“…In dentate gyrus, 85% of granule cells are generated between P0 (postnatal day 0) and P7 (Altman and Das, 1965;Bayer, 1980). The total number of CA1 pyramidal neurons remains essentially constant after birth (Boss et al, 1987;Cimadevilla et al, 1997;Sarkisian et al, 1999); however, from 3 to 25 months, the packing density in striatum pyramidale decreases by one-third (Knox, 1982). In striatum radiatum and moleculare, dendritic arborization and the formation of synaptic connections is apparent up to P45 (Pokorny and Yamamoto, 1981a,b), while the spine density on basal and apical dendrites increases significantly between P30 and P90 (Harris et al, 1992;Cintra et al, 1997).…”