Figure 8.

Some second messengers not involved in type II priming. The groups of rats that had been treated with repeated (hourly, ×4) intradermal injections of DAMGO (1 μg) on the dorsum of the hindpaw 6 d before received, in a dose of 1 μg at the same site, injection of vehicle (control, black bars) or of the inhibitors of intracellular messengers wortmannin (PI3K), Z-VAD-FMK (caspase), U-73122 (PLCγ), l-NMMA (nitric oxide synthase), and quin-2 (calcium). Ten minutes later, PGE₂ (100 ng) was injected and mechanical hyperalgesia was evaluated 30 min and 4 h after PGE₂. In all groups, we observed that PGE₂ induced significant hyperalgesia that was still present when evaluated 4 h after injection, ruling out the involvement of these second messengers in type II priming. n = 6 paws per group.