A role for proinflammatory cytokines and fractalkine in analgesia, tolerance, and subsequent pain facilitation induced by chronic intrathecal morphine

Abstract

The present experiments examined the role of spinal proinflammatory cytokines [interleukin-1beta (IL-1)] and chemokines (fractalkine) in acute analgesia and in the development of analgesic tolerance, thermal hyperalgesia, and tactile allodynia in response to chronic intrathecal morphine. Chronic (5 d), but not acute (1 d), intrathecal morphine was associated with a rapid increase in proinflammatory cytokine protein and/or mRNA in dorsal spinal cord and lumbosacral CSF. To determine whether IL-1 release modulates the effects of morphine, intrathecal morphine was coadministered with intrathecal IL-1 receptor antagonist (IL-1ra). This regimen potentiated acute morphine analgesia and inhibited the development of hyperalgesia, allodynia, and analgesic tolerance. Similarly, intrathecal IL-1ra administered after the establishment of morphine tolerance reversed hyperalgesia and prevented the additional development of tolerance and allodynia. Fractalkine also appears to modulate the effects of intrathecal morphine because coadministration of morphine with intrathecal neutralizing antibody against the fractalkine receptor (CX3CR1) potentiated acute morphine analgesia and attenuated the development of tolerance, hyperalgesia, and allodynia. Fractalkine may be exerting these effects via IL-1 because fractalkine (CX3CL1) induced the release of IL-1 from acutely isolated dorsal spinal cord in vitro. Finally, gene therapy with an adenoviral vector encoding for the release of the anti-inflammatory cytokine IL-10 also potentiated acute morphine analgesia and attenuated the development of tolerance, hyperalgesia, and allodynia. Taken together, these results suggest that IL-1 and fractalkine are endogenous regulators of morphine analgesia and are involved in the increases in pain sensitivity that occur after chronic opiates.

Figure 1.

Chronic, but not acute, intrathecal infusion with morphine (Mor) induces the rapid release of IL-1 protein from the lumbar spinal cord determined by ELISA. Top, After five once-daily (chronic) intrathecal infusions of morphine (10 μg) or saline (Sal), there was an increase in IL-1 protein in lumbar spinal dorsal horn tissue 2 hr, but not 24 hr, after the last infusion of morphine. There was no change in IL-1 levels after a single ′infusion of morphine. Bottom, After five once-daily (chronic) intrathecal infusions of morphine (10 μg) or saline, there was an increase in IL-1 protein in lumbar spinal CSF 2 hr, but not 24 hr, after the last infusion of morphine. There was no change in IL-1 levels after a single infusion of morphine.

Figure 2.

Chronic, but not acute, intrathecal infusion with morphine (Mor) increases the expression of IL-6 and TNF-α mRNA in the lumbar spinal cord determined by RT-PCR. Top, There were no significant differences in relative levels of IL-1 mRNA expression after a single or five once-daily (chronic) infusions of morphine (10 μg) or saline (Sal) in lumbar spinal dorsal horn tissue. Middle, After five once-daily (chronic) intrathecal infusions of morphine (10 μg) or saline, there was an increase in IL-6 mRNA expression in lumbar spinal dorsal horn tissue 2 hr, but not 24 hr, after the last infusion of morphine. There was no change in IL-6 mRNA expression after a single infusion of morphine. Bottom, After five once-daily (chronic) intrathecal infusions of morphine (10 μg) or saline, there was an increase in TNF mRNA expression in lumbar spinal dorsal horn tissue 2 hr, but not 24 hr, after the last infusion of morphine. There was no significant change in TNF mRNA expression after a single infusion of morphine.

Figure 3.

Coadministration of an IL-1ra with intrathecal morphine potentiates morphine analgesia. Top, The analgesic effect of intrathecal morphine (10 μg) was reduced by five once-daily infusions of morphine in the tail flick withdrawal reflex from an infrared light source. Coadministration of IL-1ra with intrathecal morphine potentiates acute morphine analgesia on day 1 and attenuates the development of analgesic tolerance. Bottom, Previous treatment with IL-1ra reduced the expression of tolerance in rats previously given five once-daily infusions of morphine. A probe trial for analgesia was conducted on day 6 to determine the extent of tolerance in the absence of IL-1ra. All subjects received an intrathecal infusion of morphine (5 μg). Veh, Vehicle; Sal, saline; Mor, morphine.

Figure 4.

Coadministration of an IL-1ra with an intrathecal infusion of morphine attenuates the development of exaggerated pain sensitivity after morphine. Top, Animals given five once-daily infusions of morphine (10 μg) developed thermal hyperalgesia in the tail flick test using an infrared light source when tested 24 hr after the last infusion of morphine. Coadministration of IL-1ra (100 μg) reduced the hyperalgesic effect of morphine. Bottom, Animals given five once-daily infusions of morphine (10 μg) developed tactile allodynia in the von Frey test when tested 24 hr after the last infusion of morphine. Coadministration of IL-1ra (100 μg) reduced the allodynic effect of morphine.

Figure 5.

Coadministration of an IL-1ra with intrathecal morphine in morphine-tolerantrats attenuates the additional development of analgesic tolerance. Top, Rats received five once-daily intrathecal infusions of morphine (Mor; 10 μg) or saline to induce analgesic tolerance in the tail flick test. On days 6-9, the rats were coadministered IL-1ra (100 μg) or its vehicle (Veh) with morphine (10 μg) or saline (Sal). Treatment with IL-1ra attenuated the additional development of analgesic tolerance. Bottom, A probe trial for analgesia was conducted on day 10 to determine the extent of tolerance in the absence of IL-1ra in which all subjects received an intrathecal infusion of morphine (5 μg). Treatment with IL-1ra across days 6-9 increased the analgesic effect of morphine in morphine-treated rats.

Figure 6.

Coadministration of an IL-1ra with an intrathecal infusion of morphine in rats previously made tolerant to morphine attenuates the development of exaggerated pain sensitivity after morphine. Top, Rats received five once-daily intrathecal infusions of morphine (10 μg) or saline to induce analgesic tolerance in the tail flick test. On days 6-9, the rats were coadministered IL-1ra (100 μg) or its vehicle with morphine (10 μg) or saline. Treatment with IL-1ra attenuated the development of thermal hyperalgesia in the tail flick test when tested on day 10, 24 hr after the last drug infusion. Bottom, Treatment with IL-1ra on days 6-9 also attenuated the development of tactile allodynia in the von Frey test when tested on day 10, 24 hr after the last drug infusion.

Figure 7.

Coadministration of a fractalkine receptor (CX3CR1) neutralizing antibody (anti-FKR) with intrathecal morphine potentiates morphine analgesia. Rats received an intrathecal infusion of anti-FKR (10 μg) or its vehicle on day 0. On days 1-5, rats received an intrathecal infusion of anti-FKR or its vehicle and morphine (10 μg) or saline. Left, The analgesic effect of intrathecal morphine was reduced by five once-daily infusions of morphine in the tail flick withdrawal reflex from an infrared light source. Coadministration of anti-FKR with intrathecal morphine potentiates acute morphine analgesia on day 1 and attenuates the development of analgesic tolerance apparent on day 5. Middle, Five once-daily infusions of morphine increased pain sensitivity in the tail flick test. This thermal hyperalgesia was reduced by coadministration of anti-FKR with intrathecal morphine when tested on day 6, 24 hr after the last drug infusion. Right, Five once-daily infusions of morphine increased tactile sensitivity in the von Frey test. This tactile allodynia was reduced by coadministration of anti-FKR with intrathecal morphine when tested on day 6, 24 hr after the last drug infusion.

Figure 8.

Lumbosacral intrathecal injection with an adenovirus expressing interleukin-10 (ADIL-10) potentiates intrathecal morphine analgesia. Rats received an intrathecal infusion with adenoviral vectors expressing IL-10 (5 μg) or β-galactosidase (Control) 5 d before the start of testing. Rats then received five once-daily infusions of morphine (10 μg). Left, The analgesic effect of intrathecal morphine was reduced by five once-daily infusions of morphine in the tail flick withdrawal reflex from an infrared light source. Treatment with ADIL-10 with intrathecal morphine potentiated acute morphine analgesia on day 1 and attenuated the development of analgesic tolerance apparent on day 5. Middle, Five once-daily infusions of morphine increased pain sensitivity in the tail flick test. Prevoius treatment with ADIL-10 reduced this thermal hyperalgesia. Right, Five once-daily infusions of morphine increased tactile sensitivity in the von Frey test. This tactile allodynia was reduced by previous treatment with ADIL-10.