Here, we describe a rapid reliable and simple procedure to determine the lowest temperature at which rats or mice show nocifensive behavior, i.e. the thermal nociceptive threshold (TNT). This method applies a slowly increasing thermal stimulus allowing precise and reproducible estimation of TNTs with minimum, if any, stress to the animals.
Painful diabetic neuropathy (PDN) is characterized by hyperalgesia i.e., increased sensitivity to noxious stimulus, and allodynia i.e., hypersensitivity to normally innocuous stimuli1. Hyperalgesia and allodynia have been studied in many different rodent models of diabetes mellitus2. However, as stated by Bölcskei et al, determination of “pain” in animal models is challenging due to its subjective nature3. Moreover, the traditional methods used to determine behavioral responses to noxious thermal stimuli usually lack reproducibility and pharmacological sensitivity3. For instance, by using the hot-plate method of Ankier4, 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 temperatures3,5. As the recently described method of Bölcskei et al.6, 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 5 and Bölcskei et al 3. The procedures described here have been approved the Laboratory Animal Care and Use Committee (LACUC), Wright State University.
Similarly to the classic hot plate test to quantify thermal hyperalgesia4,13, the assay of nociception described here permits a fast and reliable way to quantify nocifensive behavior in rats and mice. However, contrary to classic test, the incremental hot-plate method is non-invasive and virtually stress-free. Although some restrain is necessary to perform the test (i.e., the animal must be in the observation chamber), rats or mice are accustomed to similar areas (e.g., housing cages).
<…The authors have nothing to disclose.
This work was funded by the American Diabetes Association (ADA), Grant JF1-10-14 (MDiF). We would like to thank the personnel of the Laboratory of Animal Resources at WSU. Authors gratefully acknowledge assistance with the statistical analysis of data from Neil Paton, Ph.D.
Name | Company | Catalogue number |
Incremental Hot-Plate Analgesia Meter | IITC Inc. Life Science | Part #PE34 |
Soft Series 8 | IITC Inc. Life Science | Part # Series8 |
Streptozotocin | Calbiochem | 572201 |