Prenatal and postnatal expression of nitric oxide in the developing kittensuperior colliculus revealed with NADPH diaphorase histochemistry

Nitric oxide (NO) is a neuronal messenger molecule that mediates pathway re finement in some brain regions. We used nicotinamide adenine dinucleotide p hosphate diaphorase (NADPHd) histochemistry to examine tile development of NO expression in the superior colliculus ISC) of kittens aged E28-E58 and P 2-P57 and adults in order to determine if NO expression is correlated with pathway refinement. At E28, labeled cells were seen only within the subvent ricular zone (SVZ). At E36-E41, labeled cells were also found within the de ep gray layer (DGL) of SC. Ar E51 and E58, a few labeled neurons were also present in the intermediate gray layer (IGL). These neurons already had ext ensive dendritic fields and well-developed morphologies at the time that th ey first expressed nitric oxide synthase (NOS). The number of neurons label ed in the DGL and IGL increased postnatally, reaching a peak density betwee n P14 and P35. Neurons within the optic (OL) and superficial gray layers (S GL) were first visible at P7 and increased slightly in number until adultho od. However, SGL-labeled neurons were relatively limited in number and ligh tly labeled at all ages examined. We conclude that (1) NADPHd expression oc curs in SC beginning in the second trimester in kittens and progresses in a ventral to dorsal pattern between E36-P35; (2) few neurons in kitten SGL a re labeled by NADPHd and these appear relatively late in postnatal developm ent; and (3) there is no correlation between NOS expression and retinocolli cular pathway refinement in kittens, a result different from that seen in r odents.