Developmental changes of synaptic proteins expression within the hippocampal formation of the rat

A properly structured neuronal network, which is a prerequisite of a correctly functioning central nervous system, depends on the proper construction of synaptic terminals. There are some studies concerning development of hippocampal cells, however, the data about maturation of the synaptic terminals network within the hippocampal formation are only fragmentary. The study was performed on Wistar rats of various ages. The following synaptic proteins: synaptophysin, SNAP-25 and GAP-43 (a growth axon cone protein) were used to study the maturation of synaptic terminals. We have found that, at the time of birth, the hippocampal formation is very immature. Synaptogenesis begins on P4 and lasts till P10 or P14. The strongest immunoreactivity of all proteins is observed at the beginning of this period. Thereafter, immunoreactivity decreases and, after P14, it is similar to that of adult animals. On P60 and P90, the level of immunoreactivity increases again. In the pyramidal and granular cell layers, the formation of synaptic terminals and their maturation occur earlier in embryonal life, and are almost completely mature at birth.