Neuronal changes in the amygdala basolateral complex were studied during development and maturation in fetal and postnatal rat brains using morphometrical methods. Forty brains of animals of various ages were fixed in formalin, frozen and cut into 25 microm thick sections and stained with cresyl violet or haematoxylin and eosin (H&E). In cresyl violet preparations, the complex appeared for the first time on embryonic day (E)17 and was composed of two homogeneous nuclei lateral and basolateral. On about the seventh postnatal day, each of these nuclei was divided into two parts the first one into the dorsolateral and ventromedial and the second one into the anterior and posterior. Morphometric investigations showed a different increase of the neuronal and nuclear size in various parts of the basolateral complex up to postnatal day (P)14; after that time these parameters did not change significantly. The neuronal density and the total number of neurons stabilized at P7 in all parts of this complex, except for the dorsolateral part of the lateral nucleus in which a 30% decrease of the total number of cells was observed. From P14, in all nuclei under study, the total number of neurons did not change significantly.
Development and maturation of the basolateral complex of the amygdaloid body were studied in fetal and postnatal rat brains. In cresyl violet-stained sections the basolateral complex was distinguishable at the 17th prenatal day. On about the 14th postnatal day, it showed all the features of the adult structure. The acetylcholinesterase activity appeared in neuropil of the basolateral complex on the seventh postnatal day; it increased slowly up to the 60th day. After that age, the acetylcholinesterase activity was stable in all parts of the basolateral complex and corresponded to its cytoarchitectonic differentiation. Our results suggest that the process of maturation of the amygdaloid basolateral complex, being related to the ingrowing of the cholinergic fibers from the basal forebrain, lasts at least up to the end of the second month of postnatal life.
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