A NITRIC-OXIDE SYNTHASE INHIBITOR IMPAIRS MEMORY STORAGE IN MICE

Posttraining administration of the L-enantiomer of the competitive inh ibitor of nitric oxide synthase, N-G-nitro-L-arginine methyl ester (L- NAME, 3-100 mg/kg, ip), impaired 48-h retention of a one-trial step-th rough inhibitory shock-avoidance task in male Swiss mice. The effects were dose-dependent and were not observed when the D-enantiomer (D-NAM E, 3-100 mg/kg, ip) was injected instead of L-NAME. Retention latencie s of mice that had not received a footshock during training were not a ffected by L-NAME. The memory impairment produced by L-NAME was time-d ependent, suggesting an action on memory storage. The effects of L-NAM E on memory were overcome by the injection of L-(but not D-)arginine ( 300 mg/kg, ip) along with the inhibitor. Considered together, these fi ndings suggest that the L-arginine/nitric oxide pathway may be involve d in memory storage of an inhibitory avoidance response in mice. (C) 1 996 Academic Press, Inc.