Modulation of behavioral and neurochemical measures of forebrain dopamine function in mice by species-specific interleukin-2

Immune and glial cell alterations in the rat brain after repeated exposure to the synthetic cannabinoid JWH-018

The use of synthetic cannabinoid receptor agonists (SCRAs) poses major psychiatric risks. We previously showed that repeated exposure to the prototypical SCRA JWH-018 induces alterations in dopamine (DA) transmission, abnormalities in the emotional state, and glial cell activation in the mesocorticolimbic DA circuits of rats. Despite growing evidence suggesting the relationship between substance use disorders (SUD) and neuroinflammation, little is known about the impact of SCRAs on the neuroimmune system. Here, we investigated whether repeated JWH-018 exposure altered neuroimmune signaling, which could be linked with previously reported central effects. Adult male Sprague-Dawley (SD) rats were exposed to JWH-018 (0.25 mg/kg, i.p.) for fourteen consecutive days, and the expression of cytokines, chemokines, and growth factors was measured seven days after treatment discontinuation in the striatum, cortex, and hippocampus. Moreover, microglial (ionized calcium-binding adaptor molecule 1, IBA-1) and astrocyte (glial fibrillary acidic protein, GFAP) activation markers were evaluated in the caudate-putamen (CPu). Repeated JWH-018 exposure induces a perturbation of neuroimmune signaling specifically in the striatum, as shown by increased levels of cytokines [interleukins (IL) -2, -4, -12p70, -13, interferon (IFN) γ], chemokines [macrophage inflammatory protein (MIP) -1α, -3α], and growth factors [macrophage colony-stimulating factor (M-CSF), vascular endothelial growth factor (VEGF)], together with increased IBA-1 and GFAP expression in the CPu. JWH-018 exposure induces persistant brain region-specific immune alterations up to seven days after drug discontinuation, which may contribute to the behavioral and neurochemical dysregulations in striatal areas that play a role in the reward-related processes that are frequently impaired in SUD.

Assessing causal relationship between circulating cytokines and age-related neurodegenerative diseases: a bidirectional two-sample Mendelian randomization analysis

Numerous studies have reported that circulating cytokines (CCs) are linked to age-related neurodegenerative diseases (ANDDs); however, there is a lack of systematic investigation for the causal association. A two-sample bidirectional Mendelian Randomisation (MR) method was utilized to evaluate the causal effect. We applied genetic variants correlated with concentrations of CCs from a genome-wide association study meta-analysis (n = 8293) as instrumental variables. Summary data of three major ANDDs [Alzheimer's disease (AD), Parkinson's disease (PD), and Amyotrophic lateral sclerosis (ALS)] were identified from the IEU OpenGWAS platform (n = 627, 266). Inverse-variance weighted method is the main approach to analyse causal effect, and MR results are verified by several sensitivity and pleiotropy analyses. In directional MR, it suggested that several CCs were nominally correlated with the risk of ANDDs, with a causal odds ratio (OR) of Interleukin (IL)-5 of 0.909 for AD; OR of IL-2 of 1.169 for PD; and OR of Beta nerve growth factor of 1.142 for ALS). In reverse MR, there were some suggestively causal effects of ANDDs on CCs (AD on increased Basic fibroblast growth factor and IL-12 and decreased Stem cell growth factor beta; PD on decreased Monokine induced by interferon-gamma; ALS on decreased Basic fibroblast growth factor and IL-17). The findings were stable across sensitivity and pleiotropy analyses. However, after Bonferroni correction, there is no statistically significant association between CCs and ANDDs. Through the genetic epidemiological approach, our study assessed the role and presented possible causal associations between CCs and ANDDs. Further studies are warranted to verify the causal associations.

Dopamine Transmission Imbalance in Neuroinflammation: Perspectives on Long-Term COVID-19

Dopamine (DA) is a key neurotransmitter in the basal ganglia, implicated in the control of movement and motivation. Alteration of DA levels is central in Parkinson’s disease (PD), a common neurodegenerative disorder characterized by motor and non-motor manifestations and deposition of alpha-synuclein (α-syn) aggregates. Previous studies have hypothesized a link between PD and viral infections. Indeed, different cases of parkinsonism have been reported following COVID-19. However, whether SARS-CoV-2 may trigger a neurodegenerative process is still a matter of debate. Interestingly, evidence of brain inflammation has been described in postmortem samples of patients infected by SARS-CoV-2, which suggests immune-mediated mechanisms triggering the neurological sequelae. In this review, we discuss the role of proinflammatory molecules such as cytokines, chemokines, and oxygen reactive species in modulating DA homeostasis. Moreover, we review the existing literature on the possible mechanistic interplay between SARS-CoV-2-mediated neuroinflammation and nigrostriatal DAergic impairment, and the cross-talk with aberrant α-syn metabolism.

Preventive exercise attenuates IL-2-driven mood disorders in multiple sclerosis

BACKGROUND

Elevated levels of specific proinflammatory molecules in the cerebrospinal fluid (CSF) have been associated with disability progression, enhanced neurodegeneration and higher incidence of mood disorders in people with multiple sclerosis (MS). Studies in animal models of MS suggest that preventive exercise may play an immunomodulatory activity, with beneficial effects on both motor deficits and behavioral alterations. Here we explored the impact of lifestyle physical activity on clinical presentation and associated central inflammation in a large group of newly diagnosed patients with MS. Furthermore, we addressed the causal link between exercise-mediated immunomodulation and mood symptoms in the animal setting.

METHODS

A cross-sectional study was conducted on 235 relapsing-remitting MS patients at the time of the diagnosis. Patients were divided into 3 groups ("sedentary", "lifestyle physical activity" and "exercise") according to the level of physical activity in the six months preceding the evaluation. Patients underwent clinical, neuropsychological and psychiatric evaluation, magnetic resonance imaging and lumbar puncture for diagnostic purposes. The CSF levels of proinflammatory and anti-inflammatory cytokines were analyzed and compared with a group of 80 individuals with non-inflammatory and non-degenerative diseases. Behavioral and electrophysiological studies were carried out in control mice receiving intracerebral injection of IL-2 or vehicle. Behavior was also assessed in mice with experimental autoimmune encephalomyelitis (EAE), animal model of MS, reared in standard (sedentary group) or running wheel-equipped (exercise group) cages.

RESULTS

In exercising MS patients, depression and anxiety were reduced compared to sedentary patients. The CSF levels of the interleukin-2 and 6 (IL-2, IL-6) were increased in MS patients compared with control individuals. In MS subjects exercise was associated with normalized CSF levels of IL-2. In EAE mice exercise started before disease onset reduced both behavioral alterations and striatal IL-2 expression. Notably, a causal role of IL-2 in mood disorders was shown. IL-2 administration in control healthy mice induced anxious- and depressive-like behaviors and impaired type-1 cannabinoid (CB1) receptor-mediated neurotransmission at GABAergic synapses, mimicking EAE-induced synaptic dysfunction.

CONCLUSIONS

Our results indicate an immunomodulatory effect of exercise in MS patients, associated with reduced CSF expression of IL-2, which might result in reduced mood disorders. These data suggest that exercise in the early stages may act as a disease-modifying therapy in MS although further longitudinal studies are needed to clarify this issue.

Toxoplasmosis: Targeting neurotransmitter systems in psychiatric disorders

The most common form of the disease caused by Toxoplasma gondii (T. gondii) is latent toxoplasmosis due to the formation of tissue cysts in various organs, such as the brain. Latent toxoplasmosis is probably a risk factor in the development of some neuropsychiatric disorders. Behavioral changes after infection are caused by the host immune response, manipulation by the parasite, central nervous system (CNS) inflammation, as well as changes in hormonal and neuromodulator relationships. The present review focused on the exact mechanisms of T. gondii effect on the alteration of behavior and neurotransmitter levels, their catabolites and metabolites, as well as the interaction between immune responses and this parasite in the etiopathogenesis of psychiatric disorders. The dysfunction of neurotransmitters in the neural transmission is associated with several neuropsychiatric disorders. However, further intensive studies are required to determine the effect of this parasite on altering the level of neurotransmitters and the role of neurotransmitters in the etiology of host behavioral changes.

Sex differences and similarities in the neuroimmune response to central administration of poly I:C

BACKGROUND

The neuroimmune system is required for normal neural processes, including modulation of cognition, emotion, and adaptive behaviors. Aberrant neuroimmune activation is associated with dysregulation of memory and emotion, though the precise mechanisms at play are complex and highly context dependent. Sex differences in neuroimmune activation and function further complicate our understanding of its roles in cognitive and affective regulation.

METHODS

Here, we characterized the physiological sickness and inflammatory response of the hippocampus following intracerebroventricular (ICV) administration of a synthetic viral mimic, polyinosinic:polycytidylic acid (poly I:C), in both male and female C57Bl/6N mice.

RESULTS

We observed that poly I:C induced weight loss, fever, and elevations of cytokine and chemokines in the hippocampus of both sexes. Specifically, we found transient increases in gene expression and protein levels of IL-1α, IL-1β, IL-4, IL-6, TNFα, CCL2, and CXCL10, where males showed a greater magnitude of response compared with females. Only males showed increased IFNα and IFNγ in response to poly I:C, whereas both males and females exhibited elevations of IFNβ, demonstrating a specific sex difference in the anti-viral response in the hippocampus.

CONCLUSION

Our data suggest that type I interferons are one potential node mediating sex-specific cytokine responses and neuroimmune effects on cognition. Together, these findings highlight the importance of using both males and females and analyzing a broad set of inflammatory markers in order to identify the precise, sex-specific roles for neuroimmune dysregulation in neurological diseases and disorders.

Increased Retinal Ganglion Cell Survival by Exogenous IL-2 Depends on IL-10, Dopamine D1 Receptors, and Classical IL-2/IL-2R Signaling Pathways

Interleukin-2 (IL-2) is a classical pro-inflammatory cytokine known to display neuroprotective roles in the central nervous system including the retina. In the present study, we investigate the molecular targets involved in the neurotrophic effect of IL-2 on retinal ganglion cells (RGC) after optic nerve axotomy. Analysis of retrograde labeling of RGC showed that common cell survival mediators, as Trk receptors, Src, PI3K, PKC, and intracellular calcium do not mediate the neurotrophic effect of IL-2 on RGC. No involvement of MAPK p38 was also observed. However, other MAPKs as MEK and JNK appear to be mediating this IL-2 effect. Our data also indicate that JAK2/3 are important intracellular proteins for the IL-2 effect. Interestingly, we demonstrate that the IL-2 effect depends on dopamine D1 receptors (D1R), the cAMP/PKA pathway, interleukin-10 (IL-10), and NF-κB, suggesting that RGC survival induced by IL-2 encompasses a molecular network of major complexity. In addition, treatment of retinal cells with recombinant IL-10 or 6-Cl-pb (D1R full agonist) was able to increase RGC survival similar to IL-2. Taken together, our results suggest that after optic nerve axotomy, the increase in RGC survival triggered by IL-2 is mediated by IL-10 and D1R along with the intracellular pathways of MAPKs, JAK/STAT, and cAMP/PKA.

Cyclooxygenase Inhibition Safety and Efficacy in Inflammation-Based Psychiatric Disorders

According to the World Health Organization, the major psychiatric and neurodevelopmental disorders include major depression, bipolar disorder, schizophrenia, and autism spectrum disorder. The potential role of inflammation in the onset and progression of these disorders is increasingly being studied. The use of non-steroidal anti-inflammatory drugs (NSAIDs), well-known cyclooxygenase (COX) inhibitors, combined with first-choice specific drugs have been long investigated. The adjunctive administration of COX inhibitors to classic clinical treatments seems to improve the prognosis of people who suffer from psychiatric disorders. In this review, a broad overview of the use of COX inhibitors in the treatment of inflammation-based psychiatric disorders is provided. For this purpose, a critical analysis of the use of COX inhibitors in the last ten years of clinical trials of the major psychiatric disorders was carried out.

The Relationship Between Serum Cytokine Levels and the Degree of Psychosis and Cognitive Impairment in Patients With Methamphetamine-Associated Psychosis in Chinese Patients

Background: Cytokine levels can be changed in methamphetamine (METH) use disorders (MUDs) and primary psychosis. The present study assessed serum levels of some kinds of interleukins (ILs) in METH-associated psychosis (MAP) and their relationships with psychotic symptoms and cognitive dysfunction. Methods: Serum IL-2R, IL-6, IL-8, and IL-10 levels were examined by chemiluminescence assays in MAP patients (n = 119) and healthy controls (n = 108). The Positive and Negative Syndrome Scale (PANSS) and Montreal Cognitive Assessment (MOCA) were administered. Results: Serum levels of IL-6 and IL-8 were significantly increased in MAP patients (all p < 0.05). There was a negative relationship between IL-2R levels and PANSS positive (P) subscale scores (r = -0.193, p = 0.035). IL-6, IL-8 and IL-10 levels were all negatively correlated with the naming, delayed recall and orientation subscores on the MOCA (r = -0.209, p = 0.022; r = -0.245, p = 0.007; r = -0.505, p < 0.001, respectively). Conclusions: Our results indicate that immune disturbances are related to MAP and that IL-2R, IL-6, IL-8, and IL-10 are associated with the severity of psychotic symptoms and cognitive function impairment.

Are CB2 Receptors a New Target for Schizophrenia Treatment?

Schizophrenia is a complex disorder that involves several neurotransmitters such as dopamine, glutamate, and GABA. More recently, the endocannabinoid system has also been associated with this disorder. Although initially described as present mostly in the periphery, cannabinoid type-2 (CB2) receptors are now proposed to play a role in several brain processes related to schizophrenia, such as modulation of dopaminergic neurotransmission, microglial activation, and neuroplastic changes induced by stress. Here, we reviewed studies describing the involvement of the CB2 receptor in these processes and their association with the pathophysiology of schizophrenia. Taken together, these pieces of evidence indicate that CB2 receptor may emerge as a new target for the development of antipsychotic drugs.

The role of IL-6 in neurodevelopment after prenatal stress

Prenatal stress exposure is associated with adverse psychiatric outcomes, including autism and ADHD, as well as locomotor and social inhibition and anxiety-like behaviors in animal offspring. Similarly, maternal immune activation also contributes to psychiatric risk and aberrant offspring behavior. The mechanisms underlying these outcomes are not clear. Offspring microglia and the pro-inflammatory cytokine interleukin-6 (IL-6), known to influence microglia, may serve as common mechanisms between prenatal stress and prenatal immune activation. To evaluate the role of prenatal IL-6 in prenatal stress, microglia morphological analyses were conducted at embryonic days 14 (E14), E15, and in adult mice. Offspring microglia and behavior were evaluated after repetitive maternal restraint stress, repetitive maternal IL-6, or maternal IL-6 blockade during stress from E12 onwards. At E14, novel changes in cortical plate embryonic microglia were documented-a greater density of the mutivacuolated morphology. This resulted from either prenatal stress or IL-6 exposure and was prevented by IL-6 blockade during prenatal stress. Prenatal stress also resulted in increased microglia ramification in adult brain, as has been previously shown. As with embryonic microglia, prenatal IL-6 recapitulated prenatal stress-induced changes in adult microglia. Furthermore, prenatal IL-6 was able to recapitulate the delay in GABAergic progenitor migration caused by prenatal stress. However, IL-6 mechanisms were not necessary for this delay, which persisted after prenatal stress despite IL-6 blockade. As we have previously demonstrated, behavioral effects of prenatal stress in offspring, including increased anxiety-like behavior, decreased sociability, and locomotor inhibition, may be related to these GABAergic delays. While adult microglia changes were ameliorated by IL-6 blockade, these behavioral changes were independent of IL-6 mechanisms, similar to GABAergic delays. This and previous work from our laboratory suggests that multiple mechanisms, including GABAergic delays, may underlie prenatal stress-linked deficits.

Enrichment pathway analysis. The inflammatory genetic background in Bipolar Disorder

INTRODUCTION

The pathophysiology of Bipolar Disorder (BD) is yet to be fully characterized. In the last years attention was focused on neurodevelopment or neurodegenerative events. In this context, hyper- and hypo- activation of inflammatory cascades may play a role in modulating the architecture and function of neuronal tissues. In the present paper we tested the enrichment of molecular pathways related to inflammatory cascades (IL-1, IL-2, IL-6, IL-8, TNF and INF) testing whether genes related to these systems hold more variations associated with the risk for BD than expected.

METHODS

~7000 bipolar patients and controls with genome-wide data available from NIMH dataset were analyzed. SNPs were imputed, checked for quality control, pruned and tested for association (0.01<p). Fisher test was conducted to test the enrichment within the pathways and the association was permutated (10(5) times) to limit false positive findings.

RESULTS

As a result, IL-6, IL-8 and IFN related pathways held twice to thrice the number of expected variants associated with BD. These tests resisted the permutation analysis.

LIMITATIONS

The restricted number of inflammatory components included in the analysis and the lack of functional consequences for some of the SNPs analyzed may be biased; however, these choices helped the authors to lighten the statistical computational load for the analyses and at the same time included possibly hidden SNPs in linkage disequilibrium with the analyzed variations.

CONCLUSIONS

We bring evidence that the inflammatory cascades may be genetically varied in Bipolar patients. This genetic background may explain part of the pathophysiology of the disorder.

Altered IL-2, IL-6 and IL-8 serum levels in schizophrenia patients with tardive dyskinesia

Immune deregulation has been postulated to be one of the mechanisms underlying the pathogenesis of tardive dyskinesia (TD). We hypothesized that interleukins would have a link with TD in schizophrenia patients. In this study, the serum IL-2, IL-6 and IL-8 levels were examined by enzyme-linked immunosorbent assay (ELISA) in schizophrenia patients with TD (n=48) and without TD (n=45), and healthy controls (n=44). The psychopathological symptoms of schizophrenia were assessed by the Positive and Negative Syndrome Scale (PANSS). The severity of TD was evaluated using Abnormal Involuntary Movement Scale (AIMS). The results showed that serum IL-2, IL-6 and IL-8 levels were significantly different among schizophrenia patients with TD and without TD and normal controls. Moreover, IL-2 level was significantly correlated with PANSS positive subscale and general subscale in patients with TD and without TD. In addition, IL-2 level was positively correlated with AIMS score in TD patients. The results supported that immune disturbance is related to the schizophrenia patients, especially to the patients with TD and ILs might play an important role in the pathophysiology of schizophrenia patients with TD.

Seropositivity and serointensity of Toxoplasma gondii antibodies and DNA among patients with schizophrenia

The aim of this cross sectional case control study was to examine the serofrequency and serointensity of Toxoplasma gondii (Tg) IgG, IgM, and DNA among patients with schizophrenia. A total of 101 patients with schizophrenia and 55 healthy controls from Sungai Buloh Hospital, Selangor, Malaysia and University Malaya Medical Center (UMMC) were included in this study. The diagnosis of schizophrenia was made based on the Diagnostic and Statistical Manual of Mental Disorders, Fourth Edition (DSM-IV). The presence of Tg infection was examined using both indirect (ELISA) and direct (quantitative real-time PCR) detection methods by measuring Tg IgG and IgM and DNA, respectively. The serofrequency of Tg IgG antibodies (51.5%, 52/101) and DNA (32.67%, 33/101) among patients with schizophrenia was significantly higher than IgG (18.2%, 10/55) and DNA (3.64%, 2/55) of the controls (IgG, P=0.000, OD=4.8, CI=2.2-10.5; DNA, P=0.000, OD=12.9, CI=2.17-10.51). However, the Tg IgM antibody between patients with schizophrenia and controls was not significant (P>0.005). There was no significant difference (P>0.005) in both serointensity of Tg IgG and DNA between patients with schizophrenia and controls. These findings have further demonstrated the strong association between the active Tg infection and schizophrenia.

Modulatory effects of proinflammatory cytokines for action cascading processes - evidence from neurosarcoidosis

Neurosarcoidosis is a rare central nervous system manifestation of sarcoidosis. T cell, T-helper cell and macrophage activation via the major histocompatibility complex (MHC) II-mediated pathway causes this disease. Little is known about the possible cognitive disturbances in this disease as most reported instances are case studies. Here, we provide the first in-depth analysis of psychomotor functions in a sample of 30 neurosarcoidosis patients. We investigated action control processes using a paradigm that is able to examine how different tasks are cascaded to achieve the task goal. We integrated electrophysiological (EEG) data with behavioural and neuroimmunological data. Our results show that there was no general cognitive decline in patients with neurosarcoidosis. Patients only presented deficits when two response options have to be prioritized. Patients apply an inefficient processing strategy where they try to processes different response options in parallel. The electrophysiological data show that the deficits are due to dysfunctions at the response selection stage. Behavioural and neurophysiological changes are predictable on the basis of soluble interleukin 2 receptor serum concentrations. The results show that neurosarcoidosis is not associated with nonspecific changes in cognitive functions but does lead to specific alterations in cognitive control that are strongly dependent on immunological parameters.

Inflammatory cytokine-associated depression

Inflammatory cytokines can sometimes trigger depression in humans, are often associated with depression, and can elicit some behaviors in animals that are homologous to major depression. Moreover, these cytokines can affect monoaminergic and glutamatergic systems, supporting an overlapping pathoetiology with major depression. This suggests that there could be a specific major depression subtype, inflammatory cytokine-associated depression (ICAD), which may require different therapeutic approaches. However, most people do not develop depression, even when exposed to sustained elevations in inflammatory cytokines. Thus several vulnerabilities and sources of resilience to inflammation-associated depression have been identified. These range from genetic differences in neurotrophic and serotonergic systems to sleep quality and omega-3 fatty acid levels. Replicating these sources of resilience as treatments could be one approach for preventing "ICAD". This article is part of a Special Issue entitled SI: Neuroimmunology in Health And Disease.

Latent Toxoplasma gondii infection leads to improved action control

The parasite Toxoplasma gondii has been found to manipulate the behavior of its secondary hosts to increase its own dissemination which is commonly believed to be to the detriment of the host (manipulation hypothesis). The manipulation correlates with an up-regulation of dopaminergic neurotransmission. In humans, different pathologies have been associated with T. gondii infections but most latently infected humans do not seem to display overt impairments. Since a dopamine plus does not necessarily bear exclusively negative consequences in humans, we investigated potential positive consequences of latent toxoplasmosis (and the presumed boosting of dopaminergic neurotransmission) on human cognition and behavior. For this purpose, we focused on action cascading which has been shown to be modulated by dopamine. Based on behavioral and neurophysiological (EEG) data obtained by means of a stop-change paradigm, we were able to demonstrate that healthy young humans can actually benefit from latent T. gondii infection as regards their performance in this task (as indicated by faster response times and a smaller P3 component). The data shows that a latent infection which is assumed to affect the dopaminergic system can lead to paradoxical improvements of cognitive control processes in humans.

A potential association between Toxoplasma gondii infection and schizophrenia in mouse models

Schizophrenia is a serious neuropsychiatric disease of uncertain etiology, which causes human mental disorder and affects about 1% of the population. In recently years, some studies showed that some cases of schizophrenia may be associated with Toxoplasma gondii infection. In order to investigate a potential association between Toxoplasma infection and schizophrenia, we investigated the relative clinical symptom of schizophrenia such as learning and memory capability, depression and stereotypy to find some useful information by behavioral test in mouse models. Our results demonstrated that mice from Toxoplasma infection and MK-801 administration (as the model of schizophrenia) were impaired in learning and memory capability, and they had more serious depression and stereotypy compared with the control mice, especially the mice from congenital Toxoplasma infection. In addition, our results clearly showed that the number of cysts in brain tissue of congenital Toxoplasma infection mice was significantly low than in acquired Toxoplasma infected mice. Collectively, these results suggested a potential association between Toxoplasma infection and schizophrenia.

Selective Neuronal and Brain Regional Expession of IL-2 in IL2P 8-GFP Transgenic Mice: Relation to Sensorimotor Gating

Brain-derived interleukin-2 (IL-2) has been implicated in diseases processes that arise during CNS development (e.g., autism) to neurodegenerative alterations involving neuroinflammation (e.g., Alzheimer’s disease). Progress has been limited, however, because the vast majority of current knowledge of IL-2’s actions on brain function and behavior is based on the use exogenously administered IL-2 to make inferences about the function of the endogenous cytokine. Thus, to identify the cell-type(s) and regional circuitry that express brain-derived IL-2, we used B6.Cg-Tg/ IL2-EGFP17Evr (IL2p8-GFP) transgenic mice, which express green fluorescent protein (GFP) in peripheral immune cells known to produce IL-2. We found that the IL2-GFP transgene was localized almost exclusively to NeuN-positive cells, indicating that the IL-2 is produced primarily by neurons. The IL2-GFP transgene was expressed in discrete nuclei throughout the rostral-caudal extent of the brain and brainstem, with the highest levels found in the cingulate, dorsal endopiriform nucleus, lateral septum, nucleus of the solitary tract, magnocellular/gigantocellular reticular formation, red nucleus, entorhinal cortex, mammilary bodies, cerebellar fastigial nucleus, and posterior interposed nucleus. Having identified IL-2 gene expression in brain regions associated with the regulation of sensorimotor gating (e.g., lateral septum, dorsal endopiriform nucleus, entorhinal cortex, striatum), we compared prepulse inhibition (PPI) of the acoustic startle response in congenic mice bred in our lab that have selective loss of the IL-2 gene in the brain versus the peripheral immune system, to test the hypothesis that brain-derived IL-2 plays a role in modulating PPI. We found that congenic mice devoid of IL-2 gene expression in both the brain and the peripheral immune system, exhibited a modest alteration of PPI. These finding suggest that IL2p8-GFP transgenic mice may be a useful tool to elucidate further the role of brain-derived IL-2 in normal CNS function and disease.

Cytokines, neurophysiology, neuropsychology, and psychiatric symptoms

Recent research has overcome the old paradigms of the brain as an immunologically privileged organ, and of the exclusive role of neurotransmitters and neuropeptides as signal transducers in the central nervous system. Growing evidence suggests that the signal proteins of the immune system - the cytokines - are also involved in modulation of behavior and induction of psychiatric symptoms. This article gives an overview on the nature of cytokines and the proposed mechanisms of immune-to-brain interaction. The role of cytokines in psychiatric symptoms, syndromes, and disorders like sickness behavior, major depression, and schizophrenia are discussed together with recent immunogenetic findings.

The role of parasites and pathogens in influencing generalised anxiety and predation-related fear in the mammalian central nervous system

Behavioural and neurophysiological traits and responses associated with anxiety and predation-related fear have been well documented in rodent models. Certain parasites and pathogens which rely on predation for transmission appear able to manipulate these, often innate, traits to increase the likelihood of their life-cycle being completed. This can occur through a range of mechanisms, such as alteration of hormonal and neurotransmitter communication and/or direct interference with the neurons and brain regions that mediate behavioural expression. Whilst some post-infection behavioural changes may reflect 'general sickness' or a pathological by-product of infection, others may have a specific adaptive advantage to the parasite and be indicative of active manipulation of host behaviour. Here we review the key mechanisms by which anxiety and predation-related fears are controlled in mammals, before exploring evidence for how some infectious agents may manipulate these mechanisms. The protozoan Toxoplasma gondii, the causative agent of toxoplasmosis, is focused on as a prime example. Selective pressures appear to have allowed this parasite to evolve strategies to alter the behaviour in its natural intermediate rodent host. Latent infection has also been associated with a range of altered behavioural profiles, from subtle to severe, in other secondary host species including humans. In addition to enhancing our knowledge of the evolution of parasite manipulation in general, to further our understanding of how and when these potential changes to human host behaviour occur, and how we may prevent or manage them, it is imperative to elucidate the associated mechanisms involved.

Cytokines in schizophrenia: possible role of anti-inflammatory medications in clinical and preclinical stages

AIMS

In this paper, we review the literature on the efficacy of anti-inflammatory agents as neuroprotectors in clinical and preclinical stages of schizophrenia.

METHOD

A synthetic and integrative approach was applied to review studies stemming from epidemiology, phenomenology, cognition, genetics and neuroimaging data. We provide conclusions and future directions of research on early-onset schizophrenia.

RESULTS

Abnormal inflammatory activation has been demonstrated in schizophrenia. Increases or imbalances in cytokines before birth or during childhood may impact neurodevelopment and produce vulnerability to schizophrenia. The specificity of inflammatory abnormalities in psychiatric disorders is controversial. Similar increases in pro-inflammatory cytokines have been described in other disorders, especially mood and anxiety disorders. One of the most important challenges at this point is the understanding of neurobiological correlates of prodromal stages of schizophrenia.

CONCLUSION

Although future research should investigate the exact role of different cytokines in pathophysiology of schizophrenia, these mediators emerge as promising molecular targets to its prevention and treatment.

Anti-streptococcus IgM antibodies induce repetitive stereotyped movements: cell activation and co-localization with Fcα/μ receptors in the striatum and motor cortex

Group A beta-hemolytic streptococcus (GABHS) infections are implicated in neuropsychiatric disorders associated with an increased expression of repetitive stereotyped movements. Anti-streptococcus IgG presumably cross-reacts with elements on basal ganglia cells, modifies their function, and triggers symptoms. IgM may play a unique role in precipitating behavioral disturbances since variations in cortico-striatal activity occur in temporal congruity with peak IgM titers during an orchestrated immune response. We discovered in Balb/c mice that single subcutaneous injections of mouse monoclonal IgM antibodies to streptococcus group A bacteria induce marked dose-dependent increases in repetitive stereotyped movements, including head bobbing, sniffing, and intense grooming. Effects were antibody- and antigen-specific: anti-streptococcus IgG stimulated ambulatory activity and vertical activity but not these stereotypies, while anti-KLH IgM reduced activity. We suggest that anti-streptococcus IgM and IgG play unique roles in provoking GABHS-related behavioral disturbances. Paralleling its stereotypy-inducing effects, anti-streptococcus IgM stimulated Fos-like immunoreactivity in regions linked to cortico-striatal projections involved in motor control, including subregions of the caudate, nucleus accumbens, and motor cortex. This is the first evidence that anti-streptococcus IgM antibodies induce in vivo functional changes in these structures. Moreover, there was a striking similarity in the distributions of anti-streptococcus IgM deposits and Fos-like immunoreactivity in these regions. Of further importance, Fcα/μ receptors, which bind IgM, were present- and co-localized with anti-streptococcus IgM in these structures. We suggest that anti-streptococcus IgM-induced alterations of cell activity reflect local actions of IgM that involve Fcα/μ receptors. These findings support the use of anti-streptococcus monoclonal antibody administration in Balb/c mice to model GABHS-related behavioral disturbances and identify underlying mechanisms.

Central metabolite changes and activation of microglia after peripheral interleukin-2 challenge

Interleukin (IL)-2 regulates the immune response through the proliferation of activated T-cells and also exerts effects on the central nervous system (CNS). Alongside having marked neurobehavioral effects, IL-2 has been suggested to impact on various psychiatric disorders. The immune-CNS communication of IL-2 remains unclear, although, it is suggested that microglia are the source and target of IL-2. Here, we analyzed changes in brain metabolites following a peripheral IL-2 challenge and examined the contribution of microglia in mediating these effects. Rats were assessed by magnetic resonance spectroscopy (MRS) in a 9.4 T scanner for baseline metabolite levels in the prefrontal cortex (PFC) and the hippocampus. After 7 days animals were scanned again following a single injection of IL-2 (2.5 μg/kg) and then tested on the elevated plus-maze for the correlation of IL-2-induced brain metabolites and measures of anxiety. In another experiment CD25(+) microglia cells were determined. A separate group of rats was injected either with IL-2 or vehicle, and afterward the PFC and hippocampus were dissected and fluorescence activated cell sorting (FACS) analysis was performed. The MRS scans in the intra-individual study design showed a significant increase in myo-inositol in the analyzed regions. A significant correlation of anxiety-like measures and myo-inositol, a marker for microglia activity, was found in the hippocampus. The FACS analysis showed a significant increase in CD25(+) microglia in the hippocampus compared to controls. The results support the role of microglia as a mediator in the immune-CNS communication and the effects of peripheral IL-2.

Developmental vitamin D deficiency causes abnormal brain development

There is now clear evidence that vitamin D is involved in brain development. Our group is interested in environmental factors that shape brain development and how this may be relevant to neuropsychiatric diseases including schizophrenia. The origins of schizophrenia are considered developmental. We hypothesised that developmental vitamin D (DVD) deficiency may be the plausible neurobiological explanation for several important epidemiological correlates of schizophrenia namely: (1) the excess winter/spring birth rate, (2) increased incidence of the disease in 2nd generation Afro-Caribbean migrants and (3) increased urban birth rate. Moreover we have published two pieces of direct epidemiological support for this hypothesis in patients. In order to establish the "Biological Plausibility" of this hypothesis we have developed an animal model to study the effect of DVD deficiency on brain development. We do this by removing vitamin D from the diet of female rats prior to breeding. At birth we return all dams to a vitamin D containing diet. Using this procedure we impose a transient, gestational vitamin D deficiency, while maintaining normal calcium levels throughout. The brains of offspring from DVD-deficient dams are characterised by (1) a mild distortion in brain shape, (2) increased lateral ventricle volumes, (3) reduced differentiation and (4) diminished expression of neurotrophic factors. As adults, the alterations in ventricular volume persist and alterations in brain gene and protein expression emerge. Adult DVD-deficient rats also display behavioural sensitivity to agents that induce psychosis (the NMDA antagonist MK-801) and have impairments in attentional processing. In this review we summarise the literature addressing the function of vitamin D on neuronal and non-neuronal cells as well as in vivo results from DVD-deficient animals. Our conclusions from these data are that vitamin D is a plausible biological risk factor for neuropsychiatric disorders and that vitamin D acts as a neurosteroid with direct effects on brain development.

Spinal injection of IL-2 or IL-15 alters mechanical and thermal withdrawal thresholds in rats

IL-2 and IL-15 were tested for effects on responses to mechanical or thermal stimuli when spinally administered to male Sprague-Dawley rats with surgically implanted intrathecal catheters. Restricted doses of both IL-2 and IL-15 produced increased responsiveness to mechanical stimulation of the hindpaws. This effect lasted up to 48 h. IL-2 had biphasic effects on thermal responses whereas IL-15 produced thermal hypalgesia alone. These effects dissipated within 24h. These results suggest that IL-2 and IL-15 may participate in the generation of hyperalgesia in some pain conditions.

Cytokine levels during pregnancy influence immunological profiles and neurobehavioral patterns of the offspring

The underlying causes of autism spectrum disorders (ASD) are unknown, but clinical and experimental studies indicate immune mechanisms, in general, and cytokine dysregulation, in particular, as contributing factors in their etiology. We developed a prenatal mouse model of autism to demonstrate that circulating levels of defined cytokines in pregnant dams could influence fetal development and behavioral characteristics in their offspring. We administered daily injections of murine IL-2 (0.4 mug in phosphate-buffered saline [PBS]) to pregnant mice during mid-gestation, and analyzed their offspring (IL-2 pups) in comparison to offspring of pregnant mice injected with vehicle only (PBS pups). Significant levels of IL-2 were present in amniotic fluid and tissues from embryos of dams given radiolabeled IL-2, indicating that the injected IL-2 crossed the placenta and entered the fetuses. Lymphocytes from IL-2 pups demonstrated accelerated T cell development, with a skewing toward TH1 cell differentiation. IL-2 pups also showed in vitro proliferative and cytotoxicity responses that were significantly higher than control PBS pups when stimulated with syngeneic B lymphoma cells or allogeneic spleen cells. In addition to their previously shown increases in open-field activity, grooming and rearing behavior, offspring of IL-2-injected (vs. PBS-injected) dams also displayed abnormal new motor learning as assessed through acquisition of the classically conditioned eyeblink response. These results suggest that increases in maternal levels of IL-2 during pregnancy induce in their offspring long-lasting increased vulnerability to neurobehavioral abnormalities associated with autism, and provide a valid animal model to determine the underlying immunological mechanisms.

Psychoimmunological effects of dioscorea in ovariectomized rats: role of anxiety level

BACKGROUND

Anxiety levels in rats are correlated with interleukin-2 (IL-2) levels in the brain. The aim of the present study was to investigate the effects of dioscorea (wild yam), a Chinese medicine, on emotional behavior and IL-2 levels in the brain of ovariectomized (OVX) rats.

METHODS

One month after ovariectomy, female Wistar rats were screened in the elevated plus-maze (EPM) test to measure anxiety levels and divided into low anxiety (LA) and high anxiety (HA) groups, which were then given dioscorea (250, 750, or 1500 mg/kg/day) by oral gavage for 27 days and were tested in the EPM on day 23 of administration and in the forced swim test (FST) on days 24 and 25, then 3 days later, the brain was removed and IL-2 levels measured.

RESULTS

Compared to sham-operated rats, anxiety behavior in the EPM was increased in half of the OVX rats. After chronic dioscorea treatment, a decrease in anxiety and IL-2 levels was observed in the HA OVX rats. Despair behavior in the FST was inhibited by the highest dosage of dioscorea.

CONCLUSION

These results show that OVX-induced anxiety and changes in neuroimmunological function in the cortex are reversed by dioscorea treatment. Furthermore, individual differences need to be taken into account when psychoneuroimmunological issues are measured and the EPM is a useful tool for determining anxiety levels when examining anxiety-related issues.

Effects of toxoplasma on human behavior

Although latent infection with Toxoplasma gondii is among the most prevalent of human infections, it has been generally assumed that, except for congenital transmission, it is asymptomatic. The demonstration that latent Toxoplasma infections can alter behavior in rodents has led to a reconsideration of this assumption. When infected human adults were compared with uninfected adults on personality questionnaires or on a panel of behavioral tests, several differences were found. Other studies have demonstrated reduced psychomotor performance in affected individuals. Possible mechanisms by which T. gondii may affect human behavior include its effect on dopamine and on testosterone.

Poorer results of mice with latent toxoplasmosis in learning tests: impaired learning processes or the novelty discrimination mechanism?

The heteroxenous protozoan parasite Toxoplasma gondii is transmitted from the intermediate host (any warm-blooded animal) to the definitive host (members of the felidae) by carnivory. The infected intermediate hosts develop several specific behavioural changes that are usually considered products of manipulative activity of the parasite aimed to increase the probability of its transmission to the definitive host. Among other changes, the infected rodents were shown to have impaired learning capability. All previous studies were done 2–6 weeks after the infection. Therefore, it was difficult to resolve whether the observed impairment of learning processes was a result of acute or latent toxoplasmosis, i.e. whether it was a side-effect of the disease or a product of manipulation activity. Here we studied the learning capability of Toxoplasma-infected mice in the static rod test and 8-arm radial maze test and their spontaneous activity in the wheel running test 10 weeks after the infection. The infected mice achieved worse scores in the learning tests but showed higher spontaneous activity in the wheel running test. However, a detailed study of the obtained results as well as of the data reported by other authors suggested that the differences between infected and control mice were a result of impaired ability to recognize novel stimuli rather than of impaired learning capacity in animals with latent toxoplasmosis.

Involvement of neuropeptide systems in schizophrenia: human studies

Neuropeptides are heterogeneously distributed throughout the digestive, circulatory, and nervous systems and serve as neurotransmitters, neuromodulators, and hormones. Neuropeptides are phylogenetically conserved and have been demonstrated to regulate numerous behaviors. They have been hypothesized to be pathologically involved in several psychiatric disorders, including schizophrenia. On the basis of preclinical data, numerous studies have sought to examine the role of neuropeptide systems in schizophrenia. This chapter reviews the clinical data, linking alterations in neuropeptide systems to the etiology, pathophysiology, and treatment of schizophrenia. Data for the following neuropeptide systems are included: arginine-vasopressin, cholecystokinin (CCK), corticotropin-releasing factor (CRF), interleukins, neuregulin 1 (NRG1), neurotensin (NT), neuropeptide Y (NPY), opioids, secretin, somatostatin, tachykinins, thyrotropin-releasing hormone (TRH), and vasoactive intestinal peptide (VIP). Data from cerebrospinal fluid (CSF), postmortem and genetic studies, as well as clinical trials are described. Despite the inherent difficulties associated with human studies (including small sample size, variable duration of illness, medication status, the presence of comorbid psychiatric disorders, and diagnostic heterogeneity), several findings are noteworthy. Postmortem studies support disease-related alterations in several neuropeptide systems in the frontal and temporal cortices. The strongest genetic evidence supporting a role for neuropeptides in schizophrenia are those studies linking polymorphisms in NRG1 and the CCKA receptor with schizophrenia. Finally, the only compounds that act directly on neuropeptide systems that have demonstrated therapeutic efficacy in schizophrenia are neurokinin receptor antagonists. Clearly, additional investigation into the role of neuropeptide systems in the etiology, pathophysiology, and treatment of schizophrenia is warranted.

Cytokines in schizophrenia and the effects of antipsychotic drugs

Growing evidence suggests that the immune, endocrine, and nervous systems interact with each other through cytokines, hormones, and neurotransmitters. The activation of the cytokine systems may be involved in the neuropathological changes occurring in the central nervous system (CNS) of schizophrenic patients. Numerous studies report that treatment with antipsychotic drugs affects the cytokine network. Hence, it is plausible that the influence of antipsychotics on the cytokine systems may be responsible for their clinical efficacy in schizophrenia. This article reviews current data on the cytokine-modulating potential of antipsychotic drugs. First, basic information on the cytokine networks with special reference to their role in the CNS as well as an up-to-date knowledge of the cytokine alterations in schizophrenia is outlined. Second, the hitherto published studies on the influence of antipsychotics on the cytokine system are reviewed. Third, the possible mechanisms underlying antipsychotics' potential to influence the cytokine networks and the most relevant aspects of this activity are discussed. Finally, limitations of the presented studies and prospects of future research are delineated.

Effects of cytokines and infections on brain neurochemistry

Administration of cytokines to animals can elicit many effects on the brain, particularly neuroendocrine and behavioral effects. Cytokine administration also alters neurotransmission, which may underlie these effects. The most well studied effect is the activation of the hypothalamo-pituitary-adrenocortical (HPA) axis, especially that by interleukin-1 (IL-1). Peripheral and central administration of IL-1 also induces norepinephrine (NE) release in the brain, most markedly in the hypothalamus. Small changes in brain dopamine (DA) are occasionally observed, but these effects are not regionally selective. IL-1 also increases brain concentrations of tryptophan, and the metabolism of serotonin (5-HT) throughout the brain in a regionally nonselective manner. Increases of tryptophan and 5-HT, but not NE, are also elicited by IL-6, which also activates the HPA axis, although it is much less potent in these respects than IL-1. IL-2 has modest effects on DA, NE and 5-HT. Like IL-6, tumor necrosis factor-α (TNFα) activates the HPA axis, but affects NE and tryptophan only at high doses. The interferons (IFN's) induce fever and HPA axis activation in man, but such effects are weak or absent in rodents. The reported effects of IFN's on brain catecholamines and serotonin have been very varied. However, interferon-γ, and to a lesser extent, interferon-α, have profound effects on the catabolism of tryptophan, effectively reducing its concentration in plasma, and may thus limit brain 5-HT synthesis.Administration of endotoxin (LPS) elicits responses similar to those of IL-1. Bacterial and viral infections induce HPA activation, and also increase brain NE and 5-HT metabolism and brain tryptophan. Typically, there is also behavioral depression. These effects are strikingly similar to those of IL-1, suggesting that IL-1 secretion, which accompanies many infections, may mediate these responses. Studies with IL-1 antagonists, support this possibility, although in most cases the antagonism is incomplete, suggesting the existence of multiple mechanisms. Because LPS is known to stimulate the secretion of IL-1, IL-6 and TNFα, it seems likely that these cytokines mediate at least some of the responses, but studies with antagonists indicate that there are multiple mechanisms. The neurochemical responses to cytokines are likely to underlie the endocrine and behavioral responses. The NE response to IL-1 appears to be instrumental in the HPA activation, but other mechanisms exist. Neither the noradrenergic nor the serotonergic systems appear to be involved in the major behavioral responses. The significance of the serotonin response is unknown.

Monoamine and motor responses to cocaine are co-deficient in the Fawn-Hooded depressed animal model

The Fawn-Hooded (FH) genetic animal model of depression continues to be of interest because the FH model has limited biochemical and immune function. The FH animal has an inherited trait, platelet storage pool deficiency (PSPD), an hemorrhagic disorder that is also a component of Chediak-Higashi syndrome (CHS). CHS is a pyrogenic infectious childhood disease; few patients live past the age of 20. Our hypothesis was that FH animals may exhibit different monoamine and motor responses to cocaine versus the Sprague-Dawley (SD) "normal" animal strain, which does not have the FH trait. Therefore, selective neuromolecular imaging (NMI) of the monoamines, dopamine (DA) and 5-HT within nucleus accumbens (NAcc) of behaving male FH versus SD rats was performed in vivo with BRODERICK PROBE sensors and a semiderivative voltammetric circuit. Each animal was placed in a faraday chamber and electrochemical signals were detected via a mercury commutator and flexible cable. Baseline values for neurotransmitters and behavior were derived during the last half-hour of habituation behavior. Release of DA and 5-HT was detected selectively, at separate oxidation potentials, within seconds, before and after intraperitoneal administration of the psychostimulant, cocaine (10 mg/kg). At the same time, frequencies of ambulations and central ambulations were separately monitored with infrared photobeams, which surrounded the faraday chamber. Data were compared by ANOVA analysis followed by Tukey's post hoc test. The data showed that (1) DA release in NAcc of behaving FH animals did not respond to cocaine; neither first hour nor second hour values significantly differed from baseline (both hours, p>0.05), whereas SD animals exhibited a significant increase in cocaine-induced DA release in NAcc (both hours, p<0.001). The ability for acute cocaine to increase DA release in NAcc was significantly greater in SD than in FH animals (p<0.001). (2) 5-HT release in NAcc of behaving FH animals was not significantly increased by cocaine (both hours, p>0.05), whereas 5-HT release in NAcc of SD animals was significantly increased after cocaine (both hours, p<0.001). The ability for acute cocaine to increase 5-HT release was significantly greater in SD than in FH animals (p<0.001). (3) Ambulations in the FH strain were modestly, yet significantly, enhanced after cocaine during both hours of study (p<0.05, p<0.001, respectively) as were ambulations in the SD strain. Nonetheless, the ability for acute cocaine to increase ambulations was significantly greater in SD than in FH animals in the first hour (p<0.001). (4) Central ambulations in the FH strain was not affected by cocaine (both hours, p>0.05), whereas SD animals showed a significant increase in central ambulatory activity in both hours of the cocaine study (p<0.001). The ability for acute cocaine to increase central ambulations was significantly greater in SD than in FH animals (p<0.001). Thus, this is the first study to determine in vivo the neurochemical response to acute cocaine in the behaving FH animal. Moreover, this is the first study to determine in vivo and simultaneously the neurochemical and behavioral response to acute cocaine in the FH strain in comparison with SD animals, a "normal" strain. Remarkable deficiencies in the ability for acute cocaine to alter neurochemistry and behavior in animals with the FH trait are shown. These studies emphasize the need to look differentially at cocaine effects in biochemically and immune-compromised subjects versus "normal" subjects.

Striatal microinjections of interleukin-2 and rat behaviour in the elevated plus-maze

We showed that the relationship between cytokine mRNA in the rat brain and elevated plus-maze behaviour is site- (striatum, prefrontal cortex), and cytokine-specific (interleukin-2). Here, we investigated whether a striatal microinjection of interleukin-2 (1, 10, 25 ng) affects elevated plus-maze behaviour. Analyses showed no acute effects of IL-2 on open arm time, whereas dose-dependent differences in rearing activity, and open arm entries became apparent between IL-2 doses. Twenty-four hours later, a previous dose of 25 ng IL-2 showed a trend for more open arm time compared to vehicle. These behavioural changes are discussed in relation to anxiety-relevant and exploratory behaviour, and possible neurochemical mechanisms.

Cytokine modulation of defensive rage behavior in the cat: role of GABAA and interleukin-2 receptors in the medial hypothalamus

Defensive rage behavior is a form of aggressive behavior occurring in nature in response to a threatening stimulus. It is also elicited by stimulation of the medial hypothalamus and midbrain periaqueductal gray (PAG) and mediated through specific neurotransmitter-receptor mechanisms within these regions. Since interleukin (IL)-2 modulates the release of neurotransmitters linked to aggression and rage, we sought to determine whether IL-2 microinjected into the medial hypothalamus would modulate defensive rage. Microinjections of relatively low doses of IL-2 into the medial hypothalamus significantly suppressed defensive rage elicited from the PAG in a dose-dependent manner and in the absence of signs of sickness behavior. Pre-treatment with an antibody directed against IL-2Ralpha or a GABA(A) receptor antagonist blocked IL-2's suppressive effects upon defensive rage. Since the suppression of defensive rage is also mediated by 5-HT(1) receptors in the medial hypothalamus, a 5-HT(1) antagonist was microinjected into this region as a pretreatment for IL-2; however, it did not block IL-2's suppressive effects. Immunocytochemical data provided anatomical support for these findings by revealing extensive labeling of IL-2Ralpha on neurons in the medial hypothalamus. IL-2 microinjected into the medial hypothalamus did not modulate predatory attack elicited from the lateral hypothalamus. In summary, we provide evidence for a novel role for IL-2 in the medial hypothalamus as a potent suppressor of defensive rage behavior. These effects are mediated through an IL-2-GABA(A) receptor mechanism.

Probable neuroimmunological link between Toxoplasma and cytomegalovirus infections and personality changes in the human host

Background

Recently, a negative association between Toxoplasma-infection and novelty seeking was reported. The authors suggested that changes of personality trait were caused by manipulation activity of the parasite, aimed at increasing the probability of transmission of the parasite from an intermediate to a definitive host. They also suggested that low novelty seeking indicated an increased level of the neurotransmitter dopamine in the brain of infected subjects, a phenomenon already observed in experimentally infected rodents. However, the changes in personality can also be just a byproduct of any neurotropic infection. Moreover, the association between a personality trait and the toxoplasmosis can even be caused by an independent correlation of both the probability of Toxoplasma-infection and the personality trait with the third factor, namely with the size of living place of a subject. To test these two alternative hypotheses, we studied the influence of another neurotropic pathogen, the cytomegalovirus, on the personality of infected subjects, and reanalyzed the original data after the effect of the potential confounder, the size of living place, was controlled.

Methods

In the case-control study, 533 conscripts were tested for toxoplasmosis and presence of anti-cytomegalovirus antibodies and their novelty seeking was examined with Cloninger's TCI questionnaire. Possible association between the two infections and TCI dimensions was analyzed.

Results

The decrease of novelty seeking is associated also with cytomegalovirus infection. After the size of living place was controlled, the effect of toxoplasmosis on novelty seeking increased. Significant difference in novelty seeking was observed only in the largest city, Prague.

Conclusion

Toxoplasma and cytomegalovirus probably induce a decrease of novelty seeking. As the cytomegalovirus spreads in population by direct contact (not by predation as with Toxoplasma), the observed changes are the byproduct of brain infections rather than the result of manipulation activity of a parasite. Four independent lines of indirect evidence, namely direct measurement of neurotransmitter concentration in mice, the nature of behavioral changes in rodents, the nature of personality changes in humans, and the observed association between schizophrenia and toxoplasmosis, suggest that the changes of dopamine concentration in brain could play a role in behavioral changes of infected hosts.

Kainate-activated currents in the ventral tegmental area of neonatal rats are modulated by interleukin-2

Interleukin (IL)-2 is a potent modulator of neurotransmission and neuronal development in the mesolimbic and mesostriatal systems. It is also implicated in pathologies (including schizophrenia, Parkinson's disease, autism, cognitive disorders) that are linked with abnormalities in these systems. Since the kainate receptor plays an essential role in mesolimbic neuronal development and excitability, we examined the effects of physiologically relevant concentrations of IL-2 on kainate-activated current (I(KA)) in voltage-clamped neurons freshly isolated from the ventral tegmental area (VTA) of 3- to 14-day-old rats. IL-2 (0.01-10 ng/ml) alone had no effect on membrane conductance. When co-applied with kainate, IL-2 significantly decreased I(KA). IL-2 (2 ng/ml) shifted the kainate concentration-response curve to the right in a parallel manner, significantly increasing the EC(50) without changing the maximal I(KA). IL-2 inhibition of I(KA) was voltage-dependent, being greater at negative potentials. IL-2 did not alter the reversal potential. These findings suggest that IL-2 potently modulates kainate receptors of developing mesolimbic neurons. We suggest that IL-2 plays a role in the excitability of developing neurons in the mesolimbic system. Inasmuch as increased I(KA) is associated with excitotoxicity, coupled with the present observation that IL-2 inhibits I(KA), we suggest an adaptive role for IL-2 in limiting excitotoxicity in the developing brain. IL-2 might thus be required for normal cell development in the mesolimbic and mesostriatal systems.

Cytokines, stressors, and clinical depression: augmented adaptation responses underlie depression pathogenesis

By influencing the central nervous system, cytokines, which regulate immune function innately and adaptively, may play a key role in mediating depression-like neuro-behavioral changes. However, the similarity between cytokine and stressor-effects in animal models raises a question about the degree to which behavioral and neurochemical outcomes of cytokine challenge represent depressive disorder per se. The present review attempts to illustrate the degree of overlap between cytokines and stressors with respect to their effects on neurochemistry and behavior in animal models. The review also shows how short-term effects of cytokine exposure in typical animals may be discerned from characteristics that might otherwise be described as depression-like. By comparing outcomes of immune challenge in typical rodent strains (e.g., Sprague-Dawley [SD], Wistar) and an accepted animal model of depression (e.g., Fawn Hooded [FH] rodent strain), differences between short-term effects of cytokines and depression-like characteristics in rodents are demonstrated. Additionally, because it is known that preexisting vulnerability to depression may affect outcomes of immune challenge, we further compare immunological, biochemical and behavioral effects of cytokines between SD and FH rodent strains. Interestingly, the acute neurochemical and behavioral effects of the cytokine interleukin 1alpha (IL-1alpha) reveal stressor-like responses during behavioral habituation in both strains, though this appears to a stronger degree in FH animals. Further, the subacute response to IL-1alpha vastly differed between strains, indicating differences in adaptive mechanisms. Thus, stressor-like effects of immune challenge, particularly in FH animals, provide validation for recent "cross-sensitization" models of depression pathogenesis that incorporate immune factors.

Cytokine mRNA levels in brain and peripheral tissues of the rat: relationships with plus-maze behavior

There is evidence that interleukin (IL)-2 may be related to anxiety as measured in the elevated plus-maze. Recently, we showed that normal adult male Wistar rats can differ systematically in this test of avoidance behavior, that is, time spent on the open arms of the elevated plus-maze. Rats with low open arm time had higher striatal levels of IL-2 mRNA than those with high open arm time, but did not differ significantly in expression of other striatal cytokine mRNA. Here, we investigated whether these expression effects are anatomically specific to the striatum. Therefore, we asked in this double-blind study whether elevated plus-maze behavior may also be related to endogenous levels of cytokine mRNA in other brain regions, which play a role for anxiety, namely the amygdala, hippocampus, and the prefrontal cortex. Additionally, and as peripheral controls, immuno-neuro-endocrine relevant tissues (adrenal glands, spleen) were analyzed. Based on open arm time in the elevated plus-maze, male Wistar rats were divided into sub-groups with either low or high open arm time behavior. Then, IL-1beta, IL-2, IL-6, and tumor necrosis factor (TNF)-alpha cDNA levels were measured post-mortem using semi-quantitative, competitive, reverse transcription polymerase chain reaction. First, we found that cytokine expressions differed considerably between and within these central and peripheral tissues. Secondly, rats with high compared to low open arm time behavior showed higher IL-2 mRNA levels in the prefrontal cortex, which is an inverse pattern to what we recently found in the striatum. These results provide new evidence indicating that cytokine mRNA in the brain can be related to elevated plus-maze behavior and that this relationship is site (prefrontal cortex, striatum)- and cytokine mRNA-specific (IL-2).

Behavioral and neurochemical responses in mice bearing tumors submitted to social stress

Through the proinflammatory cytokines secreted in response to inflammation or injury, the immune system produces physiological and behavioral alterations. This study analyzes the effects on behavior, mononuclear proliferative response and central monoamine activity in response to the inoculation of tumor cells in mice submitted to social stress. Two groups of male OF1 mice were used, one of which was inoculated with B16 melanoma cells. Both groups were subdivided into two new groups, with one being submitted to social stress through sensory contact model with a selected aggressive subject, and the other being handled without social interaction. Subjects were exposed to social stress for a 24-h period, with three 5 min intervals of direct physical interaction, where the behavior was recorded and assessed. One hour after the stress and/or handling, they were put down and samples taken for physiological assessment. Significant behavioral changes were found in subjects with implanted tumors, mainly characterized by an increase in avoidance behavior and a decrease in immobility, defense-submission and non-social exploration behavior, coupled with an increase in the spleen mononuclear cell proliferative response. Similarly, an increase was observed in the density of dopamine(2) (D(2))-receptors in the striatum (SRT) and an increase in dopaminergic (DOPAC/DA) and serotonergic (5HIAA/5HT) turnover in the hypothalamus. The increase in the density of D(2)-receptors in the SRT coincides with the decrease in some behaviors with a predominant motor component. The results indicate significant changes in the defensive strategy used to cope with situations of intense social stress in mice bearing tumors.