The development of synapses in the cerebellar cortex of the chick embryo.

Abstract

Synaptogenesis was studied in the cerebellar cortex of chicken embryos from 7 1/2 days through 8, 8 1/2, 9, 10, 12, 14, and 18 days of incubation and one day post hatching (day 22). The earliest axo-dendritic synapses were found in the prospective molecular layer at 7 1/2 days; they were characterized by a slight, symmetrical membrane thickening and very few synaptic vesicles (2–3 per section). By day 9 the number of synapses had increased, there were more synaptic vesicles per terminal (ca. 10 per section) and the membrane thickenings were slightly asymmetrical. At day 10 morphologically mature synapses appeared, e.g. more synaptic vesicles and further membrane differentiation was observed. Synapses on dendritic spines of Purkinje cells appeared at day 18 and were abundant in the hatchling.