EFFECTS OF FORMALIN-INDUCED PAIN ON EXPLORATORY-BEHAVIOR IN RABBITS

WE have used formalin to assess the long-term behavioural and hormonal effects of persistent pain in rabbits. Behaviour has been recorded ov er 10 min sessions both before and after 10 min, 4 and 24 hours after injection of formalin. A low dose of formalin (0.1 ml at 5%) elicited licking of the injected paw which lasted only a few minutes. Explorato ry behaviour was greater than in the control (sham-injected) animals i n all post-injection sessions. Following a larger dose of formalin (0. 5 ml at 8%) licking occurred in all post-injection sessions, while exp loration was lower than the controls only immediately after injection. Twenty-four hours after the formalin injection, testosterone levels w ere unaffected. Corticosterone levels increased over the course of the experiment but this increase was equal for the experimental and the c ontrol groups. Results suggest that different pain intensities and dur ations have opposite effects on exploratory behaviour in rabbits.