Contrasting effects of anesthetics in tadpole bioassays.

The median anesthetic concentrations (AC 50 values) in the bath solution for loss of righting reflex (RR) or nociceptor response (NR) were determined in larval Rana catesbeiana. The AC50 (NR)/AC50(RR) ratios were between 1.6 and 1.

Muscle weakness during tricaine anesthesia.

An isolated preparation of tadpole tail muscle was used to assess the peripheral effects of tricaine (3-aminobenzoic acid ethyl ester) at anesthetic concentrations and under physiological conditions. The drug effect on the electrically-evoked twitch was tested using short-pulse durations that elicited synaptically mediated effects or longer-duration pulses that stimulated the muscle directly. Tricaine reduced both types of response anesthetic and even subanesthetic concentrations.