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. Author manuscript; available in PMC: 2016 Mar 1.
Published in final edited form as: Addict Biol. 2013 Dec 13;20(2):275–284. doi: 10.1111/adb.12120

Figure 1.

Figure 1

(A) Mechanical sensitivity responsiveness following single vs. repeated heroin exposure. Rats were administered heroin (1.25 mg/kg, SC, n = 8) for five days and tested for paw withdrawal thresholds 1, 3, and 6 h post-heroin injection on day 1 and day 5. The magnitude of the increase in threshold at 1 h is lessened on day 5, while the thresholds at 0 h and 6 h are below day 1, indicating hyperalgesia. These neuroadaptations are hypothesized by Simonnet and colleagues to reflect a sensitization of pronociceptive systems (Celerier et al., 2001). Asterisks indicate a significant group effect (*** p < 001) between acute vs. chronic heroin-treated groups. (B) Paw withdrawal thresholds of heroin-treated rats continue to decrease over five days. On days 4 and 5, thresholds are significantly lower compared to baseline (* p < 0.05).