LEONARD,C.M.*; MAYS, L.; BRANDONI, C.; MONTES,C.; MENON, J.: The Role Of Nitric Oxide In Amphibian Development

The role of nitric oxide (NO), a free radical, as a novel intercellular signal molecule in embryonic development of several organisms has been well documented. In addition, NO has been also shown to be involved in remodeling of the spinal cord and thyroxine induced tail regression in anuran tadpoles. In this study, the distribution of NADPH- diaphorase (NADPH-d) activity was studied in Xenopus laevis tadpoles during embryonic and post-embryonic development by the histochemical reaction of NADPH-diaphorase that indicates the presence of nitric oxide synthase (NOS), the enzyme responsible for nitric oxide production. Developmental stages were designated according to Nieuwkoop and Faber, (1967). The highest activity appeared at stage 37/38 and by stage 46/47, NADPH-d activity was widely distributed in brain especially in olfactory lobes, cerebral hemispheres and cerebellum which could be due to development of neuronal connectivities and synaptic plasticity. By the time tadpoles reached stage 52, there was complete lack of NADPH-d activity in the brain. In this study we also show the enhancement of NADPH-d staining in response to retinol and retinol/thyroxine treatment in vitro. At the molecular level, the levels of mRNA for NOS increased significantly in response to these treatments. In conclusion, we propose a role for NO as a hormone-sensitive trigger, beginning the complicated cascade of events that lead to the remodeling of brain and regression of tissues such as tail during amphibian metamorphosis. The presence and distribution of this enzyme in evolutionarily distant animals from mammals adds information about the role of nitric oxide in development.