An assessment of vascular pain using the flexor reflex in anesthetized rats

This study assessed the flexor reflex induced by intraarterial algogenic drugs ill anesthetized rats. The experiments were performed oil male Sprague Dawley rats weighing 290-350 g. The animals were anesthetized with urethane (1.3 g/kg i.p.) and an arterial cannula was inserted to the level of the bifurcation of the femoral artery. The magnitude. of the flexor reflex was examined by recording the electromyograph from the posterior biceps femoris/semitendinous muscles. Results showed that the flexor reflex evoked by intra-arterial injection of capsaicin (0.05-0.5 mug) was dosedependent. A similar reflex resulted from pinching the toe of the hindlimb. These responses were inhibited by morphine (5 mg/kg s.c.) cold restored with naloxone (1.5 mg/kg s.c.). Intraarterial preinjection of procaine (2%, 200 mul) and capsalzepine (20 mug), which is a selective vanilloid receptor antagonist. inhibited the capsaicin-evoked response, bill not that of pinching. These results indicate that the flexor reflex is a useful tool for assessing vascular pain in anesthetized animals. (C) Prous Science 2004. All rights reserved.