Embryonic and larval development of NADPH-diaphorase/nitric oxide synthasereactivity in the brain of the amphibian Pleurodeles waltl

The distribution of NOS-containing cells was studied in the newt Pleurodele s walti during ontogenesis by means of nitric oxyde synthase (NOS) immunoch emistry and NADPH-diaphorase histochemistry. Embryonic and larval stages we re studied. The first positive neurons were observed at embryonic stage 30 in the ventrolateral area of the caudal rhombencephalon. Subsequently (stag e 33b), weakly reactive cells appeared rostrally in the mesencephalic tegme ntum, isthmic tegmentum. A general caudorostral gradient of newly expressin g NADPHd reactivity cells was observed through larval life. As in the adult , the nitrergic cells in the CNS of the newt are widely distributed during development, pointing to important roles of nitric oxyde through ontogenesi s. The sequence of appearance of nitrergic cells revealed a first involveme nt of this system in reticulospinal control likely influencing locomotor be havior. As development proceeds, cells in different sensory systems express progresively the enzyme NOS in a pattern that shows many similarities with other anamniotes.