Pain Management for Gastrointestinal Conditions in Exotic Animals

Gastrointestinal (GI) disorders are very common in exotic animals, such as reptiles, birds, mammals, and can be extremely painful. This review aims to provide the reader with a better understanding of the different pain mechanisms and manifestations across orders and species in order to provide the most updated information on pain recognition and management for GI conditions in exotic animals.

Rapid stimulation of protein synthesis in digesting snakes: Unveiling a novel gut-pancreas-muscle axis

AIM

Snakes exhibit remarkable physiological shifts when their large meals induce robust postprandial growth after prolonged fasting. To understand the regulatory mechanisms underlying this rapid metabolic transition, we examined the regulation of protein synthesis in pythons, focusing on processes driving early postprandial tissue remodeling and growth.

METHODS

Using the SUnSET method with puromycin labeling, we measured in vivo protein synthesis in fasting and digesting snakes at multiple post-feeding intervals. Pyloric ligation, pancreatectomy, and plasma transfusions were performed to explore the roles of gastrointestinal luminal signaling and pancreatic function across key tissues.

RESULTS

We observed profound and early stimulation of protein synthesis in gastrointestinal tissues and skeletal muscle already 3 h after ingestion, before any measurable rise in plasma amino acids from the meal. The gastrointestinal stimulation appears to be driven by luminal factors, while the stimulation of skeletal muscle protein synthesis is humoral with pancreatic insulin release as an integral mediator. The pre-absorptive anabolic activity is supported by the release of amino acids from the breakdown of endogenous proteins.

CONCLUSIONS

Our findings suggest that snakes initiate protein synthesis via distinct, tissue-specific pathways preceding nutrient absorption. This "pay before pumping" model shows how early protein synthesis prepares the digestive and muscular systems for later nutrient assimilation and growth. This intricate humoral regulation, involving a gut-pancreas-muscle axis, governs postprandial protein synthesis in snakes and provides insights into fundamental mechanisms driving metabolic adaptations and broader hyperplastic and hypertrophic responses.

Impact of procedural handling on the physiological effects of alfaxalone anaesthesia in the ball python (Python regius)

To describe the cardiovascular changes following intramuscular (handled) and intravascular (undisturbed, via intraarterial catheter) alfaxalone administration, we studied 20 healthy ball pythons (Python regius) in a randomised, prospective study. The pythons were instrumented with occlusive arterial catheters to facilitate undisturbed, continuous monitoring of heart rate and blood pressure. Six pythons were administered intramuscular (IM) saline, followed by 20 mg/kg IM alfaxalone, and were manually restrained for both injections. Six pythons received intraarterial (IA) saline, followed by 10 mg/kg IA alfaxalone, and remained undisturbed for both injections. Arterial blood samples were taken at 0, 12 and 60 min post-injection, and heart rate and blood pressure were recorded for 60 min. The remaining eight snakes received 20 mg/kg IM or 10 mg/kg IA alfaxalone (n = 4 per treatment) and were not handled for intubation 10 min post-injection, to examine the effects of handling during anaesthesia. IM administration of 20 mg/kg alfaxalone or an equivalent volume of saline elicited a profound tachycardia and hypertension, which recovered to resting values after 20 min. However, when 10 mg/kg alfaxalone or saline were injected IA, mild hypotension and a lower magnitude tachycardia occurred. Arterial PCO2 and PO2, pH and lactate concentrations did not change following IA alfaxalone, but an acidosis was observed during IM alfaxalone anaesthesia. There were no significant changes in plasma catecholamines and corticosterone among treatments. Handling for injection and during anaesthesia associated with intubation significantly affects cardiovascular parameters, whereas alfaxalone per se only elicits minor changes in cardiovascular physiology.

The pancreas does not contribute to the non-adrenergic-non-cholinergic stimulation of heart rate in digesting pythons

Vertebrates elevate heart rate when metabolism increases during digestion. Part of this tachycardia is due to a non-adrenergic-non-cholinergic (NANC) stimulation of the cardiac pacemaker, and it has been suggested these NANC factors are circulating hormones that are released from either gastrointestinal or endocrine glands. The NANC stimulation is particularly pronounced in species with large metabolic responses to digestion, such as reptiles. To investigate the possibility that the pancreas may release hormones that exert positive chronotropic effects on the digesting Burmese python heart, a species with very large postprandial changes in heart rate and oxygen uptake, we evaluate how pancreatectomy affects postprandial heart rate before and after autonomic blockade of the muscarinic and the beta-adrenergic receptors. We also measured the rates of oxygen consumption and evaluated the short-term control of the heart using the spectral analysis of heart rate variability and the baroreflex sequence method. Digestion caused the ubiquitous tachycardia, but the intrinsic heart rate (revealed after the combination of atropine and propranolol) was not affected by pancreatectomy and therefore hormones, such as glucagon and insulin, do not appear to contribute to the regulation of heart rate during digestion in Burmese pythons.

SERUM FENTANYL CONCENTRATIONS AND BEHAVIOR ASSOCIATED WITH TRANSDERMAL FENTANYL APPLICATION ON HEALTHY CORN SNAKES (PANTHEROPHIS GUTTATUS)

Snakes are common household pets and frequently managed in zoos. Geriatric snakes commonly develop osteoarthritis, leading to a declining quality of life that often results in euthanasia. Anecdotally, the application of transdermal fentanyl patches (TFP) appears to contribute to clinical improvement, including increased activity level, in osteoarthritic snakes presumed to be in pain. This study evaluated serum fentanyl concentrations over time and the effects of TFP on the normal behavior of healthy, captive, adult corn snakes (Pantherophis guttatus) using constant video monitoring. Serum fentanyl concentrations were evaluated over 4 wk during 12.5 µg/h TFP application, and the results demonstrated long-lasting (>4 wk) serum concentrations that were consistent with analgesic efficacy in mammalian species during TFP application. At 4 wk of TFP application, mean serum fentanyl concentrations were 11.5 ± 5.5 ng/ml. Snakes were videotaped for 1 wk prior to and 2 wk after 12.5 µg/h TFP application, and behavior was evaluated by an ethogram. Behavioral changes associated with TFP application included decreased mean time spent active, decreased mean number of climbs, and decreased mean number of water visits; feeding behavior was unchanged. Overall, these results suggest that TFP application may provide safe, clinically effective analgesia in healthy corn snakes for at least 4 wk without inducing deleterious side effects, and may therefore be appropriate analgesia for management of osteoarthritic snakes.

Treatment of Pain in Reptiles

This chapter provides an overview of our current understanding of clinical analgesic use in reptiles. Currently, μ-opioid agonist drugs are the standard of care for analgesia in reptiles. Reptile pain is no longer considered a necessary part of recovery to keep the reptile from becoming active too early. Rather, treating pain allows for the reptile to begin normalizing their behavior. This recognition of pain and analgesia certainly benefits our reptile patients and greatly improves reptile welfare, but it also benefits our students and house officers, who will carry the torch and continue to demand excellence in reptile medicine.

A Critical Review on the Pharmacodynamics and Pharmacokinetics of Non-steroidal Anti-inflammatory Drugs and Opioid Drugs Used in Reptiles

Non-steroidal anti-inflammatory drugs (NSAIDs) and opioids are analgesics used for moderate to severe pain in many animals, including reptiles. However, reptilian dosing regimens are often extrapolated from other animal species. This is not ideal as inter- and intra-species variability in physiology may result in varied drug disposition. Therefore, this critical review aims to collate data from pharmacological studies of selected NSAIDs and opioids performed in reptile and provide an analysis and discussion on the existing pharmacodynamic knowledge and pharmacokinetic data of NSAIDs and opioids use in reptiles. Additionally, key pharmacokinetic trends that may aid dosing of NSAIDs and opioids in reptiles will also be highlighted. Most of the existing reports of NSAID used in reptiles did not observe any adverse effects directly associated to the respective NSAID used, with meloxicam being the most well-studied. Despite the current absence of analgesic efficacy studies for NSAIDs in reptiles, most reports observed behavioural improvements in reptiles after NSAID treatment. Fentanyl and morphine were studied in the greatest number of reptile species with analgesic effects observed with the doses used, while adverse effects such as sedation were observed most with butorphanol use. While pharmacokinetic trends were drug- and species-specific, it was observed that clearance (CL) of drugs tended to be higher in squamates compared to chelonians. The half-life (t_1/2) of meloxicam also appeared to be longer when dosed orally compared to other routes of drug administration. This could have been due to absorption-rate limited disposition. Although current data provided beneficial information, there is an urgent need for future research on NSAID and opioid pharmacology to ensure the safe and effective use of opioids in reptiles.

COMPLETE UNILATERAL MAXILLECTOMY IN A COHORT OF FIVE COLOMBIAN BOAS (BOA IMPERATOR)

Five unrelated adult Colombian boas (Boa imperator) presented with a 1- to 3-mon history of unilateral rostral swelling of the maxilla associated with a chronic rubbing against the enclosure's walls. Moderate to severe gingival inflammation and ulceration of the labial mucosa were present at the level of the swelling with tenderness to the touch. Radiography revealed osteolytic or proliferative lesions of the maxillary bone. Chronic maxillary osteomyelitis was diagnosed. Unilateral maxillectomy was performed on each animal under general anesthesia. Local anesthesia was also achieved by infiltrating lidocaine along the medial and lateral aspect of the maxillary gingiva and at the level of the maxillo-ectopterygoid joint. Using a lateral gingival approach, the maxillo-prefrontal, maxillary-palatine, and maxillo-ectopterygoid attachments were transected, and the maxillary bone removed. Histologic examination revealed pyogranulomatous stomatitis and osteomyelitis in all snakes, and presence of intralesional bacteria (n = 3 snakes). Gram-negative bacteria (Chryseobacterium indologenes and Proteus mirabilis) were cultured from the resected tissue of two snakes. One snake suffered from wound dehiscence 5 d postoperatively. All snakes were fed 15 d postoperatively and ingested dead mice without apparent difficulties. One snake was examined 2 mon and 1 yr after surgery, with no evidence of soft tissue or osseous infection and only minor facial scaring; all other snakes were lost to follow-up 15 d after surgery. Unilateral maxillectomy was performed in a cohort of five Colombian boas suffering from maxillary osteomyelitis. This surgical technique should be considered as an alternative to medical treatment in boid snakes.

Pain and Pain Management in Sea Turtle and Herpetological Medicine: State of the Art

Simple Summary

Rescue and rehabilitative medicine of sea turtles must deal with several circumstances that would be certainly considered painful in other species (trauma, situations that require surgery); thus, it would be natural to consider the use of analgesic drugs to manage the pain and avoid its deleterious systemic effects to guarantee a rapid recovery and release. However, in these animals (as well as in reptiles in general), many obstacles stand in the way of the application of safe and effective therapeutic protocols. It has been demonstrated that, anatomically and physiologically, turtles and reptiles in general must be considered able to experience pain in its definition of an “unpleasant sensory and emotional experience”. Unfortunately, specific studies concerning sea turtles and reptiles on pain assessment, safety, and clinical efficacy of analgesic drugs currently in use (mostly opioids and non-steroidal anti-inflammatory drugs—NSAIDs) are scarce and fragmentary and suffer from some basic gaps or methodological bias that prevent a correct interpretation of the results. At present, the general understanding of the physiology of reptiles’ pain and the possibility of its reasonable treatment is still in its infancy, considering the enormous amount of information still needed, and the use of analgesic drugs is still anecdotal or dangerously inferred from other species.

Abstract

In sea turtle rescue and rehabilitative medicine, many of the casualties suffer from occurrences that would be considered painful in other species; therefore, the use of analgesic drugs should be ethically mandatory to manage the pain and avoid its deleterious systemic effects to guarantee a rapid recovery and release. Nonetheless, pain assessment and management are particularly challenging in reptilians and chelonians. The available scientific literature demonstrates that, anatomically, biochemically, and physiologically, the central nervous system of reptiles and chelonians is to be considered functionally comparable to that of mammals albeit less sophisticated; therefore, reptiles can experience not only nociception but also “pain” in its definition of an unpleasant sensory and emotional experience. Hence, despite the necessity of appropriate pain management plans, the available literature on pain assessment and clinical efficacy of analgesic drugs currently in use (prevalently opioids and NSAIDs) is fragmented and suffers from some basic gaps or methodological bias that prevent a correct interpretation of the results. At present, the general understanding of the physiology of reptiles’ pain and the possibility of its reasonable treatment is still in its infancy, considering the enormous amount of information still needed, and the use of analgesic drugs is still anecdotal or dangerously inferred from other species.

Multi-Injection Pharmacokinetics of Meloxicam in Kemp's Ridley (Lepidochelys kempii) and Green (Chelonia mydas) Sea Turtles after Subcutaneous Administration

The objective of this study was to determine the pharmacokinetics and safety of multiple injections of meloxicam (MLX) administered subcutaneously (SQ) in Kemp's ridley (Lepidochelys kempii) and green (Chelonia mydas) sea turtles. Based on results from a previously published single-injection study, a multiple-injection regimen was derived for the Kemp's ridleys, which consisted of administering MLX at a dose of 1 mg/kg SQ every 12 h for 5 days, and for green turtles at a dose of 1 mg/kg SQ every 48 h for three treatments. Six turtles of each species were used for the study, and blood samples were taken at multiple time intervals. The terminal half-life after the last dose for the Kemp's ridley sea turtles was calculated at 7.18 h, and for the green sea turtles at 23.71 h. Throughout the multiple injections, MLX concentrations remained above 0.57 µg/mL, a concentration targeted in humans for the analgesic and anti-inflammatory effects. No negative side effects or changes to blood parameters evaluated were observed during the study in either species. The results of this study suggest MLX should be administered SQ to Kemp's ridley sea turtles at a dosage of 1 mg/kg every 12 h and in green sea turtles at a dose of 1 mg/kg every 48 h. The novelty of this work is that it is a multiple-injection study. Multiple injections were administered and produced concentrations that were considered therapeutic in humans, and the turtles did not have any adverse side effects. Furthermore, there were large differences in the pharmacokinetic values between green and Kemp's ridley sea turtles.

A Decerebrate Preparation of the Rattlesnake, Crotalus durissus, Provides an Experimental Model for Study of Autonomic Modulation of the Cardiovascular System in Reptiles

AbstractThe South American rattlesnake, Crotalus durissus, has been successfully used as an experimental model to study control of the cardiovascular system in squamate reptiles. Recent technical advances, including equipment miniaturization, have lessened the impact of instrumentation on in vivo recordings, and an increased range of anesthetic drugs has improved recording conditions for in situ preparations. Nevertheless, any animal-based experimental approach has to manage limitations regarding the avoidance of pain and stress the stability of the preparation and duration of experiments and the potentially overriding effects of anesthesia. To address such aspects, we tested a new experimental preparation, the decerebrate rattlesnake, in a study of the autonomic control of cardiovascular responses following the removal of general anesthesia. The preparation exhibited complex cardiovascular adjustments to deal with acute increases in venous return (caused by tail lifting), to compensate for blood flow reduction in the cephalic region (caused by head lifting), for body temperature control (triggered by an external heating source), and in response to stimulation of chemoreceptors (triggered by intravenous injection of NaCN). The decerebrate preparation retained extensive functional integrity of autonomic centers, and it was suitable for monitoring diverse cardiac and vascular variables. Furthermore, reanesthetizing the preparation markedly blunted cardiovascular performance. Isoflurane limited the maintenance of recovered cardiovascular variables in the prepared animal and reduced or abolished the observed cardiovascular reflexes. This preparation enables the recording of multiple concomitant cardiovascular variables for the study of mechanistic questions regarding the central integration of autonomic reflex responses in the absence of anesthesia.

Histamine exerts both direct H2-mediated and indirect catecholaminergic effects on heart rate in pythons

The vertebrate heart is regulated by excitatory adrenergic and inhibitory cholinergic innervations, as well as non-adrenergic non-cholinergic (NANC) factors that may be circulating in the blood or released from the autonomic nerves. As an example of NANC signaling, an increased histaminergic tone, acting through stimulation of H₂ receptors, contributes markedly to the rise in heart rate during digestion in pythons. In addition to the direct effects of histamine, it is also known that histamine can reinforce the cholinergic and adrenergic signaling. Thus, to further our understanding of the histaminergic regulation of the cardiovascular response in pythons, we designed a series of in vivo experiments complemented by in vitro experiments on sinoatrial and vascular ring preparations. We demonstrate the tachycardic mechanism of histamine works partly through a direct binding of cardiac H₂ receptors and in part through a myocardial histamine-induced catecholamine release, which strengthens the sympathetic adrenergic signaling pathway.

The vasopressor action of angiotensin II (ANG II) in ball pythons (Python regius)

Angiotensin II (ANG II) is part of the renin-angiotensin system (RAS) in vertebrates and exert vasoconstriction in all species studied. The present study examines the vasopressor effect of ANG II in the ball python (Python regius), and examines whether ANG II exert its effect through direct angiotensin receptors or through an activation of α-adrenergic receptors. The studies were conducted in snakes with chronic arterial catheters that had recovered from anesthesia. In addition to demonstrating a clear and pronounced dose-dependent rise in arterial blood pressure upon repeated injections of boluses with ANG II (0.001-1 μg/kg), we demonstrate that the pressor response persisted following α-adrenergic blockade using the α-adrenergic antagonist phentolamine (2.5 mg/kg). Unfortunately, it proved impossible to block the ANG receptors using losartan (1, 3 or even 10 mg/kg). The pressor response to ANG II was associated with a significant rise in heart rate at the higher dosages, pointing to a resetting of the barostatic mechanism for heart rate regulation. The responses were similar in fasting and digesting pythons despite the expected rise in baseline values for blood pressure and heart rate of the digesting snakes.

Endothelin-1 induces a strong pressor effect in ball pythons (Python regius)

Endothelin-1 (ET-1) is a very potent vasoactive peptide released from endothelial cells, and ET-1 plays an important role in the maintenance and regulation of blood pressure in mammals. ET-1 signaling is mediated by two receptors: ET_A and ET_B. In mammals, ET_A receptors are located on vascular smooth muscle where they mediate vasoconstriction. ET_B receptors located on the endothelium mediate vasodilatation through the release of nitric oxide, whereas stimulation of ET_B receptors placed on vascular smooth muscle leads to vasoconstriction. Less is known about ET-1 signaling in reptiles. In anaesthetized alligators, ET-1 elicits a biphasic blood pressure with a long-lasting initial decrease followed by a smaller increase in systemic blood pressure. In anaesthetized freshwater turtles, ET-1 causes a dose-dependent systemic vasodilatation mediated through ET_B receptors. In the present study, we investigated the cardiovascular effects of ET-1 on the systemic and pulmonary vasculature of pythons. The presence of ET_A and ET_B receptors in the vasculature of pythons was verified by means of immunoblotting. Myography on isolated vessels revealed a dose-dependent vasoconstrictory response to ET-1 in both mesenteric and pulmonary arteries. Pressure measurements in recovered specimens revealed an ET-1-induced rise in systemic blood pressure supporting our in vitro findings. In conclusion, our study shows that ET-1 induces a strong pressor effect in the systemic circulation.

Pharmacokinetics of subcutaneously administered hydromorphone in bearded dragons (Pogona vitticeps) and red-eared slider turtles (Trachemys scripta elegans)

OBJECTIVE

To determine pharmacokinetic dosing strategy in bearded dragons (Pogona vitticeps) and red-eared sliders (Trachemys scripta elegans) based on two subcutaneously (SC) administered doses of hydromorphone (0.5 and 1.0 mg kg^-1).

STUDY DESIGN

Randomized crossover study.

ANIMALS

Six healthy adult bearded dragons, seven healthy adult red-eared slider turtles.

METHODS

Hydromorphone (0.5 and 1.0 mg kg^-1; 2 mg mL^-1) was administered SC dorsolateral to the scapulae in the bearded dragons and between the head and thoracic limb of the red-eared slider turtles. Blood was collected for hydromorphone plasma concentration analysis from the ventral tail vein in bearded dragons and subcarapacial sinus in turtles before (time 0) hydromorphone administration and at 0.5, 1, 6, 12 and 24 hours.

RESULTS

The half-life of hydromorphone administered at 0.5 and 1.0 mg kg^-1 was 2.54 and 3.05 hours in bearded dragons and 2.67 and 2.01 hours in red-eared sliders, respectively. The maximum plasma concentrations for 0.5 and 1.0 mg kg^-1 were 142 and 369 ng mL^-1 in bearded dragons and 1610 and 5142 ng mL^-1 in red-eared sliders, respectively. Peak plasma concentrations were detected at 30 minutes for both species. Hydromorphone administered at both dosages provided plasma concentrations of 13-14 ng mL^-1 for at least 24 hours in bearded dragons and of 5-6 ng mL^-1 for at least 12 hours in red-eared sliders. Clinical sedation was observed for up to 1 hour posthydromorphone (1.0 mg kg^-1) administration for five of six bearded dragons characterized by low body carriage and decreased response to stimuli. No evidence of clinical sedation was observed in red-eared sliders at either dose.

CONCLUSIONS AND CLINICAL RELEVANCE

Recommended dosing strategy for hydromorphone is 0.5 mg kg^-1 administered SC every 24 hours in bearded dragons and every 12-24 hours in red-eared sliders.

The effects of morphine on gas exchange, ventilation pattern and ventilatory responses to hypercapnia and hypoxia in dwarf caiman (Paleosuchus palpebrosus)

Morphine and other opioids cause respiratory depression in high doses and lower the ventilatory responses to hypoxia and hypercapnia in mammals. Recent studies indicate that turtles respond similarly, but although they are used routinely for post-surgical analgesia, little is known about the physiological effects of opioids in reptiles. We therefore investigated the effects of morphine (10 and 20 mg kg^-1) on gas exchange and ventilation in six dwarf caiman (Paleosuchus palpebrosus) using pneumotachography in a crossover design. Intraperitoneal injections of morphine changed the ventilation pattern from a typical intermittent/periodic pattern with a few or several breaths in ventilatory bouts to single breaths and prolonged the apnoea, such that respiratory frequency was depressed, while tidal volume was elevated. Furthermore, the duration of inspiration and especially expiration was prolonged. The resulting decrease in minute ventilation was attended by a lowering of the respiratory exchange ratio (RER) (especially for 20 mg kg^-1 dose) indicating CO₂ retention with a long time constant for approaching the new steady state. The changes in ventilation pattern and gas exchange reached a new stable level approximately 3 h after the morphine injection and did not significantly affect steady state O₂ uptake, i.e. O₂ consumption. As expected, the ventilatory response to 5% O₂ was lower in morphine-treated caimans, but minute ventilation upon exposure to 2% CO₂ did not differ significantly different from control animals.

Pain and Its Control in Reptiles

Reptiles have the anatomic and physiologic structures needed to detect and perceive pain. Reptiles are capable of demonstrating painful behaviors. Most of the available literature indicates pure μ-opioid receptor agonists are best to provide analgesia in reptiles. Multimodal analgesia should be practiced with every reptile patient when pain is anticipated. Further research is needed using different pain models to evaluate analgesic efficacy across reptile orders.

Antinociceptive and respiratory effects following application of transdermal fentanyl patches and assessment of brain μ-opioid receptor mRNA expression in ball pythons

OBJECTIVE To quantify plasma fentanyl concentrations (PFCs) and evaluate antinociceptive and respiratory effects following application of transdermal fentanyl patches (TFPs) and assess cerebrospinal μ-opioid receptor mRNA expression in ball pythons (compared with findings in turtles). ANIMALS 44 ball pythons (Python regius) and 10 turtles (Trachemys scripta elegans). PROCEDURES To administer 3 or 12 μg of fentanyl/h, a quarter or whole TFP (TFP-3 and TFP-12, respectively) was used. At intervals after TFP-12 application in snakes, PFCs were measured by reverse-phase high-pressure liquid chromatography. Infrared heat stimuli were applied to the rostroventral surface of snakes to determine thermal withdrawal latencies after treatments with no TFP (control [n = 16]) and TFP-3 (8) or TFP-12 (9). Breathing frequency was measured in unrestrained controls and TFP-12-treated snakes. μ-Opioid receptor mRNA expression in brain and spinal cord tissue samples from snakes and turtles (which are responsive to μ-opioid receptor agonist drugs) were quantified with a reverse transcription PCR assay. RESULTS Mean PFCs were 79, 238, and 111 ng/mL at 6, 24, and 48 hours after TFP-12 application, respectively. At 3 to 48 hours after TFP-3 or TFP-12 application, thermal withdrawal latencies did not differ from pretreatment values or control treatment findings. For TFP-12-treated snakes, mean breathing frequency significantly decreased from the pretreatment value by 23% and 41% at the 24- and 48-hour time points, respectively. Brain and spinal cord tissue μ-opioid receptor mRNA expressions in snakes and turtles did not differ. CONCLUSIONS AND CLINICAL RELEVANCE In ball pythons, TFP-12 application resulted in high PFCs, but there was no change in thermal antinociception, indicating resistance to μ-opioid-dependent antinociception in this species.

EVALUATION OF FEEDING BEHAVIOR AS AN INDICATOR OF PAIN IN SNAKES

The necessity to prevent and manage pain in reptiles is becoming increasingly important, as their use in scientific research and popularity as exotic pets continues to rise. It was hypothesized that feeding behavior would provide an adequate indicator of pain perception in the ball python (Python regius). Normal feeding was defined the previous week, where a dead rodent was struck within 12 sec (n = 10). Eighteen pythons were randomly assigned to one of three treatments: anesthesia only (AO), chemical noxious stimulus (CS; capsaicin injection), or surgical noxious stimulus (SS; surgical incision). The time to strike was recorded 4 hr after the procedure and weekly during the subsequent 3 wk. Delayed feeding was observed in animals in the CS and SS groups, and normal feeding resumed after 1 and 3 wk, respectively. Spontaneous feeding remained uninterrupted for the AO group. These findings demonstrate feeding behavior as a potential model to assess pain in snakes.

Radio Transmitter Implantation and Movement in the Wild Timber Rattlesnake ( Crotalus horridus )

Radiotelemetry transmitters have become critical to studies of wildlife ecology. However, little is known about how transmitter implantation surgery affects the mobility of some species, including the timber rattlesnake, Crotalus horridus . Tracking snake movement can provide insights into the effects of transmitter implantation. During 2007-11, 71 radio transmitters were surgically implanted intracoelomically in 47 timber rattlesnakes. Over 20 of these snakes underwent surgery at least twice in 5 yr to replace old transmitters. Surgeries were performed under general anesthesia with a local nerve block at the site of implantation, 20 cm cranial to the cloaca. Snakes were also administered postsurgical meloxicam and enrofloxacin every 24 h for three doses. Two to five days after surgery, snakes were released at their original locations and radiotracked regularly during the active seasons (April-October 2007-11). Average daily movement data (distance traveled) were compiled for each snake. Snakes undergoing transmitter surgery in a given year did not differ significantly in distance traveled compared to snakes that had transmitters but did not have surgery in that year. Distance traveled for each snake did not differ before or after surgery or between weeks 1 and 2 postsurgery, indicating that the transmitter implantation did not alter snake movement.

Improved cardiac filling facilitates the postprandial elevation of stroke volume in Python regius

To accommodate the pronounced metabolic response to digestion, pythons increase heart rate and elevate stroke volume, where the latter has been ascribed to a massive and fast cardiac hypertrophy. However, numerous recent studies show that heart mass rarely increases, even upon ingestion of large meals, and we therefore explored the possibility that a rise in mean circulatory filling pressure (MCFP) serves to elevate venous pressure and cardiac filling during digestion. To this end, we measured blood flows and pressures in anaesthetized Python regius The anaesthetized snakes exhibited the archetypal tachycardia as well as a rise in both venous pressure and MCFP that fully account for the approximate doubling of stroke volume. There was no rise in blood volume and the elevated MCFP must therefore stem from increased vascular tone, possibly by means of increased sympathetic tone on the veins. Furthermore, although both venous pressure and MCFP increased during volume loading, there was no evidence that postprandial hearts were endowed with an additional capacity to elevate stroke volume. In vitro measurements of force development of paced ventricular strips also failed to reveal signs of increased contractility, but the postprandial hearts had higher activities of cytochrome oxidase and pyruvate kinase, which probably serves to sustain the rise in cardiac work during digestion.

Oxygen transport is not compromised at high temperature in pythons

To evaluate whether the 'oxygen and capacity limited thermal tolerance' model (OCLTT) applies to an air-breathing ectothermic vertebrate, we measured oxygen uptake (V̇(O₂)), cardiac performance and arterial blood gases during a progressive rise of temperature from 30 to 40°C in the snake Python regius. V̇(O₂) of fasting snakes increased exponentially with temperature whereas V̇(O₂) of digesting snakes at high temperatures plateaued at a level 3- to 4-fold above fasting. The high and sustained aerobic metabolism over the entire temperature range was supported by pronounced tachycardia at all temperatures, and both fasting and digesting snakes maintained a normal acid-base balance without any indication of anaerobic metabolism. All snakes also maintained high arterial PO2, even at temperatures close to the upper lethal temperature. Thus, there is no evidence of a reduced capacity for oxygen transport at high temperatures in either fasting or digesting snakes, suggesting that the upper thermal tolerance of this species is limited by other factors.

Surgical treatment of injuries caused by fishing gear in the intracoelomic digestive tract of sea turtles

We report the surgical techniques used to remove accidentally ingested hooks and branchlines localized in different parts of the digestive tract of 129 loggerhead sea turtles Caretta caretta, together with the characteristics and localization of lesions, and final outcome related to their severity. Hooks were removed from the cervical esophagus via the ventral surface of the neck, while the supraplastron approach was performed for hooks wedged in the intracoelomic portion of the esophagus. An approach through the left axillary region was preferred for fishhooks in the stomach, while hooks and long branchlines in the intestine or pyloric area were removed by approaching the coelomic cavity through the right or left prefemoral fossa. The ingestion of fishhooks, and/or longlines, often induces severe injuries in the digestive tract that could lead to the death of the turtles, with the extent of damage engendered by lines often more severe than that caused by hooks, leading to strangulation, intussusception, and tears that require resection of long tracts of intestine. Spontaneous expulsion of hooks, even where possible, involves long waiting times, with the possible impairment of the turtle's clinical condition, and should be avoided when the line is evident or suspected. The development of diversified surgical techniques enabled us to approach the coelomic cavity with minimally invasive and easy-to-perform methods, and survival rates proved very satisfactory.

Reduction of blood oxygen levels enhances postprandial cardiac hypertrophy in Burmese python (Python molurus)

Physiological cardiac hypertrophy is characterized by reversible enlargement of cardiomyocytes and changes in chamber architecture, which increase stroke volume and VO2 max via augmented convective oxygen transport. Cardiac hypertrophy is known to occur in response to repeated elevations of O2 demand and/or reduced O2 supply in several species of vertebrate ectotherms, including postprandial Burmese pythons (Python molurus). Recent data suggest postprandial cardiac hypertrophy in P. molurus is a facultative rather than obligatory response to digestion, though the triggers of this response are unknown. Here we hypothesize that an O2 supply-demand mismatch stimulates postprandial cardiac enlargement in Burmese pythons. To test this hypothesis, we rendered animals anemic prior to feeding, essentially halving blood oxygen content during the postprandial period. Fed anemic animals had heart rates 126% higher than fasted controls, which, coupled with a 71% increase in mean arterial pressure suggests fed anemic animals were experiencing significantly elevated cardiac work. We found significant cardiac hypertrophy in fed anemic animals, which exhibited ventricles 39% larger than fasted controls and 28% larger than fed controls. These findings support our hypothesis that those animals with a greater magnitude of O2 supply-demand mismatch exhibit the largest hearts. The "low O2 signal" stimulating postprandial cardiac hypertrophy is likely mediated by elevated ventricular wall stress associated with postprandial hemodynamics.

Comparative evaluation of the cadaveric, radiographic and computed tomographic anatomy of the heads of green iguana (Iguana iguana), common tegu (Tupinambis merianae) and bearded dragon (Pogona vitticeps)

Background

Radiology and computed tomography are the most commonly available diagnostic tools for the diagnosis of pathologies affecting the head and skull in veterinary practice. Nevertheless, accurate interpretation of radiographic and CT studies requires a thorough knowledge of the gross and the cross-sectional anatomy. Despite the increasing success of reptiles as pets, only a few reports over their normal imaging features are currently available. The aim of this study is to describe the normal cadaveric, radiographic and computed tomographic features of the heads of the green iguana, tegu and bearded dragon.

Results

6 adult green iguanas, 4 tegus, 3 bearded dragons, and, the adult cadavers of : 4 green iguana, 4 tegu, 4 bearded dragon were included in the study. 2 cadavers were dissected following a stratigraphic approach and 2 cadavers were cross-sectioned for each species. These latter specimens were stored in a freezer (−20°C) until completely frozen. Transversal sections at 5 mm intervals were obtained by means of an electric band-saw. Each section was cleaned and photographed on both sides. Radiographs of the head of each subject were obtained. Pre- and post- contrast computed tomographic studies of the head were performed on all the live animals. CT images were displayed in both bone and soft tissue windows. Individual anatomic structures were first recognised and labelled on the anatomic images and then matched on radiographs and CT images. Radiographic and CT images of the skull provided good detail of the bony structures in all species. In CT contrast medium injection enabled good detail of the soft tissues to be obtained in the iguana whereas only the eye was clearly distinguishable from the remaining soft tissues in both the tegu and the bearded dragon.

Conclusions

The results provide an atlas of the normal anatomical and in vivo radiographic and computed tomographic features of the heads of lizards, and this may be useful in interpreting any imaging modality involving these species.

Humoral regulation of heart rate during digestion in pythons (Python molurus and Python regius)

Pythons exhibit a doubling of heart rate when metabolism increases several times during digestion. Pythons, therefore, represent a promising model organism to study autonomic cardiovascular regulation during the postprandial state, and previous studies show that the postprandial tachycardia is governed by a release of vagal tone as well as a pronounced stimulation from nonadrenergic, noncholinergic (NANC) factors. Here we show that infusion of plasma from digesting donor pythons elicit a marked tachycardia in fasting snakes, demonstrating that the NANC factor resides in the blood. Injections of the gastrin and cholecystokinin receptor antagonist proglumide had no effect on double-blocked heart rate or blood pressure. Histamine has been recognized as a NANC factor in the early postprandial period in pythons, but the mechanism of its release has not been identified. Mast cells represent the largest repository of histamine in vertebrates, and it has been speculated that mast cells release histamine during digestion. Treatment with the mast cell stabilizer cromolyn significantly reduced postprandial heart rate in pythons compared with an untreated group but did not affect double-blocked heart rate. While this study indicates that histamine induces postprandial tachycardia in pythons, its release during digestion is not stimulated by gastrin or cholecystokinin nor is its release from mast cells a stimulant of postprandial tachycardia.

Change of cardiac function, but not form, in postprandial pythons

Pythons are renowned for a rapid and pronounced postprandial growth of the heart that coincides with a several-fold elevation of cardiac output that lasts for several days. Here we investigate whether ventricular morphology is affected by digestive state in two species of pythons (Python regius and Python molurus) and we determine the cardiac right-to-left shunt during the postprandial period in P. regius. Both species experienced several-fold increases in metabolism and mass of the digestive organs by 24 and 48 h after ingestion of meals equivalent to 25% of body mass. Surprisingly there were no changes in ventricular mass or dimensions as we used a meal size and husbandry conditions similar to studies finding rapid and significant growth. Based on these data and literature we therefore suggest that postprandial cardiac growth should be regarded as a facultative rather than obligatory component of the renowned postprandial response. The cardiac right-to-left shunt, calculated on the basis of oxygen concentrations in the left and right atria and the dorsal aorta, was negligible in fasting P. regius, but increased to 10-15% during digestion. Such shunt levels are very low compared to other reptiles and does not support a recent proposal that shunts may facilitate digestion in reptiles.

Pain and nociception in reptiles

The ability of reptiles to "feel" pain and the significance of pain or nociception on physiologic homeostasis is an exceedingly complex question requiring integration of both physiologic and behavioral evidence. Until further information is available, it would seem most ethical for veterinarians to assume that reptiles are capable of feeling pain, and to treat or manage pain when there is reasonable evidence that pain is present. With increased information available regarding analgesic use in reptiles and with the heightened awareness of the importance of analgesia for zoologic companion animals, it is likely that more veterinarians will provide pain relief to their reptile patients.

Tramadol use in zoologic medicine

Numerous analgesics are available for use in animals, but only a few have been used or studied in zoologic species. Tramadol is a relatively new analgesic that is available in an inexpensive, oral form, and is not controlled. Studies examining the effect of tramadol in zoologic species suggest that significant differences exist in pharmacokinetics parameters as well as analgesic dynamics. This article reviews the current literature on the use of tramadol in humans, domestic animals, and zoologic species.