Analgesic Efficacy of Tramadol and Morphine in White's Tree Frogs (Litoria caerulea).

Published data are sparse regarding the recognition of clinically relevant pain and appropriate analgesia in amphibians. The amphibian analgesia literature has primarily focused on nociceptive pathways in a single species, the northern leopard frog (Rana pipiens). The objective of the current study was to assess the analgesic efficacy and safety of oral tramadol and subcutaneous morphine in a commonly maintained zoo and pet species, White's tree frog (Litoria caerulea). We hypothesized that tramadol and morphine would provide dose-dependent antinociception, as measured by significant increases in hindlimb withdrawal latency after exposure to a noxious thermal stimulus. Two randomized, placebo-controlled, complete crossover studies were performed, with tramadol (n = 12) administered at 15, 25, and 40 mg/kg PO and morphine (n = 12) administered at 5 and 10 mg/kg SC. Hindlimb withdrawal latency was measured for a maximum of 72 h. No adverse side effects or signs of sedation were observed with any dose or drug evaluated. No significant difference in withdrawal latency was detected between the control and either tramadol or morphine. These negative results were surprising, suggesting that the thermal nociceptive model may not be biologically relevant in amphibian species.

Hypoxia switches episodic breathing to singlet breathing in red-eared slider turtles (Trachemys scripta) via a tropisetron-sensitive mechanism.

Hypoxia-induced changes in the chelonian breathing pattern are poorly understood. Thus, breathing was measured in freely swimming adult red-eared slider turtles breathing air prior to breathing nitrogen for 4h. Ventilation increased 10-fold within 10min due to increased breath frequency and tidal volume. Breaths/episode decreased by ∼50% within after 1h of hypoxia while the number of singlet breaths increased from 3.1±1.6singlets/h to a maximum of 66.1±23.5singlets/h. Expiratory and inspiratory duration increased during hypoxia. For doublet and triplet breaths, expiratory duration increased during the first breath only, while inspiratory duration increased for all breaths. Tropisetron (5-HT3 receptor antagonist, 5mg/kg) administration prior to hypoxia attenuated the hypoxia-induced increase in singlet breath frequency. Along with results from previous in vitro studies, this study suggests that 5-HT3 receptor activation may be required for the hypoxia-induced increase in singlet breathing pattern in red-eared slider turtles.