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 (), 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 and -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 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.

Reference Intervals in Combined Veterinary Clinical Examinations of Male Black-Spotted Pond Frogs (Pelophylax nigromaculatus)

“…Amphibians and reptiles from temperate regions are acclimatized to freezing conditions over their life history, depending on the season [ 34 ]. Freezing anesthesia can greatly reduce the neural activity of amphibians, which can physically and chemically anesthetize animals without signs of pain [ 54 , 55 ]. Hence, we adopted the method of freezing anesthesia to anesthetize frogs in our study.…”

Anesthetic MS-222 eliminates nerve and muscle activity in frogs used for physiology teaching laboratories

“…Frogs were subsequently checked for responsiveness through a toe pinch and by touching the eye. Physiologically responsive frogs typically exhibit a corneal reflex when the eye is touched, and this behavior is dependent on reflexive circuits through the cranial nerves (17,20,23). A firm pinch of the toe to elicit a withdrawal reflex is a common test of nociceptive responses in amphibians (6,16,18,20,31,32).…”

“…There is growing concern from researchers and educators about the push to adhere to protocols that could ultimately restrict the use of ectothermic vertebrates (17,21,28). The most recent edition of the American Veterinary Medical Association (AVMA) Guidelines for the Euthanasia of Animals (1) proclaims that cooling of ectotherms like reptiles and amphibians is not an appropriate method of anesthesia or euthanasia.…”

“…However, as pointed out by an interdisciplinary panel, these recommendations are not evidence based and actually fly in the face of the scientific data (21). A body of compelling evidence indicates that cooling of ectotherms is a normal component of their life history, and that it significantly reduces neurological activity (17,21,28). There is growing concern that the directives provided in the AVMA guide are becoming de facto policy because the National Institutes of Health and other oversight organizations look to the AVMA as an authority for guiding the methods involving animals in research and teaching (17,21).…”

“…A body of compelling evidence indicates that cooling of ectotherms is a normal component of their life history, and that it significantly reduces neurological activity (17,21,28). There is growing concern that the directives provided in the AVMA guide are becoming de facto policy because the National Institutes of Health and other oversight organizations look to the AVMA as an authority for guiding the methods involving animals in research and teaching (17,21). Indeed, the most recent edition of the Guide for the Care and Use of Laboratory Animals states that, "unless a deviation is justified for scientific or medical reasons, methods should be consistent with the AVMA Guidelines on Euthanasia" (24).…”