Purpose. VIP is a 28-aminoacid acid peptide belonging to the secretin family of peptides. It was originally isolated from porcine intestine by Said and Mutt(1970) and later shown to be distributed widely in the nervous system and in the gastrointestinal tract. It has been reported that VIP immunoreactivity has been detected immunocytochemically in certain amacrine cells of mammalian retinae studied to date. This study was performed to define the morphology and the synaptic connectivity of VIP immunoreactive neurons of the rat retina. Methods. Immunocytochemical staining using antibody against VIP was done on wholemounted and 50μm thick vibratome sections of the rat retina. Morphology and synaptic connectivity of VIP labeled cells were observed with light and electron microscopes. Results. VIP immunoreactive neurons were two types of bisratified amacrine cells located in the inner nuclear layer, which could be identified according to the size of their somata and the branching pattern of their processes. The type I cells were about 6-7 μm in diameter of the somata and their processes were stratified in sublaminae 1 and 5 of the inner plexiform layer. The type II cells had larger sized (about 10 μm in diameter) somata, and their processes were stratified in sublaminae 1, 3 and 5 of the IPL. The cell densities of type I and II cells in the central region were 371.9±81.5/mm2 and 22.4±6.4/mm2, respectively. The most common output targets of VIP immunoreactive amacrine cells onto amacrine cells, followed by onto ganglion cells throughout the IPL. The bipolar cells were not output targets of VIP labeled amacrine cells. VIP immunoreactive amacrine cells received most of their synaptic inputs from unlabeled amacrine cells in the IPL. Conclusion. These results provide that VIP might act as neuroactive substance and VIP released from VIP containing amacrine cells might affect ganglion cells directly via synapses onto ganlion cells or indirectly via synapses onto amacrine cells.
|Journal||Investigative Ophthalmology and Visual Science|
|State||Published - 15 Feb 1996|