Coexistence of pancreatic polypeptide and substance P in the chicken retina

The present immunohistochemical study using flat-mounted and frozen sections has revealed that in the chicken retina, pancreatic polypeptide (PP)-, such as avian pancreatic polypeptide (APP) and neuropeptide Y (NPY), and substance P (SP)-like immunoreactive (PPI and SPI) amacrine cells are composed of more heterogeneous subpopulations than has hitherto been supposed. Furthermore, using double-staining immunohistochemical procedures, we demonstrate that a substantial proportion of some subtypes of PPI cells contain SPI and that the ratio of both PPI and SPI cells to total immunoreactive cells differs according to the retinal portions and cell types.