The antinociceptive effects of PPPA in rats with compression of the trigeminal nerve root. The effects of PPPA, a competitive NR2A antagonist, on mechanical allodynia (A, B) and hyperalgesia (C, D) in rats with compression of the trigeminal nerve root (n = 8 in each treatment group). The intracisternal administration of vehicle did not affect air-puff thresholds in either ipsilateral or contralateral side. However, 1 or 10 μg injections of PPPA significantly increased the air-puff threshold in a dose-dependent manner both ipsilateral (A) and contralateral (B) to the compression of the trigeminal nerve root. The anti-allodynic effects of PPPA were maintained for one hour after a 1 μg injection of PPPA and six hours after a 10 μg dose of PPPA. The intracisternal administration of 1 or 10 μg of PPPA also significantly decreased the pin-prick scores on both sides (C, D). The anti-hyperalgesic effects of PPPA had completely recovered by six hours after the 10 μg PPPA injection. *P < 0.05, vehicle-vs. PPPA-treated groups.