Figure 1.

Chronic morphine administration potentiated gp120-induced hyperalgesia. (a) Temporal diagram of drug administration. Gp120 and morphine were administrated by intrathecal and intraperitoneal injection, respectively, to simulate chronic presence. At day 21, the mice were euthanized for molecular and cellular analyses. (b) Threshold of mechanical pain (hyperalgesia) in the hind paw was measured by von Frey tests. Pain behavioral test was performed 5 h postmorphine injection. (c) Statistical comparison of the data points among groups in the shaded area in panel (b). Morphine exacerbation of gp120-induced pain started to express after day 6. With this administration paradigm, morphine alone did not cause significant hyperalgesia (p > 0.05). (**p < 0.01; ***p < 0.001; one-way analysis of variance, n = 6).