Neural and behavioral responses to low-grade inflammation

doi:10.1016/j.bbr.2012.07.038

Behavioural Brain Research

Volume 235, Issue 2, 1 December 2012, Pages 334-341

https://doi.org/10.1016/j.bbr.2012.07.038 Get rights and content

Abstract

Neural and behavioral responses after peripheral immune challenge have been observed in numerous studies. The majority of these studies have utilized relatively high doses of lipopolysaccharide (LPS) as the immune stimulant. Little attention has been given to the effects of LPS dose ranges that simulate low grade-inflammation. The current studies were designed to characterize neural and behavioral responses following low-dose LPS stimulation. Results show burrowing and open field activity was significantly impaired following a single i.p. injection of 10, but not 1, μg/kg of LPS. In addition, following repeated 1 μg/kg LPS administration for 10 days, animals showed the progressive development of motor deficits over time. To correlate behavior with CNS activity, cFos activation was determined in the paraventricular nucleus, nucleus of the solitary tract, central amygdaloid nucleus, and ventrolateral medulla. Data revealed there was a dose-dependent activation in all brain areas examined, but only the PVN showed significant activation by low-dose LPS. Additionally, animals that received 1 μg/kg of LPS for 8 days had PVN cFos activation similar to animals that received a single 10 μg/kg LPS injection. These data demonstrate neural and behavior responses can be induced by low-grade inflammation and chronic exposure to sub-threshold levels of LPS can precipitate significantly heightened neural and behavioral responses.

Highlights

► Acute 10 μg/kg of LPS causes sickness behavior, but 1 μg/kg does not. ► Chronic low-dose LPS causes progressive deficits in open field not burrowing. ► Open field is the most sensitive test following chronic low grade inflammation. ► Dose response cFos activation of the PVN, NTS, CeA and VLM is apparent after LPS. ► Chronic low-dose LPS causes a potentiated PVN cFos activation.

Introduction

Increasing evidence from clinical studies suggests a strong link between inflammation and the development of numerous psychological disorders, including major depression [1], [2], anxiety disorders [3], and autism [4]. To reveal how inflammation might cause behavioral abnormalities exhibited in these disorders, many studies have used bacterial endotoxin lipopolysaccharide (LPS) as the inflammatory stimulant to induce inflammation. It has been documented that a single intraperitoneal (i.p.) injection of a septic dose of LPS indeed causes depressive-like behaviors [5], [6], increased anxiety [7], and reduced social interaction [8] in experimental animals.

However, such use of septic doses of LPS to mimic the pathogenesis of psychological disorders may lack both face validity and construct validity. Human psychological disorders are not triggered by acute septic shock and levels of inflammatory cytokines reported in patients with psychological disorders are often higher than normal [9], [10], [11], but orders of magnitude lower than those induced by septic shock [12], [13], [14], [15], [16]. The levels of inflammatory cytokines in patients with various psychological disorders are actually more in line with those in patients with low-grade inflammation [17], [18]. Whether low-grade inflammation induces neural and behavioral responses relevant to the pathogenesis of psychological disorders has not been investigated.

In this study, we induced low-grade inflammation by injecting low doses of LPS intraperitoneally. The results demonstrate low-grade inflammation causes specific neuronal activation patterns in the brain that correspond to alterations in behavior.

Section snippets

Subjects

Subjects were 8–13 week-old male inbred FVB mice purchased from Charles River Laboratories (Wilmington, MA). Animals were allowed to acclimate in the animal facility for ∼1 week prior to experimental procedures. Mice were group housed 5/cage in standard polycarbonate mouse cages and maintained on a 12 h light/dark cycle with lights being turned on at 0600 in an AAALAC (American Association of Accreditation of Laboratory Animal Care) facility. Food and water was available ad libitum unless

Central cFos activation following low and high-dose peripheral LPS

Activation of cFos in the PVN, NTS, CeA, and VLM 3 h after i.p. injection of varying doses of LPS was evaluated. There were significant main effects of LPS treatment on the mean number of cFos labeled cells in the PVN, NTS, CeA and VLM (F(3,10) = 34.64; p < 0.0001; F(3,9) = 13.06; p < 0.001; F(3,9) = 4.22; p < 0.05; F(3,9) = 3.72; p < 0.05, respectively; see Fig. 1B, D, F, and H). Fisher's PLSD post hoc analyses for the PVN revealed that a single 10 μg/kg i.p. injection of LPS was sufficient to cause a

Discussion

Many affective disorders have been attributed to underlying inflammatory dysfunction. Clinical observations showed patients with mood disorders such as depression, anxiety, and autism have increased basal levels of circulating proinflammatory cytokines. In addition, experimental evidence from animal studies showed a single injection of high-dose bacterial mimics (i.e., LPS) induce both peripheral inflammation and behavioral deficits similar to those seen in affective disorders. These findings

Acknowledgements

This work was supported in full by the NIH grants: RO1 MH-046801-JFS, T32 DE-014320-JFS, F32 DE-022230-AJT, and RO1 AI-076926-NQ.

References (35)

A.H. Miller et al.
Inflammation and its discontents: the role of cytokines in the pathophysiology of major depression
Biological Psychiatry
(2009)
C. Onore et al.
The role of immune dysfunction in the pathophysiology of autism
Brain, Behavior, and Immunity
(2012)
F. Kaestner et al.
Different activation patterns of proinflammatory cytokines in melancholic and non-melancholic major depression are associated with HPA axis activity
Journal of Affective Disorders
(2005)
M. Maes et al.
Evidence for inflammation and activation of cell-mediated immunity in Myalgic Encephalomyelitis/Chronic Fatigue Syndrome (ME/CFS): increased interleukin-1, tumor necrosis factor-alpha, PMN-elastase, lysozyme and neopterin
Journal of Affective Disorders
(2012)
J.L. Teeling et al.
Sub-pyrogenic systemic inflammation impacts on brain and behavior, independent of cytokines
Brain, Behavior, and Immunity
(2007)
R.M. Deacon
Burrowing: a sensitive behavioural assay, tested in five species of laboratory rodents
Behavioural Brain Research
(2009)
M. Maes et al.
Increased serum IL-6 and IL-1 receptor antagonist concentrations in major depression and treatment resistant depression
Cytokine
(1997)
S.C. Datta et al.
Lipopolysaccharide-induced increases in cytokines in discrete mouse brain regions are detectable using Luminex xMAP technology
Journal of Neuroscience Methods
(2008)
R. Dantzer et al.
Neural and humoral pathways of communication from the immune system to the brain: parallel or convergent
Autonomic Neuroscience
(2000)
N. Quan et al.
Brain-immune communication pathways
Brain, Behavior, and Immunity
(2007)

H. Zhang et al.

Localized inflammation in peripheral tissue signals the CNS for sickness response in the absence of interleukin-1 and cyclooxygenase-2 in the blood and brain

Neuroscience

(2008)

R.P. Gaykema et al.

Organization of immune-responsive medullary projections to the bed nucleus of the stria terminalis, central amygdala, and paraventricular nucleus of the hypothalamus: evidence for parallel viscerosensory pathways in the rat brain

Brain Research

(2007)

N. Belevych et al.

Location-specific activation of the paraventricular nucleus of the hypothalamus by localized inflammation

Brain, Behavior, and Immunity

(2010)

M.A. Erickson et al.

Cytokine and chemokine responses in serum and brain after single and repeated injections of lipopolysaccharide: multiplex quantification with path analysis

Brain, Behavior, and Immunity

(2011)

F.E. Lotrich et al.

The role of inflammation in the pathophysiology of depression: different treatments and their effects

The Journal of Rheumatology. Supplement

(2011)

Z.A. Usmani et al.

Pharmacological interventions for the treatment of anxiety disorders in chronic obstructive pulmonary disease

Cochrane Database of Systematic Reviews

(2011)

J.P. Konsman et al.

Central nervous action of interleukin-1 mediates activation of limbic structures and behavioural depression in response to peripheral administration of bacterial lipopolysaccharide

The European Journal of Neuroscience

(2008)

Cited by (39)

The inflammatory response to birth requires MyD88 and is driven by both mother and offspring
2024, Brain, Behavior, and Immunity
Birth is an inflammatory event for the newborn, characterized by elevations in interleukin (IL)-6, IL-10, and tumor necrosis factor (TNF)-α peripherally and/or centrally, as well as changes in brain microglia. However, the mechanism(s) underlying these responses is unknown. Toll-like receptors (TLRs) play crucial roles in innate immunity and initiate inflammatory cascades upon recognition of endogenous or exogenous antigens. Most TLR signaling depends on the adaptor molecule myeloid differentiation primary response 88 (MyD88). We independently varied MyD88 gene status in mouse dams and their offspring to determine whether the inflammatory response to birth depends on MyD88 signaling and, if so, whether that signaling occurs in the offspring, the mother, or both. We find that the perinatal surges in plasma IL-6 and brain expression of TNF-α depend solely on MyD88 gene status of the offspring, whereas postnatal increases in plasma IL-10 and TNF-α depend on MyD88 in both the pup and dam. Interestingly, MyD88 genotype of the dam primarily drives differences in offspring brain microglial density and has robust effects on developmental neuronal cell death. Milk cytokines were evaluated as a possible source of postnatal maternal influence; although we found high levels of CXCL1/GROα and several other cytokines in ingested post-partum milk, their presence did not require MyD88. Thus, the inflammatory response previously described in the late-term fetus and newborn depends on MyD88 (and, by extension, TLRs), with signaling in both the dam and offspring contributing. Unexpectedly, naturally-occuring neuronal cell death in the newborn is modulated primarily by maternal MyD88 gene status.
Fetal brain vulnerability to SARS-CoV-2 infection
2023, Brain, Behavior, and Immunity
Whether or not SARS-CoV-2 can cross from mother to fetus during a prenatal infection has been controversial; however, recent evidence such as viral RNA detection in umbilical cord blood and amniotic fluid, as well as the discovery of additional entry receptors in fetal tissues suggests a potential for viral transmission to and infection of the fetus. Furthermore, neonates exposed to maternal COVID-19 during later development have displayed neurodevelopmental and motor skill deficiencies, suggesting the potential for consequential neurological infection or inflammation in utero. Thus, we investigated transmission potential of SARS-CoV-2 and the consequences of infection on the developing brain using human ACE2 knock-in mice. In this model, we found that viral transmission to the fetal tissues, including the brain, occurred at later developmental stages, and that infection primarily targeted male fetuses. In the brain, SARS-CoV-2 infection largely occurred within the vasculature, but also within other cells such as neurons, glia, and choroid plexus cells; however, viral replication and increased cell death were not observed in fetal tissues. Interestingly, early gross developmental differences were observed between infected and mock-infected offspring, and high levels of gliosis were seen in the infected brains 7 days post initial infection despite viral clearance at this time point. In the pregnant mice, we also observed more severe COVID-19 infections, with greater weight loss and viral dissemination to the brain, compared to non-pregnant mice. Surprisingly, we did not observe an increase in maternal inflammation or the antiviral IFN response in these infected mice, despite showing clinical signs of disease. Overall, these findings have concerning implications regarding neurodevelopment and pregnancy complications of the mother following prenatal COVID-19 exposure.
Ovariectomy in mice primes hippocampal microglia to exacerbate behavioral sickness responses
2023, Brain, Behavior, and Immunity - Health
Estrogens are a group of steroid hormones that promote the development and maintenance of the female reproductive system and secondary sex characteristics. Estrogens also modulate immune responses; estrogen loss at menopause increases the risk of inflammatory disorders. Elevated inflammatory responses in the brain can lead to affective behavioral changes, which are characteristic of menopause. Thus, here we examined whether loss of estrogens sensitizes microglia, the primary innate immune cell of the brain, leading to changes in affective behaviors. To test this question, adult C57BL/6 mice underwent an ovariectomy to remove endogenous estrogens and then received estradiol hormone replacement or vehicle. After a one-month recovery, mice received an immune challenge with lipopolysaccharide (LPS) or vehicle control treatment and underwent behavioral testing. Ovariectomized, saline-treated mice exhibited reduced social investigation compared to sham-operated mice. Furthermore, ovariectomized mice that received LPS exhibited an exacerbated decrease in sucrose preference, which was ameliorated by estradiol replacement. These results indicate that ovariectomy modulates affective behaviors at baseline and in response to an inflammatory challenge. Ovariectomy-related behavioral changes were associated with downregulation of Cx3cr1, a microglial receptor that limits activation, suggesting that estrogen loss can disinhibit microglia to immune stimuli. Indeed, estradiol treatment reduced ovariectomy-induced increases in Il1b and Il6 expression after an immune challenge. Changes in microglial reactivity following ovariectomy are likely subtle, as overt changes in microglial morphology (e.g., soma size and branching) were limited. Collectively, these results suggest that a lack of estrogens may allow microglia to confer exaggerated neuroimmune responses, thereby raising vulnerability to adverse affective- and sickness-related behavioral changes.
Birth triggers an inflammatory response in the neonatal periphery and brain
2022, Brain, Behavior, and Immunity
Citation Excerpt :
Peripheral inflammation is communicated to the brain via several routes (Dantzer, 2018; Hosoi et al., 2002; Silverman et al., 2005), suggesting that the inflammatory events of birth could affect the perinatal brain. Brain regions such as the paraventricular nucleus of the hypothalamus (PVN) and the hippocampus play important roles in coordinating the neural response to an immune challenge and are activated by peripheral inflammation (Elmquist and Saper, 1996; Frenois et al., 2007; Hoogland et al., 2015; Sawchenko et al., 1996; Tarr et al., 2012; Whylings et al., 2021). Even low-grade inflammation activates the PVN (Tarr et al., 2012), and we previously found marked activation of PVN neurons at birth in mice (Hoffiz et al., 2021).
Birth is preceded by inflammation at the fetal/maternal interface. Additionally, the newborn experiences stimuli that under any other circumstance could elicit an immune response. It is unknown, however, whether birth elicits an inflammatory response in the newborn that extends to the brain. Moreover, it is unknown whether birth mode may alter such a response. To study these questions, we first measured corticosterone and pro- and anti-inflammatory cytokines in plasma of mouse offspring at several timepoints spaced closely before and after a vaginal or Cesarean birth. We found highest levels of IL-6 one day before birth and surges in corticosterone and IL-10 just after birth, regardless of birth mode. We next examined the neuroimmune response by measuring cytokine mRNA expression and microglial number and morphology in the paraventricular nucleus of the hypothalamus and hippocampus around the time of birth. We found a marked increase in TNF-α expression in both brain regions a day after birth, and rapid increases in microglial cell number in the first three days postnatal, with subtle differences by birth mode. To test whether the association between birth and cytokine production or expansion of microglia is causal, we manipulated birth timing. Remarkably, advancing birth by a day advanced the increases in all of the markers tested. Thus, birth triggers an immune response in the body and brain of offspring. Our results may provide a mechanism for effects of birth (e.g., acute changes in cell death and neural activation) previously reported in the newborn brain.
Lipopolysaccharide-induced inflammation leads to acute elevations in pro-inflammatory cytokine expression in a mouse model of Fragile X syndrome
2020, Physiology and Behavior
Citation Excerpt :
The heightened expression in IL-1β and IL-6 may not be a robust enough inflammatory response to result in changes in how Fmr1 KO mice behaviorally respond to an immune stimulus. It is possible the lack of difference could be attributed to a floor effect, as much lower doses of LPS can induce sickness behavior and disrupt innate burrowing in mice [11, 31, 61]. However, it could also be that despite elevations in pro-inflammatory cytokines, Fmr1 KO mice are still capable of recovering from an immune stimulus similar to controls and that the presence of immune dysregulation does not negatively impact their behavioral phenotype.
Fragile X syndrome (FXS) is a neurodevelopmental disorder caused by a single genetic mutation in the Fmr1 gene, serving as the largest genetic cause of intellectual disability. Trinucleotide expansion mutations in Fmr1 result in silencing and hypermethylation of the gene, preventing synthesis of the RNA binding protein Fragile X mental retardation protein which functions as a translational repressor. Abnormal immune responses have been demonstrated to play a role in FXS pathophysiology, however, whether these alterations impact how those with FXS respond to an immune insult behaviorally is not entirely known. In the current study, we examine how Fmr1 knockout (KO) and wild type (WT) mice respond to the innate immune stimulus lipopolysaccharide (LPS), both on a molecular and behavioral level, to determine if Fmr1 mutations impact the normal physiological response to an immune insult. In response to LPS, Fmr1 KO mice had elevated hippocampal IL-1β and IL-6 mRNA levels 4 h post-treatment compared to WT mice, with no differences detected in any cytokines at baseline or between genotypes 24 h post-LPS administration. Fmr1 KO mice also had upregulated hippocampal BDNF gene expression 4 h post-treatment compared to WT mice, which was not dependent on LPS administration. There were no differences in hippocampal protein expression between genotypes in microglia (Iba1) or astrocyte (GFAP) reactivity. Further, both genotypes displayed the typical sickness response following LPS stimulation, demonstrated by a significant reduction in food burrowed by LPS-treated mice in a burrowing task. Additional investigation is critical to determine if the transient increases in cytokine expression could lead to long-term changes in downstream molecular signaling in FXS.
Immunomodulatory T cell death associated gene-8 (TDAG8) receptor in depression-associated behaviors
2019, Physiology and Behavior
Citation Excerpt :
Stress and negative emotion upregulate cytokine concentrations in humans [18]. In rodents, administration of cytokines at levels associated with inflammation or lipopolysaccharide (LPS), which promotes cytokine release, leads to depression-like behaviors [19–21]. Interestingly, treatment with antidepressants reduces plasma cytokines in both humans and rodents [13,22–24].
Converging evidence supports neuroimmune factors in depression psychopathology. We previously reported reduced depression-like behavior in immunomodulatory G-protein-coupled receptor, T cell death-associated gene-8 (TDAG8) deficient mice. Here, we expand on those findings by investigating depression- and anxiety-associated behaviors, and cytokine profiles in TDAG8-deficient mice. TDAG8-deficiency reduced depression- and anxiety-associated behaviors in the forced swim test (FST), open-field test and elevated zero maze. Interestingly, cytokine expression, particularly IL-6, was attenuated within hippocampus and spleen in TDAG8-deficient mice following the FST. There were no differences in immune-cell frequencies. Collectively, these data suggest a contributory role of TDAG8 in neuroimmune regulation and depression-associated physiology.

View all citing articles on Scopus

View full text

Research reportNeural and behavioral responses to low-grade inflammation

Abstract

Highlights

Introduction

Section snippets

Subjects

Central cFos activation following low and high-dose peripheral LPS

Discussion

Acknowledgements

Biological Psychiatry

Brain, Behavior, and Immunity

Journal of Affective Disorders

Journal of Affective Disorders

Brain, Behavior, and Immunity

Behavioural Brain Research

Cytokine

Journal of Neuroscience Methods

Autonomic Neuroscience

Brain, Behavior, and Immunity

Neuroscience

Brain Research

Brain, Behavior, and Immunity

Brain, Behavior, and Immunity

The role of inflammation in the pathophysiology of depression: different treatments and their effects

The Journal of Rheumatology. Supplement

Pharmacological interventions for the treatment of anxiety disorders in chronic obstructive pulmonary disease

Cochrane Database of Systematic Reviews

Central nervous action of interleukin-1 mediates activation of limbic structures and behavioural depression in response to peripheral administration of bacterial lipopolysaccharide

The European Journal of Neuroscience

Research report
Neural and behavioral responses to low-grade inflammation