Teuchert-Noodt G, Dawirs RR. Naturally occurring synapse degradation in the developing cerebellum of the mallard (Anas Platyrhynchos) and the Peking duck (Forma Domestica). J Hirnforsch. 1996;37(4):547-560.In order to analyze remodelling of junctions as component of adaptive mechanism in the developing avian cerebellum, a silver-staining technique was applied which is highly sensitive towards the detection of lysosomal aggregations (LA) in degrading synapses. LA was quantified in ducks at incubation ages from day 21 to 28 and from hatching up to 32 days. In the mallard, LA increased gradually throughout the whole investigation period, while in the Peking duck LA showed a dramatic increase in the perihatching period followed by the beginning of a decline at about 3 weeks of age. In both species LA occurred initially in the superficial molecular layer prehatching followed by a succession of degradative events down to the granular layer. LA dynamics thus coincide with the outside-in proliferation and differentiation of granule cells during advanced cortical histogenesis. Light microscopy of Epon sections impregnated with silver indicated that granule and Purkinje cell contacts were the center of LA dynamics. Electron microscopy confirmed that synapse degradation occurred predominantly with presynaptic elements of climbing, parallel and mossy afferents. As illustrated by the structural dynamics, maturation of cerebellar circuitry passes through a period of unbalanced synaptogenesis posthatching. Remarkably, the ongoing "critical period" of synaptogenesis in the mallard provides the opportunity for more differentiated behavioral pattern formation in the wild as compared to the domestic duckling
