The postnatal development of synapses in the different laminae of the visual cortex in the normal kitten and in kittens with eyelid suture.

The postnatal development of synapses in the different laminae of the visual cortex has been studied in normal kittens and in kittens with unilateral or bilateral eyelid suture. In general, in normal kittens all laminae underwent basically the same two phases of development as for the cortex as a whole: an initial rapid rise to a peak at about 70 days of age, followed by a reduction in the density of asymmetric axospinous synapses towards the adult levels. There was no indication of a significant reduction in any other type of synapse. Lamina IV did not appear to have a peak density at 70 days of age, but there was a gradual decline after this age in the synaptic density toward adulthood, as for other laminae. The effects of eyelid suture were different for each lamina. On average, the density of synapses in the supragranular laminae underwent an initial retardation in the rate of development followed by a rise to a higher than normal peak at 70 days, and then a fall to below normal adult levels. The infragranular laminae also underwent an initial reduced rate of growth and never acquired their normal adult levels. Lamina IV was the least affected. Much of the changes in the development of synapses involved asymmetric axo-spinous synapses, with a small reduction in the number of symmetric synapses chiefly in lamina IV.