The antinociceptive effects of D-AP5 in rats with compression of the trigeminal nerve root. The effects of D-AP5, a non-selective NMDA site 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 the ipsilateral (A) or contralateral (B) side. However, 10 or 20 μg injections of AP5 increased the air-puff threshold significantly in a dose-dependent manner on both sides (A, B). These anti-allodynic effects of AP5 were maintained for three hours after injection. The intracisternal administration of 10 or 20 μg of AP5 also decreased the pin-prick scores ipsilateral (C) as well as contralateral (D) to the compression of the trigeminal nerve root. These anti-hyperalgesic effects of AP5 were completely recovered by six hours after injection. Vehicle injections did not affect pin-prick scores in the subject rats. *P < 0.05, vehicle-vs. AP-5-treated groups.