Laminar pattern of NADPH-diaphorase activity in the developing avian cerebellum.

The present study aimed to define the distribution of NADPH-diaphorase (NADPH-d) positive cells and fibers in the developing chick cerebellum. From embryonic day 9 (E9) until day E15 NADPH-d positive ascending axons, originating from pontine nuclei, targeted selectively the developing folia. Cerebellar cortex exhibited weak NADPH-d activity until day E15, when NADPH-d negative granule cells of external granular layer began inward migration. From that embryonic age, differentiated granule, Golgi II type cells and glomeruli of the internal granular layer exhibited gradually increasing diaphorase activity. In the molecular layer diffuse activity increased, possibly due to the development of the parallel fibers. Transient NADPH-d activity appeared on Purkinje somata (PC) at day E17 and by posthatching day 1 all PC were devoid of diaphorase activity. Our data support the hypothesis that neurons producing nitric oxide (NO) are involved in the activity dependent developmental processes for the establishment of connections and normal cytoarchitecture.