Cutaneous hyperalgesia induced by peripheral injection of interleukin-1β in the rat

The contribution of the activity of afferent fiber filaments to pain and hyperalgesia after administration of a plantar injection of interleukin-1β (IL-1β) to the hind-paw skin was investigated by recording action potentials of the rat dorsal root in response to mechanical and thermal stimuli. Touch stimuli were delivered by stroking with a cotton-tipped applicator and thermal stimulation was applied by cooling or heating of the skin. After the administration of IL-1β (100 pg-1 μg), response to touch, cold, and heat stimulation increased to 143%, 200%, and 392%, respectively, of control values on average. IL-1β induced transient spontaneous discharge in 50% of experiments. The effects of IL-1β were apparent within 1 min. To examine responses to pressure stimulation, an area of 1 mm 2 of the hind-paw skin was pressed by a mechanical stimulator. IL-1β (0.1 pg-200 ng) decreased the threshold value to 58% of the control pressure required for firing. IL-1β also increased responses to various levels of pressure (range: 1–20 g/mm 2). These data suggest that IL-1β may play an important role in cutaneous hyperalgesia by activating polymodal receptors to mechanical and thermal stimulation.