PHARMACOKINETICS OF TRAMADOL AND O-DESMETHYLTRAMADOL IN GIANT TORTOISES (CHELONOIDIS VANDENBURGHI, CHELONOIDIS VICINA).

The objective of this study was to determine the pharmacokinetics of two orally administered doses of tramadol (1 mg/kg and 5 mg/kg) and its metabolite, O-desmethyltramadol (M1) in giant tortoises (Chelonoidis vandenburghi, Chelonoidis vicina). Eleven giant tortoises (C. vandenburghi, C. vicina) received two randomly assigned, oral doses of tramadol (either 1 mg/kg or 5 mg/kg), with a washout period of 3 wk between each dose. The half-life (t½) of orally administered tramadol at 1 mg/kg and 5 mg/kg was 11.9 ± 4.6 h and 13.2 ± 6.1 h, respectively. After oral administration of tramadol at 1 mg/kg and 5 mg/kg, the maximum concentration (Cmax) was 125 ± 69 ng/ml and 518 ± 411 ng/ml, respectively. There were not enough data points to determine pharmacokinetic (PK) parameters for the M1 metabolite from either dose. Tramadol administered orally to giant tortoises at both doses provided measurable plasma concentrations of tramadol for approximately 48 h with occasional transient sedation. Oral tramadol at 5 mg/kg, on average, achieves concentrations of >100 ng/ml, the reported human therapeutic threshold, for 24 h. Based on the low levels of M1 seen in this study, M1 may not be a major metabolite in this taxon.

COMPARISON OF SUBCUTANEOUS ADMINISTRATION OF ALFAXALONE-MIDAZOLAM-DEXMEDETOMIDINE WITH KETAMINE-MIDAZOLAM-DEXMEDETOMIDINE FOR CHEMICAL RESTRAINT IN JUVENILE BLUE POISON DART FROGS (DENDROBATES TINCTORIUS AZUREUS).

Blue poison dart frogs (Dendrobates tinctorius azureus) are commonly maintained in zoological institutions and are becoming popular in the pet trade industry. Sedation or light anesthesia is required for safe and effective handling of this species. In this study, the sedative effects of subcutaneously administered alfaxalone-midazolam-dexmedetomidine (AMD) (20, 40, 5 mg/kg, respectively) and ketamine-midazolam-dexmedetomidine (KMD) (100, 40, 5 mg/kg, respectively) were compared in a prospective, randomized, blinded, crossover study in juvenile blue poison dart frogs (n = 10). Both protocols were partially reversed 45 min after administration of either protocol with subcutaneously administered flumazenil (0.05 mg/kg) and atipamezole (50 mg/kg). Heart rate, pulmonic respiratory rate, various reflexes, and behavioral parameters were monitored after drug administration. Both protocols resulted in rapid loss of righting reflex [median (range): AMD, 5 min (5-5 min); KMD, 5 min (5-10 min)]. Time to complete recovery was similar with both protocols (mean ± SD: AMD, 97.5 ± 11.4 min; KMD, 96.5 ± 25.4 min). The AMD protocol resulted in pulmonic respiratory depression, whereas no significant difference in heart rate was found between the two protocols. All frogs were observed eating within 24 hr of chemical restraint. Gastric prolapses occurred in four frogs (AMD 3, KMD 1) that were easily reduced with a cotton-tip application. No other adverse reactions were observed. The results of this study provide two different subcutaneous chemical restraint protocols in juvenile blue poison dart frogs.

Comparison of subcutaneous dexmedetomidine-midazolam versus alfaxalone-midazolam sedation in leopard geckos (Eublepharis macularius).

OBJECTIVE: To compare dexmedetomidine-midazolam with alfaxalone-midazolam for sedation in leopard geckos (Eublepharis macularius). STUDY DESIGN: Prospective, randomized, blinded, complete crossover study. ANIMALS: Nine healthy adult leopard geckos. METHODS: Geckos were administered a combination of dexmedetomidine (0.1 mg kg-1) and midazolam (1.0 mg kg-1; treatment D-M) or alfaxalone (15 mg kg-1) and midazolam (1.0 mg kg-1; treatment A-M) subcutaneously craniodorsal to a thoracic limb. Heart rate (HR), respiratory rate (fR), righting reflex, palpebral reflex, superficial and deep pain reflexes, jaw tone and escape response were assessed every 5 minutes until reversal. Conditions for intubation and response to needle prick were evaluated. Antagonist drugs [flumazenil (0.05 mg kg-1) ± atipamezole (1.0 mg kg-1)] were administered subcutaneously, craniodorsal to the contralateral thoracic limb, 45 minutes after initial injection, and animals were monitored until recovery. RESULTS: HR, but not fR, decreased significantly over time in both treatments. HR was significantly lower than baseline at all time points in D-M and for all but the 5 and 10 minute time points in A-M. HR was significantly higher in A-M at all time points after drug administration when compared with D-M. Sedation scores between protocols were similar for most time points. All animals in A-M lost righting reflex compared with seven out of nine (78%) geckos in D-M. Geckos in A-M lost righting reflex for significantly longer time. Mean ± standard deviation time to recovery after antagonist administration was 6.1 ± 2.2 minutes for D-M and 56 ± 29 minutes for A-M, and these times were significantly different. CONCLUSIONS AND CLINICAL RELEVANCE: Combination D-M or A-M provided sedation of a level expected to allow physical examinations and venipuncture in leopard geckos. A-M provided a faster onset of sedation compared with D-M. Recovery was significantly faster following antagonist reversal of D-M, compared with A-M.

Bilateral Uveitis and Hyphema in a Catalina Macaw (Ara ararauna × Ara macao ) With Multicentric Lymphoma.

A 20-year-old, female Catalina macaw (Ara ararauna × Ara macao ) was presented with bilateral uveitis and hyphema. The hyphema initially improved with 0.12% prednisolone acetate ophthalmic drops (1 drop OU q4h for 7 days), but the hyphema recurred after the drops were tapered. The bird subsequently developed inappetance, weight loss, regurgitation, and lethargy and was euthanatized 24 days after initial presentation. Necropsy revealed marked splenomegaly and hepatomegaly, with significant mucosal ulcerations of the proventriculus and petechiation associated with both kidneys. Histopathologic examination revealed multicentric lymphoma, with neoplastic cells observed in ocular, splenic, hepatic, renal, proventricular, intestinal, pancreatic, and choanal tissue. Neoplastic lymphocytes effaced the iris, ciliary body, and the choroid of the eyes, and neoplastic lymphocytes were attached to the corneal endothelium and infiltrated the sclera, episclera, and conjunctivae. Immunohistochemical results indicated that the neoplastic lymphocytes were CD3(+) and CD79a(-), which is consistent with T-cell lymphoma.

ANESTHETIC INDUCTION AND RECOVERY PARAMETERS IN BEARDED DRAGONS (POGONA VITTICEPS): COMPARISON OF ISOFLURANE DELIVERED IN 100% OXYGEN VERSUS 21% OXYGEN.

Inland bearded dragons (Pogona vitticeps, n=6) were anesthetized for 1 hr using isoflurane in either 100% oxygen or 21% oxygen (FI 21; medical-grade room air). Parameters of anesthetic depth were recorded throughout both induction and recovery by an observer blinded to the fraction of inspired oxygen (FiO2), including the loss and return of withdrawal and righting reflexes, muscle tone, ability to intubate or extubate, and return to spontaneous respiration. Physiologic data were recorded every 5 min throughout the anesthetic procedures, including heart rate, body temperature, end-tidal CO2, hemoglobin oxygen saturation (SpO2), and percent expired isoflurane. Lizards were subjected to application of a noxious stimulus (needle stick) at 0, 30, and 60 min, and responses recorded. Following a minimum 7-day washout period, the experiment was repeated with each lizard subjected to the other protocol in a randomized, complete crossover design. The only statistically significant difference was a lower mean SpO2 in the group inspiring 21% oxygen (P<0.0020). No statistically significant differences were detected in any parameters during induction or recovery; however, all values were uniformly shorter for the FI 21 group, indicating a possible clinically significant difference. A larger sample size may have detected statistically significant differences. Further studies are needed to evaluate these effects in other reptile species and with the concurrent use of injectable anesthetic and analgesic drugs.

USE OF CORTICAL BONE FENESTRATION, AUTOGENOUS FREE SKIN GRAFT, AND THERMOGRAPHY FOR WOUND TREATMENT AND MONITORING IN A RED WOLF (CANIS RUFUS GREGORYI).

A 2-yr-old female red wolf (Canis rufus gregoryi) sustained a degloving injury to the left thoracic limb while in a display habitat. Initial attempts to resolve the extensive wound by using conservative measures were unsuccessful. Subsequent treatment using a free skin graft consisted first of establishment of an adequate granulation bed via cortical bone fenestration. After establishment of a healthy granulation bed was achieved, free skin graft was harvested and transposed over the bed. To monitor viability and incorporation of the graft, serial thermographic imaging was performed. Thermography noninvasively detects radiant heat patterns and can be used to assess vascularization of tissue, potentially allowing early detection of graft failure. In this case, thermography documented successful graft attachment.

PHARMACOKINETICS OF TRAMADOL AND O-DESMETHYLTRAMADOL IN LOGGERHEAD SEA TURTLES (CARETTA CARETTA).

The objective of this study was to determine the pharmacokinetics of two orally administered doses of tramadol (5 and 10 mg/kg) and its major metabolite (O-desmethyltramadol) (M1) in loggerhead sea turtles (Caretta caretta). After oral administration, the half-life of tramadol administered at 5 and 10 mg/kg was 20.35 and 22.67 hr, whereas the half-life of M1 was 10.23 and 11.26 hr, respectively. The maximum concentration (Cmax) for tramadol after oral administration at 5 mg/kg and 10 mg/kg was 373 and 719 ng/ml, whereas that of M1 was 655 and 1,376 ng/ml, respectively. Tramadol administered orally to loggerhead sea turtles at both dosages provided measurable plasma concentrations of tramadol and O-desmethyltramadol for several days with no adverse effects. Plasma concentrations of tramadol and O-desmethyltramadol remained ≥100 ng/ml for at least 48 and 72 hr when tramadol was administered at 10 mg/kg.

Evaluation of rebound tonometry in red-eared slider turtles (Trachemys scripta elegans).

OBJECTIVE: To evaluate feasibility and accuracy of intraocular pressure (IOP) measurement by rebound tonometry in adult red-eared slider turtles and determine the effects of manual and chemical restraint on IOP. ANIMAL STUDIED: Seventeen adult red-eared slider turtles. PROCEDURES: Intraocular pressure was measured with TonoLab® and TonoVet® tonometers in conscious, unrestrained turtles. To evaluate the effects of manual restraint, turtles were restrained by digital pressure on the rostral head or proximal neck. The effect of two chemical restraint protocols (dexmedetomidine, ketamine, midazolam [DKM] and dexmedetomidine, ketamine [DK] subcutaneously) on IOP was evaluated. Triplicate TonoLab® and TonoVet® readings were compared with direct manometry in three ex vivo turtle eyes. RESULTS: TonoLab® correlated better with manometry at IOPs < 45 mmHg than TonoVet® (linear regression slopes of 0.89 and 0.30, respectively). Mean (±SD) IOP in unrestrained conscious turtles was significantly lower (P < 0.01) with TonoLab® (10.02 ± 0.66 mmHg) than with TonoVet® (11.32 ± 1.57 mmHg). Manual neck restraint caused a significant increase in IOP (+6.31 ± 5.59 mmHg), while manual rostral head restraint did not. Both chemical restraint protocols significantly reduced IOP (DKM: −1.0 ± 0.76 mmHg; DK: −1.79 ± 1.17) compared with measurements in conscious unrestrained turtles. CONCLUSIONS: Chemical and manual neck restraint affected IOP. Rostral head restraint had no significant effect on IOP and is, therefore, recommended as the appropriate restraint technique in red-eared slider turtles. TonoLab® measurements estimated actual IOP more accurately, within physiologic range, than measurements obtained using the TonoVet®.

Lidocaine constant rate infusion improves the probability of survival in rabbits with gastrointestinal obstructions: 64 cases (2012-2021).

OBJECTIVE: To determine the survival to discharge rate of rabbits with gastrointestinal obstructions treated with lidocaine constant rate infusion (CRI) and other factors associated with survival. ANIMALS: Cases of gastrointestinal obstruction in rabbits (n = 56, including 64 events) that had presented to a veterinary teaching hospital from 2012 to 2021. METHODS: This was a retrospective study in which data on rabbits with evidence of gastrointestinal obstruction were extracted from veterinary teaching hospital medical records over a 9-year period. Systemic lidocaine treatment, breed, sex, age, temperature at presentation, blood glucose at presentation, and time to discharge or death were evaluated with univariate and multivariate logistic regression to identify factors significantly associated with survival to hospital discharge in rabbits with gastrointestinal obstruction. RESULTS: Comparatively, 89.7% of rabbits treated with lidocaine CRI (n = 39) survived to hospital discharge, while only 56% of rabbits that were not treated with lidocaine CRI (25) survived. In the final multivariate analysis, 2 factors were associated with survival to discharge: rabbits treated with systemic lidocaine and male rabbits had increased odds of survival compared to those not treated with systemic lidocaine and female rabbits, respectively. CLINICAL RELEVANCE: Results demonstrated that rabbits with gastrointestinal obstruction and treated with a lidocaine CRI were more likely to survive compared to rabbits not treated with lidocaine CRI.

Physiologic and serum biochemistry values in free-ranging Hoffmann's two-toed (Choloepus hoffmanni) and brown-throated three-toed (Bradypus variegatus) sloths immobilized using dexmedetomidine and ketamine.

Dexmedetomidine, a highly selective alpha-2 adrenergic agonist and dextrorotary enantiomer of medetomidine, was combined with ketamine and used to immobilize 14 free-ranging Choloepus hoffmanni (Hoffmann's two-toed sloths) and 11 Bradypus variegatus (brown-throated three-toed sloths) in Upala, Costa Rica. Following intramuscular injection of ketamine (2.1 mg/kg) and dexmedetomidine (11 microg/kg), heart rate, respiratory rate, and indirect systolic blood pressure were measured every 5 min for a total of 25 min. An iStat (CG8+) was used to evaluate serum biochemical and hematologic values during anesthesia. After 30 min of anesthesia, atipamezole (0.13 mg/kg) was administered intramuscularly, which resulted in rapid and smooth recoveries. Mean heart rate and respiratory rate remained unchanged in both C. hoffmanni and B. variegatus over time. Progressive decreases in mean indirect systolic blood pressure were documented in both species. Results of this study suggest a combination of dexmedetomidne and ketamine is a safe and effective anesthetic protocol for use in free-ranging C. hoffmanni and B. variegatus. Similar to other alpha-2 adrenergic agonist-based immobilization protocols, close monitoring of cardiovascular and respiratory parameters are recommended. This study also provides serum biochemical and hematologic data in free-ranging C. hoffmanni and B. variegatus.

Treatment of Pain in Fish.

This chapter provides an overview of our current understanding of clinical analgesic use in fish. Recently, the efficacy and pharmacokinetics of several analgesic drugs for use in fish have been investigated, and the most important data indicates that µ-opioid agonist drugs (e.g, morphine) are consistently effective as analgesics across fish species. In addition, bath application of some analgesic drugs may be useful, which affords multiple methods for delivering analgesics to fish. Although few published studies of non-steroidal anti-inflammatory drugs administered to fish show promise, we have much to learn about the analgesic efficacy of most drugs in this class.

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.

Antinociceptive efficacy of buprenorphine and hydromorphone in red-eared slider turtles (Trachemys scripta elegans).

Despite the frequent clinical use of buprenorphine in reptiles, its antinociceptive efficacy is not known. In a randomized, complete cross-over study, the antinociceptive efficacy of buprenorphine (0.2 mg/kg s.c.) was compared with hydromorphone (0.5 mg/kg s.c.), and saline (0.9% s.c. equivalent volume) in 11 healthy red-eared slider turtles (Trachemys scripta elegans). Additionally, buprenorphine at 0.1 and 1 mg/kg was compared with saline in six turtles. Hindlimb withdrawal latencies were measured after exposure to a focal, thermal noxious stimulus before and between 3 hr and up to 96 hr after drug administration. Buprenorphine did not significantly increase hindlimb withdrawal latencies at any time point compared with saline. In contrast, hydromorphone administration at 0.5 mg/kg significantly increased hindlimb withdrawal latencies for up to 24 hr. These results show that hydromorphone, but not buprenorphine, provides thermal antinociception in red-eared slider turtles.

Sedation and physiologic response to manual restraint after intranasal administration of midazolam in Hispaniolan Amazon parrots (Amazona ventralis).

Administration of intranasal midazolam (2 mg/kg) was evaluated for sedation and effects on cloacal temperature, respiratory rate, and heart rate in manually restrained Hispaniolan Amazon parrots (Amazona ventralis). Adult parrots (n=9) were administered either midazolam (2 mg/kg) or an equal volume of saline solution intranasally before a 15-minute manual restraint in a complete crossover study. Respiratory rate and sedation scores were recorded before and during capture and during and after 15 minutes of manual restraint. Heart rate and cloacal temperature were recorded during manual restraint. After restraint, the parrots received intranasal flumazenil (0.05 mg/kg) or an equal volume of saline solution, and the recovery time was recorded. In those birds that received midazolam, sedation was observed within 3 minutes of administration, and vocalization, flight, and defense responses were significantly reduced during capture. During manual restraint, the mean rate of cloacal temperature increase was significantly slower and remained significantly lower in birds that received midazolam compared with controls. Mean respiratory rates were significantly lower for up to 12 minutes in parrots that received midazolam compared with those receiving saline solution. Flumazenil antagonized the effects of midazolam within 10 minutes. No overt clinical adverse effects to intranasal midazolam and flumazenil administration were observed. Further studies on the safety of intranasal midazolam and flumazenil in this species are warranted.

Use of thermography and fluorescein angiography in the management of a Chilean flamingo with avascular necrosis of the wing.

A Chilean flamingo (Phoenicopterus chilensis) was presented to the veterinary clinic at the North Carolina Zoological Park for evaluation of acute weakness of the right wing. Results of a physical examination revealed a lack of a palpable pulse in the radial artery, which suggested occlusion or obstruction of the vessel. Radiography, thermography, and fluorescein angiography confirmed right wing injury and vascular compromise. Based on the poor prognosis for return to function associated with irreversible vascular damage, the wing was amputated. After a period of observation and treatment, the bird was returned to public exhibit.

Evaluation of the analgesic effects of oral and subcutaneous tramadol administration in red-eared slider turtles.

OBJECTIVE: To determine the dose- and time-dependent changes in analgesia and respiration caused by tramadol administration in red-eared slider turtles (Trachemys scripta). DESIGN: Crossover study. ANIMALS: 30 adult male and female red-eared slider turtles. PROCEDURES: 11 turtles received tramadol at various doses (1, 5, 10, or 25 mg/kg [0.45, 2.27, 4.54, or 11.36 mg/lb], PO; 10 or 25 mg/kg, SC) or a control treatment administered similarly. Degree of analgesia was assessed through measurement of hind limb thermal withdrawal latencies (TWDLs) at 0, 3, 6, 12, 24, 48, 72, and 96 hours after tramadol administration. Nineteen other freely swimming turtles received tramadol PO (5, 10, or 25 mg/kg), and ventilation (V(E)), breath frequency, tidal volume (V(T)), and expiratory breath duration were measured. RESULTS: The highest tramadol doses (10 and 25 mg/kg, PO) yielded greater mean TWDLs 6 to 96 hours after administration than the control treatment did, whereas tramadol administered at 5 mg/kg, PO, yielded greater mean TWDLs at 12 and 24 hours. The lowest tramadol dose (1 mg/kg, PO) failed to result in analgesia. Tramadol administered SC resulted in lower TWDLs, slower onset, and shorter duration of action, compared with PO administration. Tramadol at 10 and 25 mg/kg, PO, reduced the V(E) at 12 hours by 51% and 67%, respectively, and at 24 through 72 hours by 55% to 62% and 61 % to 70%, respectively. However, tramadol at 5 mg/kg, PO, had no effect on the V(E). CONCLUSIONS AND CLINICAL RELEVANCE: Tramadol administered PO at 5 to 10 mg/kg provided thermal analgesia with less respiratory depression than that reported for morphine in red-eared slider turtles.

Disseminated histoplasmosis in a Bengal tiger (Panthera tigris).

Disseminated infection with Histoplasma capsulatum was diagnosed in a 7-yr-old female Bengal tiger (Panthera tigris). Clinical signs were nonspecific with the exception of brief periods of tachypnea for 5 days prior to death. H. capsulatum organisms were found in the lungs, tracheobronchial lymph nodes, and liver. Diagnosis was confirmed by tracheal wash, urine H. capsulatum enzyme immunoassay, and necropsy results. This report represents the first published account of disseminated histoplasmosis in a tiger.

Hematology and clinical chemistry values of free-ranging basilisk lizards (Basiliscus plumifrons) in Costa Rica.

Twenty-three lizards were captured for this study, both males and females (12 males, 10 females, 1 undetermined), with a large range in body weights (40-286 g) appeared to be healthy based on activity level, physical examinations, and body condition scores. Heparinized blood samples from 20 free-ranging basilisk lizards (Basiliscus plumifrons) in Costa Rica were used for determining complete blood cell counts, plasma, and heparinized whole blood biochemical analysis. This information will serve as baseline reference data for future health assessment studies of free-ranging and captive basilisk lizards, as well as epidemiologic, conservation, and captive-breeding studies. A point-of-care analyzer was useful for this field study, and clinical chemistry values from heparinized whole blood samples were similar to values from plasma, which indicates that separation of plasma may not be necessary to process blood samples on site in remote areas. To the authors' knowledge, this is the first report of hematologic and plasma biochemical data from free-ranging B. plumnifrons.

Pharmacokinetics of ceftazidime in Northern leopard frogs (Lithobates pipiens) at two different doses and administration routes.

OBJECTIVE: To determine an optimal ceftazidime dosing strategy in Northern leopard frogs (Lithobates pipiens) by evaluation of 2 different doses administered SC and 1 dose administered transcutaneously. ANIMALS: 44 Northern leopard frogs (including 10 that were replaced). PROCEDURES: Ceftazidime was administered to frogs SC in a forelimb at 20 mg/kg (n = 10; SC20 group) and 40 mg/kg (10; SC40 group) or transcutaneously on the cranial dorsum at 20 mg/kg (10; TC20 group). Two frogs in each ceftazidime group were euthanized 12, 24, 48, 72, and 96 hours after drug administration. Plasma, renal, and skin concentrations of ceftazidime were measured by means of reversed-phase high-performance liquid chromatography. Four control frogs were used for assay validation. RESULTS: Mean plasma half-life of ceftazidime in the SC20, SC40, and TC20 groups was 9.01 hours, 14.49 hours, and too low to determine, respectively. Mean maximum plasma ceftazidime concentration was 92.9, 96.0, and 1.3 µg/mL, respectively. For 24 hours after drug administration in the SC20 and SC40 groups, plasma ceftazidime concentration exceeded 8 µg/mL. Renal and skin concentrations were detectable at both doses and routes of administration; however, skin concentrations were significantly lower than renal and plasma concentrations. CONCLUSIONS AND CLINICAL RELEVANCE: Findings indicated that ceftazidime administration to Northern leopard frogs at 20 mg/kg, SC, every 24 hours would achieve a plasma concentration exceeding the value considered effective against common amphibian pathogens. Transcutaneous administration of the injectable ceftazidime formulation at 20 mg/kg warrants further investigation but is not currently recommended because of a potential lack of efficacy.

Comparison of Thermal and Mechanical Noxious Stimuli for Testing Analgesics in White's Tree Frogs (Litoria caerulea) and Northern Leopard Frogs (Lithobates pipiens).

Determining the clinical efficacy of analgesic drugs in amphibians can be particularly challenging. The current study investigated whether a thermal nociceptive stimulus is useful for the evaluation of analgesic drugs in 2 amphibian species. The objectives of this study were 2-fold: 1) compare 2 models of nociception (thermal and mechanical) using 2 frog species; White's Tree Frogs (Litoria caerulea; WTF) and Northern Leopard Frogs (Lithobates pipiens; NLF) after administration of saline or morphine sulfate; and 2) evaluate antinociceptive efficacy of morphine sulfate at 2 doses in a common amphibian research species, the NLF, using a mechanical stimulus. Neither WTF nor NLF displayed consistent drug-dependent changes in withdrawal responses to a noxious thermal stimulus applied using the Hargreaves apparatus, but NLF exposed to the noxious mechanical stimulus demonstrated a significant dose-dependent antinociceptive response to morphine sulfate. These results indicate that morphine is not antinociceptive in WTF, supporting previously reported results, and demonstrate the importance of using an appropriate experimental antinociceptive test in amphibians. Our data suggest that nociception in amphibian species may be best evaluated by using mechanical nociceptive models, although species differences must also be considered.