THE EFFECTS OF THE CLINICALLY TESTED NMDA RECEPTOR ANTAGONIST MEMANTINE ON CARRAGEENAN-INDUCED THERMAL HYPERALGESIA IN RATS

This study tested the prophylactic and the therapeutic efficacy of mem antine (1-amino-3,5-dimethyl-amandate), a clinically tested N-methyl-D -aspartate (NMDA) receptor antagonist, in suppressing carrageenan-indu ced thermal hyperalgesia in rats. Rats were injected with 0.1 ml of 1% carrageenan solution s.c. into the right hindpaw, and exhibited hyper algesia in the injected paw as evidenced by a significant reduction of withdrawal latencies from baseline 1, 3, 5, and 24 h following carrag eenan. Prophylactic injection of memantine, 10 and 15 mg/kg, significa ntly suppressed the hyperalgesia 1, 3, and 5 h post-carrageenan, with maximal effects of 70% (10 mg/kg) and 90% (15 mg/kg) at 1 h post-carra geenan. Therapeutic injection of 10 mg/kg of memantine (2.5 h post-car rageenan) had no effect. The 15 mg/kg dose produced a small effect (pe ak of 44%) at 3.5 h but not at a statistically significant level, and had no effect 5 h post-carrageenan. This study provides evidence that memantine produces primarily a prophylactic effect (and has only a ten dency to produce a therapeutic effect) on carrageenan-induced hyperalg esia at doses that do not significantly alter other motor behaviors.