Developmental pattern of NADPH-diaphorase activity in the peripheral nervous sistem of the cichlid fish Tilapia mariae

The distribution of NADPH-diaphorase: activity was studied in the cichlid f ish Tilapia mariae, during the first developmental stages by means of the t etrazolium salt technique. The reaction product was first found, 48 hours a fter fertilization (stage 10), in the cells of the olfactory placodes and i n the superficial neuromasts. A faint positivity was Seen in some hair cell s of the otic vesicles. The epithelial cells of the most caudal part of the intestinal tract showed a strong labeling. At stage 12 (hatch), the reacti on product was in addition detected:in scattered enteric neurons surroundin g the digestive tract. At stage 13 (4.5 days after spawning), the reaction product was also found in the putative sympathetic trunk, which supplies th e gill arches and digestive tract. The epithelial cells of the gastrointest inal canal showed a more strong positive labeling and two large clusters of cells near the pronephritic tubules (the putative adrenomedullar tissue) w ere also labeled. The present results indicate an early activity of NADPH-d iaphorase during the development of the peripheral nervous system of Tilapi a and reveal a gradual maturation of NADPH-diaphorase positive structures.