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.