Anesthesia of the Leopard Frog, Rana pipiens: A Comparative Study between four Different Agents

Abstract

OBJECTIVES: To compare the anesthetic effects of tricaine methanesulfonate, clove oil, Orajel® and Emla® on leopard frogs, Rana pipiens. STUDY DESIGN: Four groups of 12 fully metamorphosed frogs, weighing from 4 to 13 g were used for this study. Frogs from each group were topically exposed for five minutes to one of the following treatment: a buffered solution of 1 g/L of tricaine methanesulfonate, a suspension of clove oil (255 mg/L of eugenol), 11.5 mg of benzocaine (Orajel® cream) and 60 mg of a 1:1 mixture of lidocaine:prilocaine (Emla® cream). Levels of anesthesia were assessed based on the loss of righting reflex, corneal reflex, superficial pain sensation and deep pain sensation. Variations of the cardiac and respiratory rates were monitored throughout the anesthetic procedure. Chi-square exact test, post-hoc test, tukey post-hoc test and linear model were used to compare the results obtained with the different agents. CONCLUSIONS: Tricaine methanesulfonate was the most effective agent tested inducing surgical plane of anesthesia in all the frogs. Exposure to clove oil and Orajel® cream induced immobility in 96.7% and 66.7% of the frogs, respectively, but these two compounds failed to provide adequate analgesia for surgical stimuli in approximately half of the frogs. Consequently, at the dosages used in the current study, these compounds are not recommended for procedures involving painful stimuli. Exposure to Emla® cream was associated with a high mortality rate (42%) and should not be used for anesthesia of frogs. Several time parameters measured were affected by the size of the individual frogs; the anesthetic effects being usually greater in smaller frogs. The absence of corneal reflex was usually predictive of the loss of superficial pain sensation. A marked respiratory depression, frequently leading to prolonged apnea, was induced with all four agents tested.