Antinociceptive effects of RB101(S), a complete inhibitor of enkephalin-catabolizing enzymes, are enhanced by (+)-HA966, a functional NMDA receptor antagonist: a c-Fos study in the rat spinal cord. - Buritova J; Le Guen S; Fournié-Zaluski MC; Roques BP; Besson JM (European journal of pain (London, England), 2003)