This study tested the prophylactic and the therapeutic efficacy of
memantine (1-amino-3,5-dimethyl-amandate), a clinically tested
N-methyl-D-aspartate (
NMDA) receptor antagonist, in suppressing
carrageenan-induced
thermal hyperalgesia in rats. Rats were injected with 0.1 ml of 1%
carrageenan solution s.c. into the right hindpaw, and exhibited
hyperalgesia in the injected paw as evidenced by a significant reduction of withdrawal latencies from baseline 1, 3, 5, and 24 h following
carrageenan. Prophylactic injection of
memantine, 10 and 15 mg/kg, significantly 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-
carrageenan. Therapeutic injection of 10 mg/kg of
memantine (2.5 h post-
carrageenan) had no effect. The 15 mg/kg dose produced a small effect (peak 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 tendency to produce a
therapeutic effect) on
carrageenan-induced
hyperalgesia at doses that do not significantly alter other motor behaviors.