7-Nitroindazole upregulates phosphorylated cAMP response element binding protein, polysialylated-neural cell adhesion molecule and tryptophan hydroxylase expression in the adult rat hippocampus

We examined the effect of nitric oxide (NO) on the expression of phosphorylated cAMP response element binding (pCREB) protein and on the polysialylated form of the neural cell adhesion molecule (PSA-NCAM), in the hippocampus of the adult rat, by administering 7-nitroindazole (7-NI) for 5 days, to block neuronal nitric oxide synthase (nNOS) activity. It was found that PSA-NCAM and pCREB immunoreactive cells were increased two-fold in the dentate gyrus by this treatment. In addition, the immunoreactivities of serotonin (5-HT, 5-hydroxytryptamine), known to be involved in neural plasticity, and of tryptophan hydroxylase immunoreactive-fibers in the dentate gyrus were both upregulated by 7-NI. Our results indicate that nNOS inhibition upregulates neural plasticity and increases 5-HT in the rat hippocampus, and suggest the existence of regulatory relationships between NO, neural plasticity and 5-HT.