STRUCTURAL CHANGES IN NAIVE RETINAL SYNAPSES DETECTABLE WITHIN MINUTES OF FIRST EXPOSURE TO DAYLIGHT

Retinal receptor terminals increase in width during prolonged exposure of rats to darkness, and subsequently decrease in width after exposure to daylight for only 3 min. Synaptic vesicles are dispersed in the large terminals in the dark, but concentrated in the smaller terminals of light-exposed rats, the total number remaining roughly constant. The postsynaptic processes were unusually dark in rats exposed to daylight for short times. Synaptic vesicles did not change in diameter in light or dark conditions, but were smaller near the synaptic ribbon than elsewhere in the same terminals. © 1969.