Developmental changes in heme-oxygenase-2 and bNOS expression in enteric neurons in the pig duodenum

There exists much parallelism between carbon monoxide- and nitric oxide-generating systems. Therefore, we wondered whether developmental and functional differences along the duodenum similarly affect, part of them, namely, heme oxygenase-2- (HO-2) and neural isoform of nitric oxide synthase- (nNOS) expressing neurons. By applying NADPH diaphorase histochemistry and HO-2 immunohistochemistry on whole-mount preparations and by using stereologic methods, a qualitative and quantitative description of HO-2 and nNOS expression was obtained. Examinations were carried out on the duodenum of fetal, neonatal and weaned pigs. At all ages, three enteric plexuses were readily distinguished. The presence of both enzymes fits in with other morphological and physiological reports. However, the expression of both enzymes significantly changed during development. The number of HO-2-IR neurons increased approximately 20-fold in the inner submucous and almost doubled in the myenteric plexus. In addition, the number of nNOS-expressing neurons displayed a significant decrease in the outer submucous plexus after weaning. High levels of glucocorticoids may cause the perinatally increased HO-2 expression, whereas an influence on nNOS expression is doubtful. Therefore, it seems that notwithstanding the high similarity between both systems, their expression is regulated differently in the pig duodenum.