Ontogeny of substance P-containing structures in the chicken retina: immunohistochemical analysis

We examined the ontogeny of the system with substance P-like immunoreactivity (SPI) in the chicken retina by indirect immunofluorescence method. Amacrine cells containing SPI first appeared at embryonic day 7 (E7) in the peripheral portion of the retina. At E8, they had increased in number and now extended medially to the central portion. They continued to increase in number, reaching a maximum between E13-15. After the chicks hatched, the number of SPI cells was unchanged. SPI fibers first appeared at E8 in the periphery. SPI fibers were both at the ora serrata and in the inner plexiform layer (IPL), which were not abundant. After E8, they increased in number. The increase was particularly rapid in the IPL between E10 and E16 and at the ora serrata between E15 and E19. SPI fibers reached the maximum number immediately after hatching. After that, SPI fibers in the IPL were unchanged in number. Those at the ora serrata decreased slightly in number with age, though SPI fibers were still numerous in the chicken retina 2 weeks and 1 month after hatching. These results showed that development of SPI is different for subtypes of SPI cells and for different location. This heterogeneity in development may reflect the functional differences of substance P depending on cell type and fiber location.