Central effects of tumor factor alfa and interleukin-1a on nociceptive thresholds and spontaneous locomotor activity

To extend the knowledge on the central effects of cytokines, we studied the effects of tumor necrosis factor α and interleukin-1α on nociceptive thresholds and spontaneous locomotor activity in rats. After central administration, both tumor necrosis factor α and interleukin-1α significantly (P<0.001) increase the nociceptive thresholds as measured by the hot-plate test. Tumor necrosis factor α, but not interleukin-1α decreases spontaneous locomotor activity evaluated by the Animex test. The increase in nociceptive thresholds induced by tumor necrosis factor α or interleukin-1α is not affected by the opiate receptor antagonist naloxone, or antisera against the endogenous opioids β-endorphin, met-enkephalin or dynorphin. The analgesic effect of tumor necrosis factor α is completely antagonized by anti-IL-1 antibodies. Moreover, the cyclooxygenase inhibitor indomethacin does not antagonize the increase of nociceptive thresholds induced by either cytokine.