The Formalin Test in African Toad (Bufo regularis)- a Novel Pain Model in Amphibians

Abstract: The formalin test was evaluated in African toad (Bufo regularis) with 37 % formaldehyde (100 % formalin) using a multi-dimensional motor activity scoring. The responses were biphasic like those obtained in rodents but with longer first phase, longer interval and longer second phase. Acetylsalicylic acid (70 mg kg) reduced significantly responses in both phases while indomethacin only reduced the second1 phase responses. The first phase is likely due to direct activation of nociceptors by formalin while the second phase suggests the involvement of inflammation. These results are similar to what has been observed in rodents although the physiological mechanisms may not be exactly the same. It is suggested that formalin test in toads is a valid experimental pain model in amphibians for the evaluation of longer-acting analgesics. Key words: Formalin African toad Bufo regualaris Acetylsalicylic acid indomethacin analgesic INTRODUCTION adopted in its understanding. This fact is further A number of behavioural methods have been the time course and pharmacologic influences are developed in order to study nociception in animals. similar, it is doubtful whether the time course and thus Several of these tests: the tail flick test, the flinch-jump the physiological mechanisms in other species are test, the pinch test and the hot plate test measure the similar to what obtains in rodents [11]