Bilateral lesions in the area of the nucleus locus coeruleus affect the development of hyperalgesia during carrageenan-induced inflammation.

We have compared the development of hyperalgesia following induction of unilateral inflammation between rats with bilateral lesions in the area of the locus coeruleus (LC) and rats with a sham operation. Unilateral inflammation was produced by the subcutaneous injection of carrageenan (6 mg in 0.15 ml saline). Prior to carrageenan injection, paw withdrawal latency (PWL) to thermal stimuli did not differ between the LC-lesioned and the sham-operated groups. After carrageenan injection, in the inflamed paw, the decreased PWLs of LC-lesioned rats were significantly shorter than those of sham-operated rats. This difference in PWL between the two groups was not observed in non-inflamed paws and in paws receiving an injection of saline. The result suggests that the area of the LC affects the development of hyperalgesia during peripheral inflammation.