Research report
Behavioral profile of P2X7 receptor knockout mice in animal models of depression and anxiety: Relevance for neuropsychiatric disorders

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Abstract

The purinergic P2X7 receptor is a ligand-gated ion channel found on peripheral macrophages and microglia in the nervous system. Activation of P2X7 receptors results in the rapid release of interleukin-1β (IL-1β). Cytokines like IL-1β are suggested to be involved in the pathophysiology of depression. The aim of this study was to behaviorally profile P2X7 receptor knockout (KO) mice in behavioral models of depression- and anxiety-like behaviors. P2X7 receptor KO and wild type (WT) mice were tested in multiple models including; forced swim test, tail suspension test, elevated plus maze, novelty suppressed feeding, spontaneous locomotor activity, and food intake. P2X7 receptor KO mice exhibited an antidepressant-like profile in tail suspension test and forced swim test; an effect that was not associated with changes in spontaneous locomotor activity. In addition, P2X7 receptor KO mice showed higher responsivity to a subefficacious dose of the antidepressant drug imipramine (15 mg/kg) in forced swim test. No significant differences between genotypes were observed in models of anxiety. These data support the relevance of pro-inflammatory cytokines in depressive-like states, and suggest that P2X7 receptor antagonists could be of potential interest for the treatment of affective disorders.

Introduction

Depression is recognized as having high prevalence in several medical conditions including infectious, autoimmune and neurodegenerative diseases. Over the last two decades an increasing body of evidence has indicated a strong relationship between depression and immunological dysfunction in depressed patients [5], [17], [42]. It has been suggested that excessive secretion of macrophage cytokines, interleukin-1β (IL-1β), interferon-α (INF-α) and tumor necrosis factor-α (TNF-α) could be a potential causative factor for the disorder [58]. Several lines of evidence support a role for cytokines in depression: depression is accompanied by signs of immune activation and elevated levels of pro-inflammatory cytokines [32], [49], [64], pro-inflammatory cytokines such as IL-1β, TNF-α, and IL-6 may produce “sickness behavior” and mediate many of the physiological and behavioral changes associated with depression [7], [16], [33], [51], cytokines can induce neuroendocrine and neurochemical changes similar to a depressive syndrome [20], [26], [33], [51], and clinical use of cytokines like IFN-α produces depressive-like symptoms that can be attenuated with antidepressant treatments [30].

The purinergic P2X receptors are ligand-gated ion channels activated by adenosine 5′-triphosphate (ATP) and other related nucleotides, and are formed by seven subunits that are encoded by different genes (P2X1–P2X7) [47]. Purinergic receptors are present in mammalian cells such as brain, autonomic and spinal cord neurons, glial cells and immune cells [47]. P2X7 receptors can modulate cell growth, proliferation, cause apoptosis and cell death [1], [23]. In addition, the P2X7 receptor can modulate the maturation and release of IL-1β in macrophages and microglia and is involved in general mechanisms implicated in inflammation and progression of neurodegenerative diseases [22], [24], [25], [29], [39].

The P2X7 receptor subunit gene in humans is located close to the tip of the long arm of chromosome 12. Previous genetic studies identified a susceptibility locus in the region of chromosome 12q23–24 that suggested a linkage with mood disorders such as bipolar disorder and major depressive disorder [2], [14], [38]. Recently, an increased vulnerability to bipolar affective disorders associated with single nucleotide polymorphisms in the chromosome 12q24.31 region that encodes for the P2X7 receptor gene has been reported [8], [56], [57].

In view of the involvement of P2X7 receptors in cytokine release, inflammation, and apoptotic cell death, it is reasonable to hypothesize that P2X7 receptors could play a role in the pathology of depression. Considering that cytokines like IL-1β can induce behavioral and physiological changes that resemble depression, that immune activation and altered levels of pro-inflammatory cytokines are associated with major depression, and that P2X7 receptors play an important role regulating the release of pro-inflammatory cytokines, it could be proposed that the inactivation of P2X7 receptors might result in antidepressant-like effects and might represent a potential target for the treatment of depression.

To investigate the role of P2X7 receptors in depression- and anxiety-like behaviors, mutant P2X7 receptor knockout (KO) mice and wild type (WT) mice were tested in several well characterized preclinical paradigms used to evaluate depression- and anxiety-like behaviors.

Section snippets

Generation of mutant P2X7 receptor knockout mice

The generation of P2X7 receptor gene KO mice has been previously described [31], [59]. These mice show altered ATP-stimulated cytokine processing [59] and reduced signs of experimental arthritis [31]. P2X7 receptor mutant mice used in the present studies were purchased from Lexicon Genetics Incorporated (The Woodlands, TX) and were generated based on previously established methodology [59]. The null targeting vector was derived using the Lambda knockout shuttle (KOS) system [65]. The Lambda KOS

Mouse peritoneal macrophages IL-1 release assay

To confirm that macrophages from P2X7 receptor KO mice lack the capacity to release IL-1β mediated by stimulation of P2X7 receptor [59], resident peritoneal macrophages from either WT or P2X7 receptor KO mice (n = 5/group) were primed with LPS and then stimulated with varying concentrations of BzATP (Fig. 1). In the WT mice, there was a dose related increase in the level of IL-1β released into the supernatant. When the macrophages from the P2X7 KO mice were stimulated with BzATP no measurable

Discussion

The inability of BzATP to stimulate the release of IL-1β peritoneal macrophages from P2X7 receptor KO mice relative to WT controls [59] was confirmed in the present study. Interestingly, the present data demonstrate that P2X7 receptor KO mice displayed antidepressant-like behaviors in two behavioral models: the tail suspension test and the forced swim test. In these models that are widely used for screening of antidepressant compounds [52], [61], P2X7 receptor KO mice exhibited significantly

Acknowledgement

This research has been funded by Abbott Laboratories.

References (68)

  • S. Hayley et al.

    The pathogenesis of clinical depression: stressor- and cytokine-induced alterations of neuroplasticity

    Neuroscience

    (2005)
  • S. Lanquillon et al.

    Cytokine production and treatment response in major depressive disorder

    Neuropsychopharmacology

    (2000)
  • S.J. Larson et al.

    Behavioral effects of cytokines

    Brain Behav Immun

    (2001)
  • A. Lin et al.

    The in vitro immunosuppressive effects of moclobemide in healthy volunteers

    J Affect Disord

    (2000)
  • A. MacKenzie et al.

    Rapid secretion of interleukin-1beta by microvesicle shedding

    Immunity

    (2001)
  • M. Maes

    Evidence for an immune response in major depression: a review and hypothesis

    Prog Neuropsychopharmacol Biol Psychiatry

    (1995)
  • Y.S. Mineur et al.

    Effects of unpredictable chronic mild stress on anxiety and depression-like behavior in mice

    Behav Brain Res

    (2006)
  • C. Mombereau et al.

    Altered response to benzodiazepine anxiolytics in mice lacking GABA B(1) receptors

    Eur J Pharmacol

    (2004)
  • J.T. Neary et al.

    Trophic actions of extracellular nucleotides and nucleosides on glial and neuronal cells

    Trends Neurosci

    (1996)
  • B.W. Penninx et al.

    Inflammatory markers and depressed mood in older persons: results from the Health Aging and Body Composition study

    Biol Psychiatry

    (2003)
  • A.S. Rossler et al.

    Chronic mild stress alleviates anxious behaviour in female mice in two situations

    Behav Processes

    (2000)
  • R.S. Smith

    The macrophage theory of depression

    Med Hypotheses

    (1991)
  • M. Solle et al.

    Altered cytokine production in mice lacking P2X(7) receptors

    J Biol Chem

    (2001)
  • O. Stork et al.

    Postnatal development of a GABA deficit and disturbance of neural functions in mice lacking GAD65

    Brain Res

    (2000)
  • Z. Xia et al.

    Tricyclic antidepressants inhibit IL-6 IL-1 beta and TNF-alpha release in human blood monocytes and IL-2 and interferon-gamma in T cells

    Immunopharmacology

    (1996)
  • R. Yirmiya et al.

    Effects of antidepressant drugs on the behavioral and physiological responses to lipopolysaccharide (LPS) in rodents

    Neuropsychopharmacology

    (2001)
  • M.P. Abbracchio et al.

    Purinergic signalling: pathophysiological roles

    Jpn J Pharmacol

    (1998)
  • H. Anisman et al.

    Anhedonic and anxiogenic effects of cytokine exposure

    Adv Exp Med Biol

    (1999)
  • H. Anisman et al.

    Cytokines, stress and depressive illness: brain-immune interactions

    Ann Med

    (2003)
  • H. Anisman et al.

    Cytokines as a precipitant of depressive illness: animal and human studies

    Curr Pharm Des

    (2005)
  • N. Barden et al.

    Analysis of single nucleotide polymorphisms in genes in the chromosome 12Q24 31 region points to P2RX7 as a susceptibility gene to bipolar affective disorder

    Am J Med Genet B Neuropsychiatr Genet

    (2006)
  • S.R. Bodnoff et al.

    The effects of chronic antidepressant treatment in an animal model of anxiety

    Psychopharmacology (Berl)

    (1988)
  • D. Curtis et al.

    Genome scan of pedigrees multiply affected with bipolar disorder provides further support for the presence of a susceptibility locus on chromosome 12q23–q24, and suggests the presence of additional loci on 1p and 1q

    Psychiatr Genet

    (2003)
  • R. Dantzer

    Cytokine-induced sickness behavior: mechanisms and implications

    Ann N Y Acad Sci

    (2001)
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