NADPH-diaphorase histochemistry in the postnatal mouse cerebellum suggests specific developmental functions for nitric oxide.

NADPH-diaphorase histochemistry has been applied for the localization of nitric oxide synthase during the postnatal development of the mouse cerebellum. Staining for NADPH-diaphorase during the first week after birth was confined to some but not all laminae of the immature cerebellum: NADPH-diaphorase activity was located in the molecular/Purkinje cell layer and in inner parts of the internal granular layer. The external granular layer and the developing white matter were essentially unstained. Expression was earliest and very strong in parallel fibers and in the internal granule layer of the ventral part of the pyramis and the dorsal part of the uvula. Staining in the Purkinje cell layer was observed throughout the cerebellum. The presence of formazan deposits within Purkinje cells was verified by colocalization with calbindin D-28k immunoreactivity. The distribution of NADPH-diaphorase activity changed into the adult pattern between 8 and 12 days of age: Within the molecular layer, basket cells and their processes became strongly stained. Reaction product within Purkinje cells gradually disappeared. Likewise, strongly stained parallel fibers were no longer detectable. These results suggest that nitric oxide is involved in different processes in cerebellar development.