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Abstract
Synapse formation and several other developmental features of potential functional significance were followed by electron microscopy in mouse retina through the postnatal developmental period. Tight junctions between pigment epithelial cells, which are postulated to play a possible role in blood retina barriers, were well established in the newborn animal. Observations pertaining to receptor outer segment development indicated that saccule formation began between the fifth and sixth postnatal days and appeared to occur by a process of plasma membrane invagination. The formation of various types of synaptic complexes in both plexiform layers was studied in an attempt to ascertain the sequence in which these complexes mature in developing retina. Although layering phenomena observed with the light microscope suggest that retinal maturation proceeds from inner to outer levels of the retina, with ganglion cells maturing first and receptors last, this did not appear to be the sequence with which synapses matured. Synaptic developments began early and proceeded rapidly in receptor terminals in contrast to inner retinal components which showed a relative lag in achieving synaptic maturity. This finding is discussed in light of certain electroretinographic data on developing retina which suggest that at least some aspects of functional maturation proceed centripetally from outer to inner levels of the retina.