Thermal hyperalgesic effects induced by intracerebroventricular injection of interleukin-1beta in rats

The present study was to investigate the effects of intracerebroventricular (i.c.v.) injection of interleukin-1beta (IL-1beta) on thermal nociception in SD rats. The rats were divided into control and drug-administration groups. The animals of control group were given vehicle solution via i.c.v. injection. The animals of drug-administered groups were given IL-1beta at different doses (5, 50 and 500 pg/kg b.w.) via i.c.v. injection. IL-1 receptor antagonist (IL-1ra, 50 ng/kg) was injected 20 min before injection of IL-1beta or vehicle solution. The nociceptive threshold, which was represented as paw withdrawal latency (PWL), to a noxious thermal stimulation was measured using an analgesiameter. I.c.v. injection of IL-1beta dose-dependently shortened the PWL. At the dose of 500 pg/kg, the shortening of the PWL occurred at 20 min, reaching a peak within 40 min, lasted 100 min after injection, then gradually returned to the baseline level. Pretreatment with IL-1ra completely blocked the effects of IL-1beta-induced shortening in PWL. The results obtained suggest that IL-1beta may induce hyperalgesia in rats through binding to IL-1 receptors in the brain.