(+)-HA 966, a partial agonist at the glycine site coupled to NMDA receptors, blocks formalin-induced pain in mice.

(+)-(1-Hydroxy-3-aminopyrrolidine-2-one) ((+)-HA 966), a partial agonist at the glycine site coupled to N-methyl-D-aspartic acid (NMDA) receptors, abolished the late phase of licking induced by injection of formalin into the hind-paw of mice; inhibitory dose50 (ID50) = 1.6 mg/kg, s.c. In contrast, it was weakly active against the first phase; ID50 = 33.3 mg/kg, s.c. Further, (+)-HA 966 was inactive in the rotarod test of ataxia. These data support a role of NMDA receptors in the transmission of prolonged noxious stimulation and suggest that partial glycine receptor agonists may exert antinociceptive properties against persistent pain.