An IL-1 receptor antagonist blocks a morphine-induced attenuation of locomotor recovery after spinal cord injury

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Abstract

Morphine is one of the most commonly prescribed medications for the treatment of chronic pain after a spinal cord injury (SCI). Despite widespread use, however, little is known about the secondary consequences of morphine use after SCI. Unfortunately, our previous studies show that administration of a single dose of morphine, in the acute phase of a moderate spinal contusion injury, significantly attenuates locomotor function, reduces weight gain, and produces symptoms of paradoxical pain (Hook et al., 2009). The current study focused on the cellular mechanisms that mediate these effects. Based on data from other models, we hypothesized that pro-inflammatory cytokines might play a role in the morphine-induced attenuation of function. Experiment 1 confirmed that systemic morphine (20 mg/kg) administered one day after a contusion injury significantly increased expression levels of spinal IL-1β 24 h later. Experiment 2 extended these findings, demonstrating that a single dose of morphine (90 μg, i.t.) applied directly onto the spinal cord increased expression levels of spinal IL-1β at both 30 min and 24 h after administration. Experiment 3 showed that administration of an interleukin-1 receptor antagonist (IL-1ra, i.t.) prior to intrathecal morphine (90 μg), blocked the adverse effects of morphine on locomotor recovery. Further, pre-treatment with 3 μg IL-1ra prevented the increased expression of at-level neuropathic pain symptoms that was observed 28 days later in the group treated with morphine-alone. However, the IL-1ra also had adverse effects that were independent of morphine. Treatment with the IL-1ra alone undermined recovery of locomotor function, potentiated weight loss and significantly increased tissue loss at the injury site. Overall, these data suggest that morphine disrupts a critical balance in concentrations of pro-inflammatory cytokines in the spinal cord, and this undermines recovery of function.

Research highlights

► Morphine undermines locomotor recovery and increases pain symptoms after SCI. ► IL-1ra pre-treatment blocks the morphine-induced attenuation of locomotor recovery. ► The IL-1ra administered alone attenuated locomotor recovery after spinal injury. ► IL-1ra treatment blocks the development of at-level pain symptoms after SCI. ► IL-1ra pre-treatment reduces weight gain after SCI.

Introduction

Our previous studies suggest that morphine, administered in the acute phase of a spinal contusion injury, significantly undermines recovery of function and increases the expression of paradoxical pain symptoms in the chronic phase of injury (Hook et al., 2007, Hook et al., 2009). Despite producing analgesia, a single dose of systemic morphine administered one day after a moderate contusion injury, led to allodynic responses to innocuous sensory stimuli (three weeks later), decreased sensory function, decreased weight gain, and increased lesion size when compared with vehicle-treated controls (Hook et al., 2007). Intrathecal morphine significantly attenuated the recovery of locomotor function, decreased weight gain, increased the incidence of autophagia, and increased lesion size rostral to the injury site (Hook et al., 2009). These data suggest that caution is warranted when administering morphine in the acute phase of a spinal cord injury (SCI). For SCI patients faced with a lifetime of intractable pain, however, simply removing morphine as a potential analgesic is not an option. It is essential that we further our understanding of the consequences of, and molecular mechanisms engaged by, commonly used opiate analgesics.

Recent studies have implicated the immune system in the development of the ‘paradoxical’ pain observed with morphine administration (Watkins et al., 2005, Watkins et al., 2007, Scholz and Woolf, 2007). These studies have shown that repeated morphine administration activated microglia and astrocytes (Song and Zhao, 2001, Cui et al., 2006, Raghavendra et al., 2002, Tai et al., 2006), and increased TNFα, IL-1β and IL-6 expression in the spinal cord (Johnston et al., 2004, Raghavendra et al., 2002, Tai et al., 2006). These pro-inflammatory cytokines block the analgesic effects of opioids (Gul et al., 2000, Szabo et al., 2002), and have been linked to the development of paradoxical pain symptoms. Indeed, at a cellular level, IL-1β has been shown to facilitate substance-P release from primary afferent neurons in the spinal dorsal horn (Inoue et al., 1999), increase tyrosine phosphorylation of the NMDA receptor NR2B subunit (Viviani et al., 2003), increase surface expression of AMPA receptors (Stellwagen et al., 2005), and has been linked to inhibition of glutamate transporters such as GLT-1 and GLAST (Tai et al., 2006, Prow and Irani, 2008). Subsequent increases in neuroexcitability, with the potentiation of the glutamate signal, underlies the development of central sensitization, a mechanism that results in increased pain reactivity and may exacerbate the secondary neuronal death seen after spinal injury. Also, the pro-inflammatory cytokines, TNFα and IL-1β, activate NF-κB, which is the transcriptional regulator of the synthesis of the inducible form of nitric oxide synthase (iNOS) (Conti et al., 2007). Increased iNOS activity elevates basal nitric oxide (NO) levels, which may also exacerbate the secondary neuronal death seen after spinal injury (Conti et al., 2007). Clearly, the changes in pain reactivity, increased lesion size, and the decreased recovery of function observed with morphine administration may be due to elevations of pro-inflammatory cytokine levels.

The effects of morphine on the immune system are particularly relevant in a spinal contusion injury, which is characterized by inflammation. Pro-inflammatory cytokine levels are significantly upregulated 1, 3, and 6 h after a contusion injury, returning to background levels after 1–3 days (Yang et al., 2004, Yang et al., 2005, Wang et al., 2005, Pineau and Lacroix, 2007). In the early stages of injury, pro-inflammatory cytokines appear to have beneficial effects as they are involved in the regulation of leukocyte recruitment and microglial activation. However, they have also been linked to cytotoxic effects (Merrill and Benveniste, 1996, Gruol and Nelson, 1997, Knoblach et al., 1999, Nesic et al., 2001). Indeed, Yang et al. (2005) suggest that there is a concentration-dependent relationship, and critical balance, between the beneficial and toxic effects of pro-inflammatory cytokines. As morphine increases the expression of pro-inflammatory cytokines, we hypothesize that superimposing this analgesic on the vulnerable contusion site may push the injured system past an adaptive inflammatory response to cytotoxic levels thereby increasing the expression of paradoxical pain symptoms and cell death. To test this hypothesis, the initial experiments confirmed that acute morphine administration increased pro-inflammatory cytokine levels at the site of injury. This effect was observed with both systemic (Experiment 1) and intrathecal (Experiment 2) morphine administration. Experiment 3 then examined whether co-administration of an IL-1 receptor antagonist (IL-1ra) and morphine would block the morphine-induced attenuation of recovery of function. In Experiment 3, both morphine and the IL-1ra were applied directly onto the spinal cord, thereby focusing the loci of changes on the vulnerable contusion site. We found that the IL-1ra did prevent the effects of morphine on recovery of locomotor function and blocked the development of at-level neuropathic symptoms. However, subjects treated with the IL-1ra alone also displayed a dose-dependent attenuation of weight gain after injury, and increased tissue loss across the extent of the lesion.

Section snippets

Subjects

The subjects were male Sprague–Dawley rats obtained from Harlan (Houston, TX). They were approximately 90–110 days old (300–350 g) and were individually housed in Plexiglas bins [45.7 (length) × 23.5 (width) × 20.3 (height) cm] with food and water continuously available. To facilitate access to the food and water, extra bedding was added to the bins after surgery and long mouse sipper tubes were used so that the rats could reach the water without rearing. Subjects were weighed on the same days that

Experiment 1

Day 1 BBB scores were indicative of a moderate contusion injury: prior to morphine treatment, subjects assigned to the morphine and saline treatment groups, respectively, displayed mean (±SEM) converted BBB scores of 2.0 ± 0.56 and 2.75 ± 0.58 (equivalent to untransformed BBB scores of 2.69 ± 0.76 and 3.56 ± 0.89, respectively).

There was a significant main effect of systemic morphine treatment on levels of IL-1β in spinal tissue taken from the injury site 24 h after drug treatment (F(1, 14) = 23.50, p < 

Discussion

As found in our previous studies, intrathecal morphine applied in the acute phase of SCI significantly undermined recovery of locomotor function, and increased the expression of symptoms of paradoxical pain in the chronic phase of injury. These adverse effects of morphine appear to depend on activation of the IL-1 receptor. Expression levels of IL-1β in the injured spinal cord were significantly elevated 24 h after systemic morphine administration compared with vehicle controls. Similarly,

Conflicts of interest statement

All authors declare that there are no conflicts of interest.

Acknowledgments

This study was supported by NS041548 and HD058412 to James Grau and Michelle Hook, and Mission Connect, a project of the TIRR foundation. A portion of the data from this study has been previously presented in abstract form.

References (56)

  • S. Liu et al.

    Regulation of interleukin-1beta by the interleukin-1 receptor antagonist in the glutamate-injured spinal cord: endogenous neuroprotection

    Brain Res.

    (2008)
  • J.E. Merrill et al.

    Cytokines in inflammatory brain lesions: helpful and harmful

    Trends Neurosci.

    (1996)
  • M. Nakamura et al.

    Differences in cytokine gene expression profile between acute and secondary injury in adult rat spinal cord

    Exp. Neurol.

    (2003)
  • A.J. Reeve et al.

    Intrathecally administered endotoxin or cytokines produce allodynia, hyperalgesia and changes in spinal cord neuronal responses to nociceptive stimuli in the rat

    Eur. J. Pain

    (2000)
  • Y. Shavit et al.

    Interleukin-1 antagonizes morphine analgesia and underlies morphine tolerance

    Pain

    (2005)
  • P. Song et al.

    The involvement of glial cells in the development of morphine tolerance

    Neurosci. Res.

    (2001)
  • Y.H. Tai et al.

    Amitriptyline suppresses neuroinflammation and up-regulates glutamate transporters in morphine-tolerant rats

    Pain

    (2006)
  • L.R. Watkins et al.

    Glia: novel counter-regulators of opioid analgesia

    Trends Neurosci.

    (2005)
  • L.R. Watkins et al.

    Glia as the “bad guys”: implications for improving clinical pain control and the clinical utility of opioids

    Brain Behav. Immun.

    (2007)
  • L. Yang et al.

    Severity-dependent expression of pro-inflammatory cytokines in traumatic spinal cord injury in the rat

    J. Clin. Neurosci.

    (2005)
  • R.X. Zhang et al.

    IL-1ra alleviates inflammatory hyperalgesia through preventing phosphorylation of NMDA receptor NR-1 subunit in rats

    Pain

    (2008)
  • D.M. Basso et al.

    A sensitive and reliable locomotor rating scale for open field testing in rats

    J. Neurotrauma

    (1995)
  • M.S. Beattie

    Anatomic and behavioral outcome after spinal cord injury produced by a displacement controlled impact device

    J. Neurotrauma

    (1992)
  • D.L. Behrmann et al.

    Spinal cord injury produced by consistent mechanical displacement of the cord in rats: behavioral and histologic analysis

    J. Neurotrauma

    (1992)
  • M.D. Christensen et al.

    Chronic central pain after spinal cord injury

    J. Neurotrauma

    (1997)
  • S. Constantini et al.

    The effects of methylprednisolone and the ganglioside GM1 on acute spinal cord injury in rats

    J. Neurosurg.

    (1994)
  • E.D. Crown et al.

    Shock-induced hyperalgesia: III. Role of the bed nucleus of the stria terminalis and amygdaloid nuclei

    Behav. Neurosci.

    (2000)
  • A.R. Ferguson et al.

    A simple post hoc transformation that improves the metric properties of the BBB scale for rats with moderate to severe spinal cord injury

    J. Neurotrauma

    (2004)
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