Human interferon-alpha induces immobility in the mouse forced swimming test: involvement of the opioid system

A new insight into mechanisms of interferon alpha neurotoxicity: Expression of GRIN3A subunit of NMDA receptors and NMDA-evoked exocytosis

Neurological and psychiatric side effects accompany the high-dose interferon-alpha (IFNA) therapy. The primary genes responsible for these complications are mostly unknown. Our genome-wide search in mouse and rat genomes for the conservative genes containing IFN-stimulated response elements (ISRE) in their promoters revealed a new potential target gene of IFNA, Grin3α, which encodes the 3A subunit of NMDA receptor. This study aimed to explore the impact of IFNA on the expression of Grin3α and Ifnα genes and neurotransmitters endo/exocytosis in the mouse brain. We administered recombinant human IFN-alpha 2b (rhIFN-α2b) intracranially, and 24 h later, we isolated six brain regions and used the samples for RT-qPCR and western blot analysis. Synaptosomes were isolated from the cortex to analyze endo/exocytosis with acridine orange and L-[14C]glutamate. IFNA induced an increase in Grin3α mRNA and GRIN3A protein, but a decrease in Ifnα mRNA and protein. IFNA did not affect the accumulation and distribution of L-[14C]glutamate and acridine orange between synaptosomes and the extra-synaptosomal space. It caused the more significant acridine orange release activated by NMDA or glutamate than from control mice's synaptosomes. In response to IFNA, the newly discovered association between elevated Grin3α expression and NMDA- and glutamate-evoked neurotransmitters release from synaptosomes implies a new molecular mechanism of IFNA neurotoxicity.

Imaging the Role of Inflammation in Mood and Anxiety-related Disorders

Background

Studies investigating the impact of a variety of inflammatory stimuli on the brain and behavior have reported evidence that inflammation and release of inflammatory cytokines affect circuitry relevant to both reward and threat sensitivity to contribute to behavioral change. Of relevance to mood and anxiety-related disorders, biomarkers of inflammation such as inflammatory cytokines and acute-phase proteins are reliably elevated in a significant proportion of patients with major depressive disorder (MDD), bipolar disorder, anxiety disorders and post-traumatic stress disorder (PTSD).

Methods

This review summarized clinical and translational work demonstrating the impact of peripheral inflammation on brain regions and neurotransmitter systems relevant to both reward and threat sensitivity, with a focus on neuroimaging studies involving administration of inflammatory stimuli. Recent translation of these findings to further understand the role of inflammation in mood and anxiety-related disorders is also discussed.

Results

Inflammation was consistently found to affect basal ganglia and cortical reward and motor circuits to drive reduced motivation and motor activity, as well as anxiety-related brain regions including amygdala, insula and anterior cingulate cortex, which may result from cytokine effects on monoamines and glutamate. Similar relationships between inflammation and altered neurocircuitry have been observed in MDD patients with increased peripheral inflammatory markers, and such work is on the horizon for anxiety disorders and PTSD.

Conclusion

Neuroimaging effects of inflammation on reward and threat circuitry may be used as biomarkers of inflammation for future development of novel therapeutic strategies to better treat mood and anxiety-related disorders in patients with high inflammation.

Beneficial effect of aspirin against interferon-α-2b-induced depressive behavior in Sprague Dawley rats

Accumulating data advocates that inflammatory mediators may contribute to depression in experimental models as well as in humans. Nonetheless, whether anti-inflammatory treatments can prevent depression still remains controversial. To substantiate our hypothesis, we used an interferon-α-2b model of depression using Sprague Dawley rats. Interferon-α-2b is a cytokine which activates immune response and also produces depression. The animals were treated for 21 days with aspirin (10 mg/kg, per oral (p.o.)) dexamethasone (1 mg/kg p.o.) and amitriptyline (10 mg/kg p.o.). Amitriptyline was used as reference standard, and given concurrently with aspirin and dexamethasone to examine any synergy. Interferon-α-2b (6000 IU/kg, intraperitoneal (i.p.)) was administered in all the above groups daily, except normal control. Tests performed included sucrose preference test, behavioural tests like forced swim test, elevated plus maze, light dark box and locomotor activity along with biochemical estimations like serum cortisol and brain neurotransmitters. The rats in the group treated with Interferon-α-2b produced depressive behaviour in rats. We found that animals treated with aspirin decreased immobility time in forced swim test, increased sucrose preference, decreased serum cortisol and increased brain serotonin levels signifying antidepressant action. In contrast, there was no effect in groups treated with dexamethasone. Our results suggest that aspirin can serve as a potential antidepressant both individually and as adjuvant agent in the treatment of depression. Inhibition of the cyclo-oxygenase-2 levels and prostaglandins concentration or any other potential physiological and biochemical mechanisms may be involved in antidepressant effect.

Inflammation Effects on Motivation and Motor Activity: Role of Dopamine

Motivational and motor deficits are common in patients with depression and other psychiatric disorders, and are related to symptoms of anhedonia and motor retardation. These deficits in motivation and motor function are associated with alterations in corticostriatal neurocircuitry, which may reflect abnormalities in mesolimbic and mesostriatal dopamine (DA). One pathophysiologic pathway that may drive changes in DAergic corticostriatal circuitry is inflammation. Biomarkers of inflammation such as inflammatory cytokines and acute-phase proteins are reliably elevated in a significant proportion of psychiatric patients. A variety of inflammatory stimuli have been found to preferentially target basal ganglia function to lead to impaired motivation and motor activity. Findings have included inflammation-associated reductions in ventral striatal neural responses to reward anticipation, decreased DA and DA metabolites in cerebrospinal fluid, and decreased availability, and release of striatal DA, all of which correlated with symptoms of reduced motivation and/or motor retardation. Importantly, inflammation-associated symptoms are often difficult to treat, and evidence suggests that inflammation may decrease DA synthesis and availability, thus circumventing the efficacy of standard pharmacotherapies. This review will highlight the impact of administration of inflammatory stimuli on the brain in relation to motivation and motor function. Recent data demonstrating similar relationships between increased inflammation and altered DAergic corticostriatal circuitry and behavior in patients with major depressive disorder will also be presented. Finally, we will discuss the mechanisms by which inflammation affects DA neurotransmission and relevance to novel therapeutic strategies to treat reduced motivation and motor symptoms in patients with high inflammation.

Role of Inflammation in the Development of Neuropsychiatric Symptom Domains: Evidence and Mechanisms

The finding that inflammatory markers are elevated in various neuropsychiatric disorders raises the need of identifying the precise research domain criteria driven by inflammation. Based on the model of inflammation-induced depression it has been possible to identify distinct pathophysiological pathways leading to alterations in neurotransmitter metabolism with specific relevance for the development of symptom constellations that are common to various neuropsychiatric and neurodegenerative conditions. Moreover, converging data indicate that these pathways interact with relevant vulnerability factors and modulatory systems to ultimately impact the presentation of inflammation-driven neuropsychiatric symptoms. Altogether, these findings make inflammation a key pivotal factor in psychopathology. Developing treatments that target inflammation and modulate the pathways and systems by which inflammatory processes selectively affect brain function will be of particular relevance for the treatment of specific neurobehavioral symptom domains.

Interferon-α induces neurotoxicity through activation of the type I receptor and the GluN2A subunit of the NMDA receptor

Elevated levels of interferon-alpha (IFNα) in the central nervous system (CNS) are linked to cognitive dysfunction in patients with inflammatory CNS diseases such as HIV-associated neurocognitive disorders (HAND). Increased CNS IFNα has also been found to be associated with cognitive dysfunction in a HAND mouse model. Here, we corroborate previous studies showing a dose-dependent decrease in dendritic branching and length caused by IFNα treatment and extend those studies. Because both direct and indirect mechanisms of IFNα-induced neurotoxicity are likely involved, the cell signaling pathway involving the IFNα receptor (IFNAR) was initially evaluated. Rat neuronal cultures exposed to IFNα demonstrate increased phosphorylation of STAT1 and increased interferon stimulating gene 15 (ISG15) expression, indicators of IFNAR engagement. However, specific blocking antibodies to the IFNAR were found to only partially protect neurons from IFNα-induced neurotoxicity. Additionally, inhibiting the GluN2A subunit of N-methyl-D-asparate receptor (NMDAR) was also found to be partially protective against IFNα-induced neurotoxicity compared with the GluN2B subunit. Neurotoxicity is evident in neurons extracted from IFNAR KO mice treated with IFNα as well, further indicating that IFNAR signaling is not required for IFNα neurotoxicity. The neurotoxic actions of IFNα are mediated through both the IFNAR as well as the GluN2A subunit of the NMDAR to reduce dendritic arborization in neurons. Complete protection from IFNα-induced neurotoxicity was demonstrated when both pathways were blocked. Blocking these pathways could lead to potential therapies for cognitive dysfunction during neuroinflammation and specifically lead to better treatments for HAND.

A starring role for microglia in brain sex differences

Microglia, the resident innate immune cells in the brain, have long been understood to be crucial to maintenance in the nervous system, by clearing debris, monitoring for infiltration of infectious agents, and mediating the brain's inflammatory and repair response to traumatic injury, stroke, or neurodegeneration. A wave of new research has shown that microglia are also active players in many basic processes in the healthy brain, including cell proliferation, synaptic connectivity, and physiology. Microglia, both in their capacity as phagocytic cells and via secretion of many neuroactive molecules, including cytokines and growth factors, play a central role in early brain development, including sexual differentiation of the brain. In this review, we present the vast roles microglia play in normal brain development and how perturbations in the normal neuroimmune environment during development may contribute to the etiology of brain-based disorders. There are notable differences between microglia and neuroimmune signaling in the male and female brain throughout the life span, and these differences may contribute to the vast differences in the incidence of neuropsychiatric and neurological disorders between males and females.

Central administration of murine interferon-α induces depressive-like behavioral, brain cytokine and neurochemical alterations in mice: a mini-review and original experiments

A role for pro-inflammatory cytokines and their neuroinflammatory signaling cascades in depressive pathology has increasingly gained acceptance. In this regard, several lines of evidence suggested that interleukin-1β (IL-1β) and tumor necrosis factor-α (TNF-α) can provoke neurochemical and hormonal changes akin to those associated with psychological stressors, and that these cytokines also induce sickness behaviors that resemble some of the neurovegetative features of depression. Similarly, human depressed patients often display marked changes of pro-inflammatory cytokine levels and immune cell activity. Perhaps more germane in the analysis of the cytokine-depression connection, reports of humans undergoing interferon-α (IFN-α) treatment for certain cancers or viral infections have indicated that the pro-inflammatory cytokine caused signs of major depression in a substantial subset of those treated. In the present investigation, we demonstrated that acute or repeated infusion of IFN-α into the lateral ventricles provoked depressive-like behavior and concomitant changes in serotonin (5-HT) and mRNA expression of particular 5-HT receptors and pro-inflammatory cytokines. These actions were less evident following administration directly into the prefrontal cortex and not apparent at all when administered to the dorsal raphe nucleus. The data are discussed in relation to the induction of depression elicited by IFN-α, and are presented in the context of a mini-review that highlights potential mechanisms through which the cytokine might act to promote psychomotor and affective disturbances and interact with stressors.

5-HT(1A) receptor and apoptosis contribute to interferon-α-induced "depressive-like" behavior in mice

Interferon-α (IFN-α)-induced "depressive-like" behavior is a major limitation for the treatment of hepatitis C virus (HCV), especially for patients with psychiatric disorders. Recently, serotonin 1A (5-HT(1A)) receptor and cellular apoptosis are involved in mechanism(s) contributing to depression. To gain insight into this mechanism(s), we used C57BL/6J mice to examine the impact of IFN-α on the modulation of 5-HT(1A) receptor and cellular apoptosis and their relationship. Our results showed that repeated administration of IFN-α (6 MIU/kg, s.c.) induced "depressive-like" behavior of mice in the forced swim test, tail suspension test and sucrose preference test. Besides, the depressive mice exhibited a notable downregulation of 5-HT(1A) receptor and upregulation of cleaved caspase-3 and Bax/Bcl-2 ratio. These changes could be blocked by the 5-HT(1A) receptor agonist 8-OH-DPAT (0.5 mg/kg, i.p., 30 min before IFN-α administration), but not by the standard antidepressant imipramine (10 mg/kg, i.p., 30 min before IFN-α administration) although both of them could ameliorate the depressive-like behavior of mice. These findings indicated that repeated injection with IFN-α provoked "depressive-like" behavior through cellular apoptosis, which could be ameliorated by the activation of 5-HT(1A) receptor.

Pegylated human interferon alpha 2a does not induce depression-associated changes in mice

Interferon (IFN) alpha proteins are proinflammatory cytokines having immunomodulating and antiviral properties. States during which cytokine systems are activated (e.g., during viral infection or during treatment of chronic hepatitis C and various malignancies with IFN alpha, etc.) can be associated with depression-like syndromes or even full-blown depressive episodes. Therefore, the role of IFN alpha and other cytokines in the pathogenesis of depressive disorder ("cytokine hypothesis of depression") has been assessed for many years with contradictory results. We have investigated whether intraperitoneal administration of high doses (up to 600 µg/kg body weight) of pegylated, recombinant human IFN alpha 2a in mice induces changes known to be associated with depression using three different readouts: behavior in a model of despair (Porsolt swim test), presence of anhedonia (sucrose preference test), and sensitivity of the hypothalamic-pituitary-adrenal system (dexamethasone suppression test). We also assessed potential IFN-induced changes in gene expression in the liver. In none of the performed experiments, depression-associated effects could be found despite very high serum levels of IFN-induced antiviral activity compared to levels measured in hepatitis C virus (HCV) patients treated routinely with pegylated recombinant human IFN alpha 2a. The lack of such expected effects is probably due to the fact that pegylated human recombinant IFN alpha 2a does not activate the murine class I IFN receptor. Our results do not support the hypothesis that administration of recombinant pegylated human IFN alpha to mice produces a robust model of depression.

Le kétoconazole antagonise les effets immuno-gonadotropes au test de la nage forcée chez le rat mâle Wistar

On a souvent rapporté que la dépression s’installe suite à des perturbations des activités de l’axe corticotrope et du système immunitaire. L’objectif de cette étude était d’explorer les effets du kétoconazole, un dérivé d’imidazole, inhibiteur de la stéroïdogénèse gonadique et surrénalienne, sur les variations du nombre de leucocytes totaux et des pourcentages de sous-populations leucocytaires, au cours de la nage forcée chez le rat (test de Porsolt), un test consiste à tester l’efficacité des antidépresseurs. Des cathéters ont été implantés, sous anesthésie générale, dans la carotide droite, et des prises de sang (0,2 mL) ont été réalisées à des intervalles de 15 min au cours de l’expérimentation, alors que les animaux pouvaient se comporter librement. Les degrés d’anxiété et d’activité locomotrice des rats ont été mesurés au labyrinthe en croix surélevée et au test des champs ouverts. La nage forcée a provoqué des fluctuations du système immunitaire et de la testostéronémie, lesquelles qui ont été inhibées suite au traitement des animaux au kétoconazole. Cet effet a été obtenu également sur le plan comportemental (labyrinthe en croix surélevée, nage forcée) dans le sens d’une amélioration (effets anxiolytique et antidépresseur). Ces résultats suggèrent que les réponses comportementales et physiologiques sont inter-reliées d’une manière multifactorielle et que la corticostérone joue un rôle clé dans la pathogénie des maladies psychiatriques.

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.

Decreased immobility in swimming test by homologous interferon-alpha in mice accompanied with increased cerebral tryptophan level and serotonin turnover

Animal models are used to decipher the pathophysiology of IFN-alpha-induced psychiatric complications in humans. However, the behavioral effects of IFN-alpha in rodents remain highly controversial. In contrast to homologous IFN-alpha, our recent study revealed that human IFN-alpha, which was used in many previous investigations, had no biological activity in mice. To evaluate the behavioral effects of homologous IFN-alpha in mice, adult C57BL/6J mice were treated with carrier-free murine IFN-alpha and tested on a number of behavioral paradigms. Surprisingly, contrary to previous reports, IFN-alpha treatment decreased the time spent immobile in the forced-swimming test after a single intraperitoneal injection at 2 x 10(6)IU/kg, whereas general locomotor activity was not altered. The elevated plus-maze (EPM) test showed a trend toward an increased anxiety profile in IFN-alpha-treated mice. The tail-suspension and light dark exploration test revealed no difference between IFN-alpha-treated and control animals. Interestingly, neurochemical analysis revealed significantly increased concentrations of tryptophan and 5-hydroxyindoleacetic acid (5-HIAA)/serotonin (5-HT) ratios following IFN-alpha treatment in selected brain regions. Thus, systemic murine IFN-alpha treatment increases swimming time in mice. Increased cerebral serotonin turnover as well as increased tryptophan concentrations, induced by IFN-alpha, implicates serotonergic neurotransmission in behavioral dysfunction caused by this innate immune mediator.

Cognitive dysfunction in HIV encephalitic SCID mice correlates with levels of Interferon-alpha in the brain

BACKGROUND

Interferon alpha (IFNalpha) is an antiviral cytokine produced in response to viral infection. IFNalpha also acts as a neuromodulatory molecule in the central nervous system (CNS). Elevated IFNalpha in the CNS causes cognitive deficits.

OBJECTIVE

To determine if elevated levels of IFNalpha in an HIV encephalitis mouse model correlate with cognitive deficits.

METHODS

C57BL/6J SCID mice were inoculated intracerebrally (i.c.) with HIV infected or uninfected (control) macrophages and cognitively tested in a water escape radial arm maze. After behavioral testing was completed, immunohistochemistry and ELISA were used to examine brain pathology and IFNalpha expression.

RESULTS

Mice injected i.c. with HIV infected macrophages exhibited significantly more working memory errors, particularly in trials with the highest memory load. Immunohistochemistry indicated increased mouse IFNalpha staining prevalent on neurons and glial cells in the brains of mice with HIV infected macrophages compared to mice with uninfected control macrophages. In addition, IFNalpha levels in the brain correlated directly with working memory errors for mice with HIV infected macrophages.

CONCLUSIONS

These data suggest that the cognitive deficit noted for the C57BL/6J SCID mice with HIV infected macrophages is mediated by the infection induced increase in IFNalpha.

The endomorphin system and its evolving neurophysiological role

Endomorphin-1 (Tyr-Pro-Trp-Phe-NH2) and endomorphin-2 (Tyr-Pro-Phe-Phe-NH2) are two endogenous opioid peptides with high affinity and remarkable selectivity for the mu-opioid receptor. The neuroanatomical distribution of endomorphins reflects their potential endogenous role in many major physiological processes, which include perception of pain, responses related to stress, and complex functions such as reward, arousal, and vigilance, as well as autonomic, cognitive, neuroendocrine, and limbic homeostasis. In this review we discuss the biological effects of endomorphin-1 and endomorphin-2 in relation to their distribution in the central and peripheral nervous systems. We describe the relationship between these two mu-opioid receptor-selective peptides and endogenous neurohormones and neurotransmitters. We also evaluate the role of endomorphins from the physiological point of view and report selectively on the most important findings in their pharmacology.

The widely-used anti-viral drug interferon-alpha induces depressive- and anxiogenic-like effects in healthy rats

Interferon-alpha (IFN-alpha) is a naturally occurring human cytokine that is a key therapy in the treatment of several viral diseases and cancers. However, treatment can produce significant neuropsychiatric and neurotoxic adverse events, including depression and anxiety. Here we investigated the effects of a clinically-comparable treatment regime of IFN-alpha on depressive- and anxiety-like behaviour in rats; and also examined frontal-cortical and hippocampal BDNF levels. Rats treated with IFN-alpha for four weeks showed significant increases in depressive- and anxiety-like behaviour. Further experimental investigation revealed that hedonic dysregulation (stronger preference for a sweet solution) did not emerge until the second week of treatment, and became more persistent as treatment progressed. No significant IFN-alpha-induced changes in BDNF levels were found. These results indicate that the affective deficits seen in patients may be modelled in healthy animals. This model may represent a novel tool to investigate the extent of and mechanisms underlying the IFN-alpha psychiatric syndrome.

Chronic intraperitoneal injection of interferon-alpha reduces serotonin levels in various regions of rat brain, but does not change levels of serotonin transporter mRNA, nitrite or nitrate

Interferon-alpha therapy is associated with a high rate of depression, but the pathophysiological mechanisms remain unclear. The purpose of the present study was to investigate the effects of i.p. administered interferon-alpha on monoaminergic neurotransmission in the brain. The levels of monoamines and associated metabolites were measured in various regions of the rat brain using a high-performance liquid chromatography-electrochemical detection system. The serotonin transporter mRNA levels were also measured using in situ hybridization. After 1 day, dopamine turnover was diminished in the cortex. Norepinephrine turnover was decreased in most regions tested after 4 days. However, these changes were transient. After 14 days, serotonin turnover was increased in the frontal cortex and hippocampus in rats given a dose of 20 000 IU/kg; in the frontal cortex, hippocampus, amygdala, thalamus, hypothalamus and brainstem in those on 200 000 IU/kg; and in the thalamus and hypothalamus in those on 2 000 000 IU/kg (all P < 0.05). However, 14-day treatment did not significantly change serotonin transporter mRNA levels. Next, the question of whether interferon-alpha affects monoamine levels via induction of nitric oxide (NO), was investigated. However, there were no changes in either NO2- or NO3-, as markers of NO production, in any brain regions after 14-day treatment. These results suggest that chronic peripheral administration of interferon-alpha induces metabolic changes in the central serotonin system. Further investigation is needed to determine exactly how this cytokine affects the central serotonin system and to assess whether a central serotonin abnormality is involved in interferon-induced depression.

Interferon and the central nervous system

Interferons (IFNs) were discovered as natural antiviral substances produced during viral infection and were initially characterized for their ability to "interfere" with viral replication, slow cell proliferation, and profound alteration of immunity. The IFNs are synthesized and secreted by monocytes, macrophages, T-lymphocytes, neurons, and glia cells. The different IFNs are classified into three classes: alpha, beta, and gamma. alpha-IFN produced in the brain exerts direct effects on the brain and endocrine system by activating the neurosecretory hypothalamic neurons and regulates the hypothalamic-pituitary-adrenocortical axis. IFNs modulate neurophysiological activities of many brain region involving in pain, temperature, and food intake regulation. alpha-IFN administration activates the sympathetic nerves innervating components of the immune system. IFNs may serve as regulatory mediators between the central nervous system, the immune system, and endocrine system. IFN is used as immunologic therapy to treat various hematologic malignancies and infectious ailments and autoimmune diseases.

Cytokines as mediators of depression: what can we learn from animal studies?

It has recently been postulated that cytokines may cause depressive illness in man. This hypothesis is based on the following observations: 1. Treatment of patients with cytokines can produce symptoms of depression; 2. Activation of the immune system is observed in many depressed patients; 3. Depression occurs more frequently in those with medical disorders associated with immune dysfunction; 4. Activation of the immune system, and administration of endotoxin (LPS) or interleukin-1 (IL-1) to animals induces sickness behavior, which resembles depression, and chronic treatment with antidepressants has been shown to inhibit sickness behavior induced by LPS; 5. Several cytokines can activate the hypothalamo-pituitary-adrenocortical axis (HPAA), which is commonly activated in depressed patients; 6. Some cytokines activates cerebral noradrenergic systems, also commonly observed in depressed patients; 7. Some cytokines activate brain serotonergic systems, which have been implicated in major depressive illness and its treatment. The evidence for each of these tenets is reviewed and evaluated along with the effects of cytokines in classical animal tests of depression. Although certain sickness behaviors resemble the symptoms of depression, they are not identical and each has distinct features. Thus the value of sickness behavior as an animal model of major depressive disorder is limited, so that care should be taken in extrapolating results from the model to the human disorder. Nevertheless, the model may provide insight into the etiology and the mechanisms underlying some symptoms of major depressive disorder. It is concluded that immune activation and cytokines may be involved in depressive symptoms in some patients. However, cytokines do not appear to be essential mediators of depressive illness.

Behavioral responses during the forced swim test are not affected by anti-inflammatory agents or acute illness induced by lipopolysaccharide

Pro-inflammatory cytokines and other molecules traditionally associated with immune function have been implicated in mediating behavioral and physiological consequences of stressor exposure. There is also evidence that cytokines are aberrantly expressed in depressive populations, suggesting they may play an etiological role in the development of depression/despair-related processes. Thus, we conducted a series of experiments to determine whether agents known to suppress cytokine activity or inflammatory responses in the CNS would alter the normal progression of behavioral responses during the forced swim test (FST, an animal model of depression/behavioral despair). Adult male Sprague-Dawley rats were injected with indomethacin (1 or 10 mg/kg intraperitoneally (i.p.)), alpha-MSH (0.25 or 0.5 microg icv), or minocycline (20 or 40 mg/kg i.p.) prior to each day of the FST and behavioral assessments were performed. Injection of indomethacin, alpha-MSH, or minocycline had no effect on the development of the immobility response during the FST on either day of testing. In a second series of experiments, we examined whether behavioral responses during forced swim would be affected by acute illness induced by a single injection of lipopolysaccharide (LPS). Acute injection of LPS (10 or 100 microg/kg i.p.) had no effect on behavioral responding during the FST irrespective of when it was injected, despite pronounced reductions in social behavior following these same doses of LPS. From these studies, we conclude that (a) endogenous inflammatory mediators do not appear to be involved in the normal progression of behavioral responses during the FST, and (b) behavioral responses during the FST are not affected by acute systemic injection of LPS.

The phenomenology and treatment of interferon-induced depression

Interferon (IFN)-alpha, IFN-beta, and IFN-gamma are currently available for the treatment of malignancies, viral infections (e.g., hepatitis C virus), multiple sclerosis (MS), and skin conditions. In addition to their therapeutic effects, IFNs commonly cause various side effects. Most common among the side effects of IFN are "flu-like" symptoms such as chills, fever, and muscle soreness. However, IFN can also cause significant neuropsychiatric side effects, particularly symptoms of depression. A literature search was conducted in order to summarize current information on (1) the frequency, characteristics, and risk factors of IFN-induced depression, (2) possible biochemical mechanisms associated with IFN-induced depression, and (3) the treatment strategies for IFN-induced depression. Review of the literature suggests that symptoms of depression induced by IFN therapy, in particular IFN-alpha therapy, are common and can limit the treatment utility, often necessitating discontinuation of IFN therapy or the use of psychopharmacologic agents. Depression is also a suspected side effect of therapy with IFN-beta and IFN-gamma; however, the association has not been as convincingly confirmed. Importantly, IFNs affect neurochemical pathways putatively involved in the etiology of depression. While these depressive side effects usually resolve after the completion of IFN therapy, they can persist or reappear with dose escalations. It is recommended that health care providers, patients and their families be informed about the potential risk of the psychiatric disturbances that can occur with IFN-alpha therapy. Screening and monitoring, ideally using symptom rating scales for depression, and early antidepressant treatment intervention appear necessary to optimize IFN therapy for the majority of patients.

The non-steroidal anti-inflammatory drug diclofenac sodium attenuates IFN-alpha induced alterations to monoamine turnover in prefrontal cortex and hippocampus

Interferon-alpha (IFN-alpha) administration induces major depression in a significant number of patients undergoing treatment for viral illnesses and other chronic diseases. Non-steroidal anti-inflammatory drugs (NSAIDs) are known to counteract a number of IFN-alpha-induced side effects, including pro-inflammatory cytokine activation and stress hormone release. To investigate this possibility further, we sought to determine the effect of the NSAID diclofenac sodium on monoamine turnover in brain induced by acute IFN-alpha exposure. Eleven male, Wistar rats (8 weeks old) were pretreated with diclofenac (20 mg/kg, s.c.) or saline, followed by intracerebroventricular (i.c.v.) infusion of IFN-alpha (1000 IU in 5 microl) or vehicle. The prefrontal cortex, striatum, and hippocampus were isolated and samples were assayed for monoamines and major metabolites by high-pressure liquid chromatography with electrochemical detection. The data show that acute IFN-alpha increased serotonin turnover in prefrontal cortex and increased dopamine turnover in hippocampus, while pre-treatment with diclofenac completely prevented these neurochemical responses. Importantly, these changes were recorded in two brain areas known to be important in depression and antidepressant action. These data offer support for a novel role of NSAIDs in modulating IFN-alpha-induced neurochemical alterations, and raise the possibility of the use of NSAIDs for the prevention of IFN-alpha-induced depression.

Endogenous opiates: 2000

This paper is the twenty-third installment of the annual review of research concerning the opiate system. It summarizes papers published during 2000 that studied the behavioral effects of the opiate peptides and antagonists, excluding the purely analgesic effects, although stress-induced analgesia is included. The specific topics covered this year include stress; tolerance and dependence; learning, memory, and reward; eating and drinking; alcohol and other drugs of abuse; sexual activity, pregnancy, and development; mental illness and mood; seizures and other neurological disorders; electrical-related activity; general activity and locomotion; gastrointestinal, renal, and hepatic function; cardiovascular responses; respiration and thermoregulation; and immunological responses.