Retinas were dissected, sectioned and mounted on slides, counterstained and analyzed for thickness of the inner plexiform, inner nuclear, outer nuclear and outer plexiform layers. Differences in the initiation and maturation rate of laminar thickness were compared between animal groups. Coronal sections were made through the hypothalamus and mounted on slides that were counterstained and analyzed for mean soma diameter of neurons within the SCN. Coronal sections through the SCN were examined for cytochrome oxidase (CYOX) staining both within the SCN and in the surrounding regions at each age. As a provocative test of SCN function, animals from each group were either exposed to a light pulse (LP) or not (NLP). Sections through the SCN and surrounding hypothalamus were immunohistochemically stained for c-Fos reactive neurons. Brain sections containing c-Fos labeled neurons were mounted, counterstained and examined by light microscopy to determine differences in the number of immunoreactive SCN neurons between LP and NLP animals at the age that the RHT projection becomes functional.

Results:

Histological examination of the retina revealed no differences in development between the Flight (FLT) and Flight Delayed Synchronous (FDS) retina at G20, PN1, PN3, and PN8. The pattern of cFos activation within the SCN of the G20 animals indicated that the FLT group was significantly delayed from the FDS group at this age. These differences disappeared by PN1. There was no difference between groups in the responsiveness of the SCN to light stimulation; a robust response was present by PN5.