Nitric oxide activation modulates olfactory fear generalization. All mice were trained with E5 odor and foot shock and tested with the trained odor, E5, as well as with one of the two structurally similar odors, E4 or E6. (A) Wild-type mice display significantly less freezing to E4 compared with E5. Knockout mice show reduced freezing to the trained odor compared with wild-type group, with no statistical differences to similar odors, suggesting increased generalization. (B) Pretraining injections of nitric oxide donor molsidomine increase freezing in knockout mice, with no significant differences in freezing levels between odors. (C) Pretraining injections of the nNOS blocker L-NAME in wild-type mice decrease the amount of freezing with no statistical differences between odors. (*) Significant difference from the E5 group, P < 0.05.
