Rapid determination of the thermal nociceptive threshold in diabetic rats

Painful diabetic neuropathy (PDN) is characterized by hyperalgesia i.e., increased sensitivity to noxious stimulus, and allodynia i.e., hypersensitivity to normally innocuous stimuli. Hyperalgesia and allodynia have been studied in many different rodent models of diabetes mellitus. However, as stated by Bölcskei et al, determination of "pain" in animal models is challenging due to its subjective nature. Moreover, the traditional methods used to determine behavioral responses to noxious thermal stimuli usually lack reproducibility and pharmacological sensitivity. For instance, by using the hot-plate method of Ankier, flinch, withdrawal and/or licking of either hind- and/or fore-paws is quantified as reflex latencies at constant high thermal stimuli (52-55 °C). However, animals that are hyperalgesic to thermal stimulus do not reproducibly show differences in reflex latencies using those supra-threshold temperatures. As the recently described method of Bölcskei et al., the procedures described here allows for the rapid, sensitive and reproducible determination of thermal nociceptive thresholds (TNTs) in mice and rats. The method uses slowly increasing thermal stimulus applied mostly to the skin of mouse/rat plantar surface. The method is particularly sensitive to study anti-nociception during hyperalgesic states such as PDN. The procedures described bellow are based on the ones published in detail by Almási et al and Bölcskei et al. The procedures described here have been approved the Laboratory Animal Care and Use Committee (LACUC), Wright State University.