Differences between the Lewis and Sprague-Dawley rats in chronic inflammation induced norepinephrine sensitivity of cutaneous C-fiber nociceptors

We investigated whether there are any differences between the Lewis and Sprague-Dawley (SD) rats in chronic inflammation-induced norepinephrine (NE) sensitivity of nociceptors. Activities of C-fiber nociceptors innervating rat hairy hindpaw skin were recorded in an in vitro skin-nerve preparation. Sixty-five percent of C-fibers from inflamed Lewis rats were excited by NE (10 μM), against only 38% of C-fibers from inflamed SD rats. The average of the total impulses evoked in response to NE was also significantly higher in Lewis rats. The α2-adrenoceptor antagonist CH 38083 (10 μM) and yohimbine (10 μM) consistently blocked the NE-excitation of both strains. These results show that after chronic inflammation, C-fiber nociceptors of Lewis strain rats have a stronger sensitivity to NE, and that α2-adrenoceptors are predominately involved in the NE-sensitivity of inflamed rats in both strains.