the neuropeptide vasopressin (AVP). The authors report that AVP in the lateral septum is important for pair bond formation. Administration of an AVP V1a receptor antagonist in the lateral septum blocked mating-induced pair bonding, whereas administration of AVP induced this behavior in the absence of mating. In addition, administration of an oxytocin (OT) receptor antagonist in the lateral septum also blocked pair bond formation induced by either mating or AVP administration, suggesting that the OT receptor blockade may have interfered with the AVP regulation of behavior. Together, these data provide evidence suggesting that AVP in the lateral septum regulates pair bond formation in male prairie voles and that this process requires access to both AVP and OT receptors.

IL-1beta immunoreactive neurons in the human hypothalamus: reduced numbers in multiple sclerosis

Corticotropin-releasing hormone (CRH)-containing neurons in the paraventricular nucleus (PVN) in the hypothalamus of multiple sclerosis (MS) patients are hyperactivated. Since interleukin-1 (IL-1)beta is a powerful activator of CRH neurons, its immunohistochemical expression was studied in the postmortem hypothalamus of MS patients (n=11) and matched controls (n=11). Hypothalamic tissue of 10/11 MS patients showed demyelinating lesions that in many cases contained IL-1beta-immunoreactive (ir) macrophages and glial cells. In control subjects IL-1beta-ir was only sporadically found in glial cells. Interestingly, abundant IL-1beta-ir was also present in hypothalamic neurons. Neuronal IL-1beta co-localised with oxytocin and not with vasopressin or CRH. IL-1beta clearly yielded a less intense staining in neurons and numbers of IL-1-ir neurons in the PVN were 4.5-fold reduced in MS. We suggest that IL-1beta produced by activated glial cells in the hypothalamus of MS patients may contribute to the activation of the hypothalamic CRH neurons, while reduced expression of neuronal IL-1beta in MS patients may have consequences for neuroendocrine, behavioural or autonomic functioning.

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.

Differential behavioural effects of chronic infusion of CRH 1 and CRH 2 receptor antisense oligonucleotides into the rat brain

The purpose of this study was to investigate the functional role the two corticotropin-releasing hormone (CRH) receptor subtypes play in regulating the behavioural performance of rats in various well-defined test situations. Antisense oligodeoxynucleotides (ODNs) corresponding to either the rat CRH1 or CRH2 receptor mRNA were infused chronically into the lateral ventricle of male rats via osmotic minipumps (5 microg/0.5 microl/h over 6 days). Control groups received infusions of either a scrambled sequence ODN or mixed bases ODN or vehicle. On day 4 after surgery, the rats were subjected to 10 min of social defeat and immediately afterwards tested on the elevated plus-maze. Compared to a scrambled sequence control ODN, CRH1 receptor antisense ODN infusion was found to exert an anxiolytic-like effect whereas CRH2 receptor antisense ODN infusion had no effect on defeat-induced anxiety-related behaviour. In contrast, the CRH2 receptor antisense ODN increased immobility in a forced swim test whereas CRH1 receptor ODN-treated rats did not differ from controls. No influence of either ODN was found on general locomotor activity in an open field or on short-term memory performance in a social discrimination test. Furthermore, the CRH2 receptor antisense ODN did not affect spatial learning in a Morris water maze task. An additional experiment comparing a mixture of both missense ODNs and a vehicle control group confirmed that the former failed to induce non-specific (toxic) side effects, further substantiating the specificity of the respective antisense effects measured in this study. The results support the hypothesis that the two CRH receptor subtypes selectively mediate differential effects of endogenous CRH or CRH-related peptides at the brain level with the CRHI receptor contributing predominantly to emotional behaviour and the CRH2 receptor being involved in the regulation of stress coping behaviour.

Co-localization of interleukin-1 receptor type I and interleukin-1 receptor antagonist with vasopressin in magnocellular neurons of the paraventricular and supraoptic nuclei of the rat hypothalamus

Interleukin-1 receptor type I and interleukin-1 receptor antagonist were found in magnocellular neurons of the paraventricular and supraoptic nuclei of the rat hypothalamus by immunohistochemical detection. Double-labelling experiments revealed that both proteins occurred in vasopressin-containing neurons. A similar distribution pattern was observed in a group of vasopressin-positive accessory magnocellular neurons. Axons emanating from the interleukin-1 receptor type I- and interleukin-1 receptor antagonist-immunoreactive neuronal cell bodies could be seen within the hypothalamic nuclei, and varicosities expressing interleukin-1 receptor antagonist immunoreactivity were observed in the internal zone of the median eminence, as well as in the hypothalamo-pituitary projection. The co-localization of interleukin-1 receptor type I with vasopressin is in agreement with findings that interleukin-1 has a stimulatory effect on vasopressin synthesis and release. The hypothalamic neurons may serve as a source of interleukin-1 receptor antagonist to balance the effects of interleukin-1.

Central administration of interleukin-1 beta reduces natural killer cell activity in non-pregnant rats, but not in pregnant rats

To examine responses of natural killer cell activity (NKCA) to interleukin-1 beta (IL-1 beta) during pregnancy, we determined splenic NKCA as well as blood and brain indicators in virgin and pregnant rats (14 or 21 days gestation) with intracerebroventricular (i.c.v.) administration of IL-1 beta. NKCA was reduced and blood beta-endorphin (beta EP) was increased with the progress of pregnancy. I.c.v. administration of IL-1 beta reduced NKCA and corticotropin-releasing hormone (CRH) in the median eminence (ME), and increased beta EP in virgin rats, but did not change any parameters in pregnant rats with 21 days gestation. These data suggest that the immunosuppressive effect of central administration of IL-1 beta is blocked by pregnancy. CRH in the ME and opioid system seem to be involved in the inhibitory effect of pregnancy on IL-1 beta-induced immunosuppression.

Different receptor mechanisms mediate the effects of endotoxin and interleukin-1 on female sexual behavior

Activation of the immune system by lipopolysaccharide (LPS) produces physiological, neuroendocrine and behavioral effects, some of which are mediated by cytokine production. We have previously shown that the cytokine interleukin-1 (IL-1) inhibits sexual behavior in female, but not male rats, while producing a comparable suppression of locomotion in both sexes. The present study examined the effects of LPS on sexual behavior and locomotion of male and female rats, and the involvement of IL-1 receptors in mediating the effects of IL-1 and LPS on females' behavior. Peripheral (i.p.) administration of LPS (50 or 250 microg/kg) significantly decreased sexual behavior in females, up to 6 h after administration, while it had no effect on male sexual behavior. However, locomotor activity, measured in the open-field test, was similarly reduced by LPS in both males and females. Pretreatment with the IL-1 receptor antagonist (IL-1ra) either i.p. (10 mg/kg) or intracerebroventricularly (i.c.v.) (50 microg/rat) did not prevent the inhibition of female sexual behavior and locomotion induced by either i.p. (50 microg/kg) or i.c.v. (200 or 400 ng/rat) administration of LPS, respectively. However, identical doses of IL-1ra significantly reversed the effects of IL-1beta, administered either i.p. (5 microg/kg) or i.c.v. (50 ng/rat), respectively. These results demonstrate that both LPS and IL-1beta produce marked inhibition of sexual behavior in female, but not in male rats. However, IL-1 receptors are not required for the effects of LPS on sexual behavior in female rats.

'Quality of life' after therapy in rats with myocardial infarction: dissociation between hemodynamic and behavioral improvement

Rats with myocardial infarction provide a clinically relevant model for hemodynamic and survival studies. Moreover, behavioral changes in this model, i.e. increased anxiety and reduced interest in environment and social interactions, mimic aspects of the reduced quality of life of patients. In the present study, we investigated whether pharmacological treatment that is known to improve hemodynamics and prognosis could also affect the behavioral changes associated with quality of life. Rats with 3-week-old infarcts were treated with intermittent dobutamine (1 mg/kg i.p., twice daily) or captopril (2 milligrams in drinking water). After 2 weeks of treatment, when from previous studies hemodynamics are expected to be restored, behavioral tests were performed. In the free exploration test, which primarily evaluates exploratory behavior, dobutamine normalized the reduced interest in the environment. In the standard open field and social interaction tests, which also include an anxiety component, the beneficial effects of dobutamine were not observed. In contrast, captopril normalized all behavioral changes that indicated increased anxiety. In conclusion, the expected similar hemodynamic improvement with dobutamine and captopril treatment resulted in improvement of different aspects of the changed behavior of rats with myocardial infarction, indicating that there is no direct relationship between hemodynamics and quality of life. The behavioral tests used, in combination with our previously described functional hemodynamic measurements, could provide a new basis for evaluating the effects of therapy on hemodynamic function as well as the quality of life.

Corticosterone controls interleukin-1 beta expression and sickness behavior in the rat

We studied the effect of corticosterone on interleukin (IL)-1 beta synthesis, body temperature, general activity, food consumption and fluid intake in rats treated with bacterial lipopolysaccharide (LPS). Radiotelemetry was used to assess body temperature and locomotor activity in combination with continuous automated recordings of feeding and drinking. This technique was developed as a novel method to identify and measure sickness behavior in rodents. The animals were (a) sham-operated, (b) adrenalectomized or (c) sham-operated and treated with corticosterone (10 mg/kg, subcutaneously). They were then intraperitoneally injected with vehicle or LPS at a dose (100 micrograms/kg) that in sham-operated rats induced fever and anorexia, reduced spontaneous activity and increased IL1-beta mRNA in spleen and adrenals as determined by Northern blot analysis. Adrenalectomized rats produced larger amounts of splenic IL-1 beta mRNA, reduced their general activity much more and developed a mild adipsia as compared with adrenal-intact animals. Administration of corticosterone 1 h before LPS lowered the splenic IL-1 beta mRNA content compared to LPS-treated adrenal-intact rats that did not receive corticosterone and inhibited fever and anorexia, whereas the glucocorticoid did not attenuate the endotoxin-induced suppression of locomotor activity. Our data suggest that during inflammatory conditions body temperature, sickness behavior and the synthesis of IL-1 beta are controlled by corticosterone. Different components of sickness behavior seem to be independently regulated and are under differential control by glucocorticoids.

On the Inseparability of Mental and Physical Health in Aged Persons: Lessons From Depression and Medical Comorbidity

Recent research findings demonstrate that general medical and mental health are inseparable in older individuals. The medical consequences of depression can be summarized with the unifying hypothesis that depression interacts with medical or neurological illness to modify the course of disease and to amplify its associated effects. The medical causes of depression can be divided into specific mechanisms of certain diseases or medications and general mechanisms that may integrate effects of a number of the common chronic disorders of late life. The authors discuss two general hypotheses: One suggests that depression may be associated with subclinical cerebrovascular disease in older patients with cerebrovascular risk factors; the other suggests that depression occurring in association with various conditions may be related to cytokine-mediated "sickness behavior." The research literature makes a compelling case for the need to address psychiatric-medical comorbidity in late life as a central issue in public policy and the design of health care systems.

Chronic infusion of a CRH1 receptor antisense oligodeoxynucleotide into the central nucleus of the amygdala reduced anxiety-related behavior in socially defeated rats

We studied the role of central amygdala CRH receptors in behavioral responses to an anxiogenic stimulus. An antisense oligodeoxynucleotide corresponding to the rat CRH1 receptor mRNA was infused chronically into the central amygdaloid nucleus of male rats via osmotic minipumps (0.25 micrograms/0.5 microliters/h). Control groups received infusions of either a scrambled sequence oligodeoxynucleotide or vehicle. On the 4th day of treatment, rats were subjected to 10 min of social defeat and immediately afterwards tested on the elevated plus-maze. Antisense oligodeoxynucleotide-treated rats spent significantly more time exploring the open arms of the plus-maze than scrambled sequence- and vehicle-treated animals, both of which did not differ from each other. The social discrimination test, on the other hand, revealed no difference in juvenile recognition abilities among the treatment groups. Using in situ hybridization and receptor autoradiography, we were not able to detect clear signals of CRH1 receptor mRNA and CRH binding sites in the central amygdaloid nucleus of either group, confirming the reportedly low expression and density of CRH receptors in this brain area. The present data support the view that CRH receptors in the central nucleus of the amygdala are involved in the mediation and expression of anxiety-related behavior, but simultaneously raise questions as to the mechanisms of antisense oligodeoxynucleotide action.

Differential effects of IL-1ra on sickness behavior and weight loss induced by IL-1 in rats

Peripheral and central injections of recombinant human interleukin-1 beta (IL-1 beta) have been shown to decrease social exploration and to induce body weight loss in rats. To characterize the receptor mechanisms of these effects, we used as a tool a specific antagonist of the receptors of IL-1, IL-1ra. Intraperitoneal (i.p.) administration of IL-1ra (8 mg/kg) blocked the effect of i.p. injection of IL-1 beta (4 micrograms/rat) on social behaviour but not on body weight. Central administration of IL-1ra (60 micrograms/rat, i.c.v.) abrogated the effects of centrally administered IL-1 beta (30 ng/rat, i.c.v.) on both social behaviour and body weight. Central injection of IL-1ra (4 micrograms/rat, i.c.v.) also attenuated the effects of i.p. administered IL-1 beta (4 micrograms/rat) on social behaviour but not on body weight. These results suggest that the effects of IL-1 beta on social behavior are mediated centrally and that its effect on the loss of body weight involves different receptor mechanisms.

Interleukin-1 beta stimulates both central and peripheral release of vasopressin and oxytocin in the rat

Simultaneous microdialysis in the brain and blood was used to monitor the release of vasopressin and oxytocin within the hypothalamic supraoptic (SON) and paraventricular (PVN) nuclei and into the systemic circulation of urethane-anaesthetized male rats before and after central administration of interleukin-1 beta (IL-1 beta). Following intracerebroventricular infusion of the cytokine (200 ng/5 microliters), the content of vasopressin (up to 278% compared to vehicle-treated control, P < 0.01 compared to vehicle-treated control and preinfusion baseline) but not oxytocin (up to 148%, not significant) in 30-min blood microdialysates was found to be increased. This peripheral release was accompanied by a transient rise in vasopressin (up to 163%, P < 0.05) and oxytocin (up to 182%, P < 0.05) release within the SON, the peak typically occurring during the first and second 30-min collection intervals after IL-1 beta respectively. In contrast, in the simultaneously microdialysed PVN, both vasopressin and oxytocin failed to respond to intracerebroventricular IL-1 beta. In another series of experiments, IL-1 beta was directly infused (20 ng/0.5 microliters) into either the SON or PVN during microdialysis of the corresponding nucleus. The cytokine caused a significant and immediate rise in intra-SON release of both vasopressin (up to 225%, P < 0.01) and oxytocin (up to 178%, P < 0.05). Again, in the PVN, nonapeptide release, although tending to be stimulated in response to intranuclear IL-1 beta, failed to reach statistical significance. The cytokine-induced central and peripheral release pattern appeared to be independent of the rise in body temperature observed after IL-1 beta administration.(ABSTRACT TRUNCATED AT 250 WORDS)

Interleukin-1 induces sleep-like behavior and alters call structure in juvenile rhesus macaques

To date, there have been no investigations of the behavioral effects of interleukin-1 (IL-1) in nonhuman primates. In this study the locomotor behavior and vocalizations of juvenile rhesus monkeys were monitored for 45 minutes following intravenous injections of recombinant human IL-1 alpha. In addition, their reaction to a broadcasted recording of infant monkey distress calls was determined 20 minutes after the beginning of each test session. IL-1 induced sleep-like inactivity and significantly diminished the monkey's behavioral and vocal responses to the broadcasted calls. The coo calls uttered by the monkeys following IL-1 treatment also had a longer duration and lower fundamental frequency than calls during the control condition. As several studies have indicated that behavioral effects of IL-1 may be mediated by corticotropin-releasing hormone (CRH), a second group of rhesus monkeys was given injections of CRH. CRH did not alter behavior or call structure at the dose administered. These results extend previous research on the behavioral effects of IL-1 to include the nonhuman primate and provide the first evidence that cytokines can affect vocal communication in rhesus monkeys. © 1995 Wiley-Liss, Inc.

Behavioral changes following chronic myocardial infarction in rats

Myocardial infarction evokes major physiological changes because of the acute loss of functional cardiac tissue, resulting in more or less severe symptoms of congestive heart failure. In addition, general well-being of patients, their quality of life, is reduced. This includes anxiety/depression, loss of interest in environment and social interactions, sexual problems, and sleep disturbances. Postinfarction treatment is aimed mainly at improving life expectancy, whereas less attention is paid to the quality of that life. The aim of the present study was to determine behavioral changes after myocardial infarction in a (otherwise proven as clinically relevant) rat model for heart failure after myocardial infarction. We have chosen for behavioral tests based upon certain aspects of quality of life in patients. Anxiety/depression, interest in environment, and mobility, tested in an open field, revealed that infarcted rats are more anxious (as inferred from a higher preference for the safe corner area and less visits to the middle area), have less interest in a new environment [as indicated by less exploratory behavior and a longer time before they go into the new area (free exploration)], and showed less mobility (as indicated by reduced distance walked and less time spent on walking). In a test on social interaction, infarcted rats spent less time on social behavior and displayed even somewhat more walking away, suggesting active avoidance of social interaction. The observed behavioral changes in infarcted rats match very well with the aspects of reduced quality of life in postinfarct patients.(ABSTRACT TRUNCATED AT 250 WORDS)

Characterization of cytokine-induced hyperalgesia

Agents which induce symptoms of illness, such as lipopolysaccharide (LPS), cause diverse effects including hyperalgesia. While previous studies have examined central pathways mediating LPS hyperalgesia, the initial steps in activating this system remain unknown. Since LPS induces the release of various cytokines and eicosinoids from immune cells, the present series of experiments examined the potential involvement of these substances in LPS hyperalgesia. This work demonstrates that: (a) Interleukin-1 beta (IL-1 beta) can produce hyperalgesia following either intraperitoneal or intracerebroventricular injection. In contrast, IL-1 beta delivered intrathecally did not affect pain responsivity. (b) Liver macrophages (Kupffer cells) appear to be critically involved, and relay signals to the brain via hepatic vagal afferents. (c) Both IL-1 beta and tumor necrosis factor appear to be critical mediators of LPS hyperalgesia. In contrast, prostaglandins do not appear to be involved. Taken together, these studies suggest that substances classically thought of as products of the immune system may dynamically enhance pain responsivity via actions either on the hepatic vagus or at central sites.

Role of the vomeronasal system in vasopressinergic modulation of social recognition in rats

To assess the role of the vomeronasal organ (VNO) in the dependence of social recognition on vasopressinergic transmission, vomerectomized rats were compared to intact and castrated male rats. Removal of the VNO significantly decreased the duration of social investigation and temporarily impaired social recognition. In contrast to sham-operated animals and non-operated animals, lesioned rats were no longer responsive to the blocking effect of the antagonist of the vasopressor receptors of vasopressin (dPTyr(Me)AVP, 30 micrograms/kg subcutaneously) on social recognition. Consequently, VNO-lesioned rats behave like castrates, in spite of the lack of effect of removal of the VNO on plasma testosterone levels. These results suggest that androgen-dependent vasopressinergic neurons are part of the VNO pathway and that the VNO system is important for processing and storage of socially relevant information in male rat.

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.

Different receptor mechanisms mediate the pyrogenic and behavioral effects of interleukin 1

Interleukin 1 (IL-1) is a cytokine released during immune activation that mediates the host's response to infection and inflammation. Peripheral and central injections of IL-1 induce fever and sickness behavior, including decreased food motivation and reduced interest in social activities. To determine the receptor mechanisms responsible for these effects, rats were injected with IL-1 receptor antagonist (IL-1ra), an endogenous cytokine that acts as a pure antagonist of IL-1 receptors. IL-1ra blocked the increased body temperature and oxygen consumption induced by injection of recombinant human IL-1 only when both cytokines were administered i.p. In contrast, i.p. or intracerebroventricular administration of IL-1ra blocked the depressive effect of IL-1 beta on food-motivated behavior and social exploration when this cytokine was administered by the same route as the antagonist. In addition, intracerebroventricular IL-1ra blocked the reduction in social exploration produced by i.p. IL-1 beta but had only partial antagonist effects on the decrease in food-motivated behavior induced by i.p. IL-1 beta. In each case, the dose of IL-1ra was 100- to 1000-fold in excess of the biologically active dose of IL-1. These results suggest that the receptor mechanisms that mediate the behavioral and pyrogenic effects of IL-1 are heterogeneous.

Mechanisms of the behavioral effects of interleukin 1. Role of prostaglandins and CRF

Sickness behavior induced by IL-1 can be assessed quantitatively by measuring disruption of schedule-controlled behavior and loss of interest in social activities displayed by rats or mice injected peripherally or centrally with this monokine. These effects are mediated via the release of prostaglandins since they are blocked by the prostaglandin synthesis inhibitors indomethacin and piroxicam. They do not depend, however, on the central release of CRF, since they are not altered by central administration of either CRF or the specific antagonist of CRF receptors.