Polymorphous granular cells in the lung of the primitive fish, the bichir <i><scp>P</scp>olypterus senegalus</i>

Abstract

Abstract This study describes the distribution and the coexpression of specific neurochemical markers in both neuroendocrine‐like cells ( NEC ‐like) and polymorphous granular cells ( PGC s) that populate the mucociliated epithelium of the lung in the air‐breathing fish Polypterus senegalus , using confocal immunohistochemistry. Using confocal immunohistochemistry, we determined the coexpression of specific neurochemical markers. Colocalization studies showed that 5 HT is coexpressed with calbindin and nNOS and choline acetyltransferase (Ch AT ) is coexpressed with nNOS in the PGC s. This study also shows for the first time the simultaneous occurrence of piscidin 1 and 5 HT in the PGC s. The function of these cells being equivalent to ones found in fish gill subepithelial parenchyma is still not known. Due to the importance of piscidin 1 in local immune defence, more research is to be useful to understand a possible interaction of PGC s with immune response in the bichir lung. In fact, the capacity of PGC s to produce NO and other neuroactive substances found in immune cells of fish may represent a primitive form of immunoregulation of innate immunity and specifically antimicrobial function as NO induction and respiratory burst activity are correlated with immune response.