A modified Hargreaves’ method for assessing threshold temperatures for heat nociception

• Published in: Journal of neuroscience methods 2013-09, Vol.219 (1), p.41-51
• Main Authors: Banik, Ratan K., Kabadi, Rajiv A.
• Format: Article
• Language: English
• Subjects: Aging - physiology; Analgesics - pharmacology; Animals; Data Interpretation, Statistical; Feedback, Physiological - physiology; Foot - innervation; Foot - physiology; Gabapentin; Hot Temperature; Hyperalgesia - physiopathology; Male; Morphine; Nociception; Nociception - drug effects; Nociception - physiology; Pain Measurement - methods; Pain Threshold - drug effects; Pain Threshold - physiology; Physical Stimulation; Radiant heat; Rat; Rats; Rats, Inbred F344; Rats, Sprague-Dawley; Sensory Thresholds - drug effects; Sensory Thresholds - physiology; Skin - innervation; Thermosensing - drug effects; Thermosensing - physiology; Threshold temperature
• ISSN: 0165-0270; 1872-678X
• DOI: 10.1016/j.jneumeth.2013.06.005

•We describe a method to measure threshold temperatures for heat nociception in rats.•The method relies on characterising average plantar epicutaneous temperatures.•We show similar degrees of incision-induced allodynia, and these effects are reversed using analgesics.•The method facilitates a comparison between the data obtained from animal models and human psychophysical studies. This study describes a modified Hargreaves’ method for assessing paw withdrawal threshold temperatures for heat (PWT-H) nociception in the hind paws of rats. This method utilises radiant heat to maintain controlled lamp temperatures (CLTs) on a glass floor beneath the rat hind paw. An ascending series of CLTs were applied for 10s, with 5–10min intervals between applications, until characteristic withdrawal behaviour was observed or a cutoff CLT was reached. The average plantar epicutaneous temperatures measured from anaesthetised rats corresponding to CLTs and withdrawal latencies were used for determining PWT-H. The mean PWT-H in 2-month-old (mo) naïve Sprague-Dawley rats (n=38) was 47.6±0.2°C, which is comparable to the noxious threshold temperature for human glabrous skin (46.5±0.5°C). The PWT-H was consistent between trials and daily assessments over four consecutive days. No significant differences were observed between the PWT-H in 2-, 6- to 8-, and >24-mo F344 rats, but the PWT-H in 1-mo rats was significantly reduced. Three hours following plantar incision, the PWT-H decreased to 37.5±0.2°C, consistent with previous observations of C-fibre afferents from incised glabrous skin firing at 36.7±3.6°C. Parallel testing, using the current method and an electronic von Frey device, illustrated similar degrees of incision-induced hyperalgesia, gradual improvements in hyperalgesia, and reversals induced through morphine and gabapentin. In conclusion, the present method facilitates a comparison of PWT-H using electrophysiological and human psychophysical studies involving thermosensation, and as a behavioural assay identical to von Frey testing, this method also measures the threshold for nociception.