title: Characterization of variables defining hindpaw withdrawal latency evoked by radiant thermal stimuli.
abstract: We have examined the stability and sources of variation within the nociceptive model of rat hind paw withdrawal from an under-glass radiant stimulus (Hargreaves et al., 1988) using a system where stimulus intensity and floor temperature can be controlled and reproducibly changed. The current study demonstrates that: (i) increased stimulus intensity with a fixed surface temperature is associated with a monotonic decrease in mean response latency and its variance; (ii) for a fixed stimulus intensity, the mean paw withdrawal latency and variance increased as the glass floor temperature is lowered from 30 degrees C to room temperature (25 degrees C). Using subcutaneously-implanted thermocouples and a 30 degrees C glass surface, the subcutaneous paw temperature observed at an interval corresponding to the time at which the animal displayed a paw withdrawal did not differ across multiple heating rates (41-42.5 degrees C). This finding is in agreement with human studies of pain thresholds and C-fiber activity. These studies emphasize the importance of maintaining a fixed surface temperature to reduce experimental variability and the utility of this apparatus across multiple stimulus intensities to define agonist efficacy.
authors.affiliation: Department of Pharmacology, University of California, San Diego, La Jolla 92093-0818, USA.
authors.forename: D M
authors.initials: DM
authors.lastname: Dirig
authors.forename: A
authors.initials: A
authors.lastname: Salami
authors.forename: M L
authors.initials: ML
authors.lastname: Rathbun
authors.forename: G T
authors.initials: GT
authors.lastname: Ozaki
authors.forename: T L
authors.initials: TL
authors.lastname: Yaksh
mesh_terms: D000704:Analysis of Variance; D000818:Animals; D004924:Escape Reaction / Q000502:physiology*; D005898:Glass; D006614:Hindlimb; D006358:Hot Temperature; D006801:Humans; D008297:Male; D010147:Pain Measurement; D017288:Pain Threshold; D051381:Rats; D017207:Rats, Sprague-Dawley; D011930:Reaction Time / Q000502:physiology*; D015203:Reproducibility of Results; D012881:Skin Temperature; D013499:Surface Properties