Hydrolyzes the sphingolipid ceramide into sphingosine and free fatty acid at an optimal pH of 6.5-7.5. Acts as a key regulator of sphingolipid signaling metabolites by generating sphingosine at the cell surface. Regulates synaptic vesicle exocytosis and trafficking by controlling presynaptic terminal sphingolipid composition. an N-acylsphing-4-enine + H2O = a fatty acid + sphing-4-enine Widely expressed in different tissues but enriched in neurons at all stages of development. N-glycosylated. Overexpression rescues retinal degeneration in arrestin and phospholipase C mutants, probably by facilitating membrane turnover and endocytosis of rhodopsin in photoreceptors. Belongs to the neutral ceramidase family.