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 tha t has been shown to be present in a distinct subset of retinal amacrin e cells (VIP+ cells). Previous work has suggested that the expression of retinal VIP might depend on the lighting conditions prevailing. Rea soning that a careful analysis of the exact conditions of this interac tion and its time course might offer clues to the functional role of r etinal VIP, we performed a quantitative immunohistochemical analysis o f the effects of visual deprivation on the retinal VIP+ system in adul t and in visually inexperienced neonatal rats. In adult rats visual de privation 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 contr ol value after approximately 50 days of deprivation. The observed chan ges were specific for VIP and were independent of the form of deprivat ion used (monocular lid suture versus keeping rats in constant darknes s). However, the effects of visual deprivation were dependent on the d evelopmental state of the rats, since juvenile rats without previous v isual experience exhibited a decrease in VIP+ cells and fibers which w as much smaller and occurred significantly slower than in adult rats. The suppression of VIP-like IR was completely reversible in both juven ile and adult rats when previously deprived rats were returned to a no rmal visual environment.