Yehuda Pollak

Illness, Cytokines, and Depression

Abstract: Various medical conditions that involve activation of the immune system are associated with psychological and neuroendocrine changes that resemble the characteristics of depression. In this review we present our recent studies, designed to investigate the relationship between the behavioral effects of immune activation and depressive symptomatology. In the first set of experiments, we used a double‐blind prospective design to investigate the psychological consequences of illness in two models: (1) vaccination of teenage girls with live attenuated rubella virus, and (2) lipopolysaccharide (LPS) administration in healthy male volunteers. In the rubella study, we demonstrated that, compared to control group subjects and to their own baseline, a subgroup of vulnerable individuals (girls from low socioeconomic status) showed a significant virus‐induced increase in depressed mood up to 10 weeks after vaccination. In an ongoing study on the effects of LPS, we demonstrated significant LPS‐induced elevation in the levels of depression and anxiety as well as memory deficits. These psychological effects were highly correlated with the levels of LPS‐induced cytokine secretion. In parallel experiments, we demonstrated in rodents that immune activation with various acute and chronic immune challenges induces a depressive‐like syndrome, characterized by anhedonia, anorexia, body weight loss, and reduced locomotor, exploratory, and social behavior. Chronic treatment with antidepressants (imipramine or fluoxetine) attenuated many of the behavioral effects of LPS, as well as LPS‐induced changes in body temperature, adrenocortical activation, hypothalamic serotonin release, and the expression of splenic TNF‐α mRNA. Taken together, these findings suggest that cytokines are involved in the etiology and symptomatology of illness‐associated depression.

Cytokines, “Depression Due to A General Medical Condition,” and Antidepressant Drugs

Activation of the immune system during various medical conditions produces neural, neuroendocrine, and behavioral effects. The psychological and physiological effects of immune activation resemble many characteristics of depression. The essential features of depression are depressed mood and loss of interest or pleasure in all, or almost all activities (anhedonia). Several associated symptoms are also present, including, appetite disturbance, change in body weight, sleep disturbance, psychomotor disturbance, fatigue, loss of energy, and difficulty in thinking or concentrating (DSM-IV, 1994). Depression is also characterized by specific alterations in the functioning of neurochemical and neuroendocrine systems, including monoaminergic systems and the hypothalamic-pituitary-adrenal (HPA) axis (Brown, Steinberg, & van Praag, 1994; Holsboer, 1995). Most of these psychological and neuroendocrine symptoms appear both in humans and animals during diseases that involve immune activation. Based on these findings, and on several additional lines of evidence that will be presented below, we have recently argued that immune activation is involved in the etiology and symptomatology of depression associated with various medical conditions (Yirmiya, 1997).

Effects of Antidepressant Drugs on the Behavioral and Physiological Responses to Lipopolysaccharide (LPS) in Rodents

Antidepressants produce various immunomodulatory effects, as well as an attenuation of the behavioral responses to immune challenges, such as lipopolysaccharide (LPS). To explore further the effects of antidepressants on neuroimmune interactions, rats were treated daily with either fluoxetine (Prozac) or saline for 5 weeks, and various behavioral, neuroendocrine, and immune functions were measured following administration of either LPS or saline. Chronic fluoxetine treatment significantly attenuated the anorexia and body weight loss, as well as the depletion of CRH-41 from the median eminence and the elevation in serum corticosterone levels induced by LPS. Chronic treatment with imipramine also attenuated LPS-induced adrenocortical activation. In rats and in mice, which normally display a biphasic body temperature response to LPS (initial hypothermia followed by hyperthermia), chronic treatment with fluoxetine completely abolished the hypothermic response and facilitated and strengthened the hyperthermic response. The effects of antidepressants on the responsiveness to LPS are probably not mediated by their effects on peripheral proinflammatory cytokine production, because LPS-induced expression of TNFα and IL-1β mRNA in the spleen (assessed by semiquantitative in situ hybridization) was not altered following chronic treatment with either fluoxetine or imipramine. The effects of antidepressants on the acute phase response may have important clinical implications for the psychiatric and neuroendocrine disturbances that are commonly associated with various medical conditions.

Cytokine-induced changes in mood and behaviour : implications for 'depression due to a general medical condition', immunotherapy and antidepressive treatment

Several lines of evidence indicate that cytokine-mediated communication pathways between the immune system and the brain are involved in the pathophysiology of depression: (1) . Depression is highly prevalent in various medical conditions, including infectious, autoimmune and neurodegenerative diseases. This clinical association cannot be attributed solely to psychological distress, and it probably reflects direct activation of illness-induced physiological processes. (2). Experiments in humans and in animals demonstrate that exposure to cytokines induces depressive-like mood and behavioural alterations. (3). Cytokine immunotherapy in cancer and hepatitis patients elicits a major depressive episode in a large percentage of the patients. (4). Several types of depression that are not directly associated with a physical disease (e.g. major depression, melancholia, dysthymia) were also associated with cytokine hypersecretion. (5). Antidepressant drugs possess anti-inflammatory characteristics, which may partly account for their therapeutic effect. Congruently, antidepressants were found to reverse cytokine-induced major depression in humans and depressive-like behaviours in animals. (6). Cytokines affect brain systems that were implicated in the aetiology of depression, including the hypothalamus-pituitary-adrenal axis and monoaminergic systems. These conclusions strongly suggest that during medical conditions elevated levels of cytokines directly contribute to the induction of depression. Therefore, illness-associated depression should not be underestimated (in terms of prevalence and severity), and should be treated with antidepressant drugs, which may act on the specific physiological mechanisms of this disorder.

Acetylcholinesterase inhibitors reduce brain and blood interleukin‐1β production

Overproduction of interleukin‐1 within the brain is associated with Alzheimers disease and other neurological conditions. We report that peripheral administration of the acetylcholinesterase inhibitors tacrine, rivastigmine, neostigmine, or EN101 (an antisense oligonucleotide directed at acetylcholinesterase messenger RNA) to mice significantly attenuated the production of interleukin‐1β in the hippocampus and blood, concomitantly with the reduction in acetylcholinesterase activity. These findings demonstrate that cholinergic enhancement produces central and peripheral antiinflammatory effects and suggest a novel therapeutic mechanism for acetylcholinesterase inhibitors. Ann Neurol 2005

Neuronal overexpression of ‘readthrough’ acetylcholinesterase is associated with antisense-suppressible behavioral impairments

Molecular origin(s) of the diverse behavioral responses to anticholinesterases were explored in behaviorally impaired transgenic (Tg) FVB/N mice expressing synaptic human acetylcholinesterase (hAChE-S). Untreated hAChE-S Tg, unlike naïve FVB/N mice, presented variably intense neuronal overexpression of the alternatively spliced, stress-induced mouse ‘readthrough’ mAChE-R mRNA. Both strains displayed similar diurnal patterns of locomotor activity that were impaired 3 days after a day-to-night switch. However, hAChE-S Tg, but not FVB/N mice responded to the circadian switch with irregular, diverse bursts of increased locomotor activity. In social recognition tests, controls displayed short-term recognition, reflected by decreased exploration of a familiar, compared to a novel juvenile conspecific as well as inverse correlation between social recognition and cortical and hippocampal AChE specific activities. In contrast, transgenics presented poor recognition, retrievable by tetrahydroaminoacridine (tacrine, 1.5 mg kg−1). Tacrines effect was short-lived (<40 min), suggesting its effect was overcome by anticholinesterase-induced overproduction of mache-r. consistent with this hypothesis, antisense oligonucleotides (two daily intracerebroventricular injections of 25 ng) arrested mache-r synthesis, selectively reduced mache-r levels and afforded an extended (>24 h) suppression of the abnormal social recognition pattern in transgenics. Efficacy of antisense treatment was directly correlated with AChE-R levels and the severity of the impaired phenotype, being most apparent in transgenics presenting highly abnormal pre-treatment behavior. These findings demonstrate that neuronal AChE-R overproduction is involved in various behavioral impairments and anticholinesterase responses, and point to the antisense strategy as a potential approach for re-establishing cholinergic balance.

Behavioral aspects of experimental autoimmune encephalomyelitis.

Acute inflammation is known to induce a depressive-like sickness behavior syndrome in humans and in experimental animals. In the present study, we sought to determine whether a chronic neuroautoimmune inflammation is also associated with a similar behavioral syndrome. Experimental autoimmune encephalomyelitis (EAE) was induced in SJL/J female mice by adoptive transfer of lymph node cells, and sickness behavior symptoms, including anorexia, loss of body weight, reduced social exploration, and decreased preference for sucrose solution were measured. We report that these components of sickness behavior were induced during the acute phase of the disease, and recovered in later phases. Moreover, the onset and recovery of the behavioral symptoms preceded the onset and recovery of the neurological signs, respectively. Since EAE is considered a model for multiple sclerosis (MS), it is suggested that EAF-induced behavioral changes may serve as a model for the depressive symptomatology that characterizes most MS patients.

The Utility of a Continuous Performance Test Embedded in Virtual Reality in Measuring ADHD-Related Deficits

Objective: Continuous performance tasks (CPT) are popular in the diagnostic process of Attention Deficit/Hyperactivity Disorder (ADHD), providing an objective measure of attention for a disorder with otherwise subjective criteria. Aims of the study were to: (1) compare the performance of children with ADHD on a CPT embedded within a virtual reality classroom (VR-CPT) to the currently used Test of Variables of Attention (TOVA) CPT, and (2) assess how the VR environment is experienced. Methods: Thirty-seven boys, 9 to 17 years, with (n = 20) and without ADHD (n = 17) underwent 3 CPT’s: VR-CPT, the same CPT without VR (No VR-CPT) and the TOVA. Immediately following CPT, subjects described their subjective experiences on the Short Feedback Questionnaire. Results were analyzed using analysis of variance with repeated measures. Results: Children with ADHD performed poorer on all CPT’s. The VR-CPT showed similar effect sizes to the TOVA. Subjective feelings of enjoyment were most positive for VR-CPT. Conclusion: The VR-CPT is a sensitive and user-friendly assessment tool to aid diagnosis in ADHD.

Why do young women smoke? V. Role of direct and interactive effects of nicotinic cholinergic receptor gene variation on neurocognitive function

Previous work suggests that young women who smoke cigarettes regularly, or did so in the past, manifest a neurocognitive profile that is characterized by small but significant impairments of response inhibition and attention. The present study sought to determine whether variation in nicotinic cholinergic receptor (nAchR) genes impacts upon cognitive function in these domains by overall or differential effects on the performance of current, former and non‐smokers. The study sample consisted of 100 female college students, current or past smokers, and 144 who had never smoked. All performed a computerized neurocognitive test battery and were genotyped for 39 single nucleotide polymorphisms in 11 nAchR genes. The results, derived from linear or logistic regression, show significant direct and interactive relationships between single nucleotide polymorphisms and haplotypes in several nAchR genes and performance on the Matching Familiar Figures Test (MFFT) Stroop test, Continuous Performance Task (CPT) and Tower of London (TOL) test. Response inhibition (MFFT, Stroop, CPT Loading Phase, TOL) was associated with variants in CHRNA2, CHRNA4, CHRNA5, CHRNA7, CHRNA9, CHRNA10, CHRNB2 and CHRNB3. Selective attention (Stroop) was associated with CHRNA4, CHRNA5, CHRNA9 and CHRNB2. Sustained attention (CPT Boring Phase) was associated with CHRNA4, CHRNA5, CHRNA7, CHRNA10 and CHRNB3. Up to 37% of the variance among the smokers and up to 47% of the variance among the non‐smokers on the test measures was explained. Differences between smokers and non‐smokers in neurocognitive function, putatively implicated in susceptibility to nicotine dependence, may be modulated by variants in nAchR genes, with potential implications for prevention and treatment.

Experimental autoimmune encephalomyelitis-associated behavioral syndrome as a model of 'depression due to multiple sclerosis'.

Many medical conditions, including inflammatory diseases such as multiple sclerosis (MS), are often accompanied by a high prevalence of depressive episodes. Inflammatory mediators, such as cytokines, were implicated in illness-associated depressive conditions, both in humans and in animals. For example, MS-associated depression (MSD) was attributed to pathophysiological processes such as immune dysregulation and cerebral inflammation. We have recently documented a depressive-like behavioral syndrome in mice with experimental autoimmune encephalomyelitis (EAE), an established model of MS. In the present paper, we discuss the similarities between the EAE-associated behavioral syndrome (EBS) and MSD, in terms of phenomenology, putative mechanisms and responsiveness to anti-depressive therapy. In particular, we show that: (1) EAE and depression are associated not only with similar behavioral symptomatology, but also with common physiological alterations, including impaired serotonergic neurotransmission, and activation of neuroendocrine (e.g., adrenocortical) and inflammatory cytokine systems; (2) the EBS precedes any neurological deficit during the initial EAE attack, as well as further exacerbations, and remits during recovery and between relapses. Similarly, in many MS patients depression precedes and accompanies the attacks and wanes during remissions; (3) females show increased susceptibility to EBS. Similarly, depression is much more prevalent in women than in men; (4) chronic treatment with the tricyclic anti-depressant imipramine reduced EAE-induced mortality, body-weight loss and behavioral suppression. Similarly, anti-depressant drugs have been used effectively in treating MSD. These findings suggest that the EBS may serve as an animal model for MSD.