Synaptic remodelling of perforated synapses during development and maturation in a visual projection area in birds

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Abstract
Perforated synapses are characterized by the appearance of one or more discontinuities in the postsynaptic density (PSD). These synapses are thought to represent intermediate stages in synaptic remodelling and turnover. To determine the dynamic level of these processes, the development of perforated synapses at different ages was examined in the neuropil of the ectostriatum, a visual projection area in birds. The overall number of perforated synapses per unit volume increases during development. Single and multeple perforated synapses, however, show a differnt developmental trend. Between 20 and 100 days, when the number of multiple perforated synapses decreases by 46%, single perforated synapses increase by 83% in number per unit volume. No significant changes in single or multiple perforated synapses can be observed at younger ages (i.e., 5 or 10 days). Various parameters increase between 10 and 20 days, followed by a reduction at 100 days: The relative frequency of perforations per synaptic contact, the length of the postsynaptic density including the size of the perforation, the length of the synaptic contact zone in perforated synapses excluding the size of the perforation, and the size of the perforation follow the same trend.