Developmental pattern of NADPH-diaphorase activity in the peripheral nervous system of the cichlid fish Tilapia...

The distribution of NADPH-diaphorase activity was studied in the cichlid fish Tilapia mariae, during the first developmental stages by means of the tetrazolium salt technique. The reaction product was first found, 48 hours after fertilization (stage 10), in the cells of the olfactory placodes and in the superficial neuromasts. A faint positivity was seen in some hair cells 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 reaction product was in addition detected in scattered enteric neurons surrounding the digestive tract. At stage 13 (4.5 days after spawning), the reaction product was also found in the putative sympathetic trunk, which supplies the gill arches and digestive tract. The epithelial cells of the gastrointestinal canal showed a more strong positive labeling and two large clusters of cells near the pronephritic tubules (the putative adrenomedullar tissue) were also labeled. The present results indicate an early activity of NADPH-diaphorase during the development of the peripheral nervous system of Tilapia and reveal a gradual maturation of NADPH-diaphorase positive structures.