Effect of nitric oxide synthesis inhibition on c-Fos expression in hippocampus and cerebral cortex following two forms of learning in rats: an immunohistochemistry study

This study investigated the effect of NO on c-Fos expression using immunocy tochemical techniques, following training in the one-trial passive avoidanc e response and Morris water maze tasks. Fos-like immunoreactive (FLI) neuro ns were examined in the hippocampus and cerebral cortex of rats in which in tracerebroventricular (i.c.v.) injection of N-omega-nitro-L-arginine (NAME) was given 30 min before training in the experimental groups. The results s howed that: (1) when compared with untreated rats or rats receiving i.c.v. saline injection, fos-like immunoreactive neurons were significantly increa sed in both brain regions following training in either task, and (2) preced ing i.c.v. injections of NAME blocked both the formation of memory and the increased expression of c-Fos in both brain regions subjected to training o n the two models. These results suggest that NO production may be a critica l factor for the formation of memory and the enhanced c-Fos expression, and so might contribute to the long-term plasticity of synaptic organization i n the two brain regions. (C) 1999 Lippincott Williams & Wilkins.