THERMAL, MECHANICAL AND CHEMICAL PERIPHERAL SENSATION IN AMPHIBIANS -OPIOID AND ADRENERGIC EFFECTS

The acetic acid test (AAT) is a quantifiable assay of the response to noxious chemical stimuli on the hindlimb of tile northern grass frog, Rana pipens. AAT is sensitive to both opioid and adrenergic agonist mo dulation. The present study introduces the novel use of mechanical and thermal stimulus behavioral assays in comparison with tile establishe d acetic acid test in studying nociception in frogs. We evaluated mech anical and thermal responses and their sensitivity to systemic morphin e (MOR) or dexmedetomidine (DEX) administrations with comparison to AA T. MOR produced dose-related elevations of response thresholds in all three sensory tests, whereas DEX produced elevations in the thermal an d AAT assays but had no effect on sensitivity to non-noxious mechanica l stimuli. The results suggest a distinct separation of sensory modali ties in the frog similar to that observed in mammals and indicate the usefulness of this amphibian model in further studies of nociception.