Synapses of the inner plexiform layer of the area centralis of kitten retina during postnatal development: a quantitative study.

The frequency of occurrence of conventional synapses in the inner plexiform layer of the area centralis of the kitten retina remained invariant with postnatal age while that of bipolar cell ribbon synapses increased significantly. A significant increase also occurred in the ratio of bipolar cell ribbons to conventional synapses. The counts were made from large montages of electron micrographs in 17 kittens of ages ranging from newborn to 200 days and also in 3 adults. It was confirmed that the observed results were not attributable to an age-related change in the size or orientation of the profiles during postnatal development. The distribution of conventional synapses showed a peak in the middle stratum of the inner plexiform layer which remained invariant with development. By contrast, the distribution of bipolar cell ribbons changed during development, with new ribbons being added to the inner part of the inner plexiform layer.