The phenotypic data for opioid responses including analgesia, tolerance, dependence and OIH was collected for 23 inbred strains of mice. Subsets of this data were used in previous mapping efforts [8, 13, 14]. The behavior response of principal interest in these studies was OIH; a mechanical stimulus was used to characterize changes in nociceptive thresholds at baseline and after chronic morphine treatment (Figure 1). The percent reduction of mechanical nociceptive thresholds after chronic opioid treatment varied approximately 7-fold across the 23 strains analyzed. Of note, there was not a significant correlation between baseline mechanical threshold and the degree of OIH observed after chronic morphine treatment (P > 0.05). Additional file 1: Figure S1 provides data for other chronic opioid adaptive traits analyzed here, including: hindpaw OIH measured using Hargreave’s thermal testing, OIH measured using tail-flick thermal testing, analgesic tolerance and physical dependence.
