Different effects of visual deprivation on vasoactive intestinal polypeptide (VIP)-containing cells in the retinas of juvenile and adult rats.

Vasoactive intestinal polypeptide (VIP) is a 28 amino acid peptide that has been shown to be present in a distinct subset of retinal amacrine cells (VIP+ cells). Previous work has suggested that the expression of retinal VIP might depend on the lighting conditions prevailing. Reasoning that a careful analysis of the exact conditions of this interaction and its time course might offer clues to the functional role of retinal VIP, we performed a quantitative immunohistochemical analysis of the effects of visual deprivation on the retinal VIP+ system in adult and in visually inexperienced neonatal rats. In adult rats visual deprivation caused a marked suppression of VIP-like immunoreactivity (IR) in both somata and processes of VIP+ cells which increased linearly over time, reducing the number of VIP+ cells to about 30% of the control value after approximately 50 days of deprivation. The observed changes were specific for VIP and were independent of the form of deprivation used (monocular lid suture versus keeping rats in constant darkness). However, the effects of visual deprivation were dependent on the developmental state of the rats, since juvenile rats without previous visual experience exhibited a decrease in VIP+ cells and fibers which was much smaller and occurred significantly slower than in adult rats. The suppression of VIP-like IR was completely reversible in both juvenile and adult rats when previously deprived rats were returned to a normal visual environment.