Fig. 2.

Vaccination selectively prevents antinociception in designed opiate target, whereas therapeutic opioids maintain activity. Vaccinated rats were tested for thermal and mechanical sensitivity using the hot plate (A) and von Frey filament (B) tests, respectively. Her–KLH completely blocked heroin-induced antinociception, whereas codeine, buprenorphine, and methadone maintained effectiveness. Mor–KLH vaccination prevented morphine- and codeine-induced antinociception but not heroin-induced antinociception. n = 6–7 per group. The data are expressed as mean ± SEM; *P < 0.05, **P < 0.01, ***P < 0.001, compared with KLH controls (Dunnett’s post hoc test).