A freeze-fracture study of the maturation of synapses in the anteroventral cochlear nucleus of the developing rat.
The freeze-fracture technique was used to study the maturation of the postsynaptic membrane of spherical cells of the anteroventral cochlear nucleus (AVCN) of the developing rat brain. Observations were made at 2-day intervals from birth to 16 days of age. At all ages, the external leaflet (E-face) of the spherical cell membrane has aggregates of particles opposite presynaptic active zones. From birth to 6 days of age, these particle aggregates were found only on dendritic processes, not on the cell body. At 8 days of age, the aggregates were found on small somatic appendages and on the cell body adjacent to somatic appendages. In animals from 10 to 12 days of age, particle aggregates became increasingly common on the cell body. Morphometric analysis demonstrated a decrease in size but not packing density of the particles in the aggregates. These changes in the location and size of the aggregates correspond to the location of asymmetrical synapses seen in thin section material at these same time intervals (Neises et al., 1982). At 14 days the fracture plane no longer followed the postsynaptic membrane at the active zone; instead it shifted to the presynaptic membrane and the postsynaptic specializations were rarely seen. This fracture pattern is typical of adult animals.
D000375:Aging; D000818:Animals; D000831:Animals, Newborn; D003056:Cochlear Nerve / Q000254:growth & development / Q000648:ultrastructure*; D005614:Freeze Fracturing; D008854:Microscopy, Electron; D051381:Rats; D013569:Synapses / Q000648:ultrastructure*; D013570:Synaptic Membranes / Q000648:ultrastructure