Asynchronous changes in size, number, and shape of synapses in the developing superior colliculus.

The ultra-structural development of synapses in retino-receptive layers of the opossum superior colliculus was studied by the ethanolic phosphotungstic acid (E-PTA) method. There was a tendency for a slight reduction in the diameter of synaptic disks, a rise and fall of numerical densities and, except for an ephemeral period, a general increase in the proportion of "frown" among curve synapses. The lack of strict synchrony and the occurrence of different patterns of changes suggest that multiple factors contribute to synaptic maturation.