Morphogenesis of the paleoamygdala during the early juvenile period in rats.

Structural rearrangements in the paleoamygdala during the early juvenile period of development were characterized in studies on 40 Wistar rats of both sexes on days 21, 24, 28, and 31 of postnatal life. Serial frontal sections of the brain stained with cresyl violet by the Nissl method were used to study the cytoarchitectonics of structures within the paleoamygdala (the dorsomedial (Med), the posterior medial (Mep), and posterior cortical (Cop) nuclei) and the dynamics of their formation by recording of planimetric characteristics, with measurements of the numbers of neurons and gliocytes and calculation of glial and apoptotic indexes. The results obtained from these experiments provided evidence for heterochronous morphogenesis and sex-related differences in the differentiation of paleoamygdalar structures. Only the Med was differentiated on day 21 (the beginning of the early juvenile period), while the Mep could be recognized on day 24 and the Cop acquired its characteristic cytoarchitectonics only on day 31 (the beginning of the late juvenile period). Significant gender-related differences in structure were seen in the Med from day 28 and in the Cop and Mep on day 31.