Cold block of in vitro eyeblink reflexes: evidence supporting the use of hypothermia as an anesthetic in pond turtles

Abstract

Use of hypothermia as a means of anesthesia for amphibians and reptiles is prohibited by agencies that establish veterinary guidelines. This has recently been called into question by members of the scientific community based on reviews of published literature. Using pond turtles (Trachemys scripta elegans), hypothermia as a method for anesthesia to precede euthanasia by decapitation was assessed. Turtles were subjected to hypothermia using a cooling followed by freezing protocol. Body temperature measurements ranged between −1 to −2°C while core body temperature was −1°C. Ice crystal formation was never observed. A protective reflex to noxious stimuli, the eyeblink response, was recorded from in vitro brainstem preparations subjected to cold. At 5–6°C, reflex responses were suppressed, demonstrating minimal synaptic transmission in brain circuits above temperatures used for hypothermia induction. These and previous data indicate that a re-evaluation of the use of hypothermia as an anesthetic in amphibians and reptiles is warranted.