Paleoamygdala: The morphogenesis of nuclear-type, paleocortical and intermediate formations in the period of postnatal development in rats

Abstract

The cytoarchitectonics and expression of apoptosis (as an indicator of stabilization of formative processes) in nuclear, paleocortical, and intermediate formations of the paleoamygdala of the rat ondays 21, 24, 28, and 31 of postnatal development was studied. The results of analysis suggest that the morphogenesis of these formations is characterized by heterochrony due to the complexity of their structural organization predefined by the phylogenetic age. On day 21 of postnatal development of the rat, only the dorsomedial nucleus is well differentiated; on days 24-28, the posterior medial nucleus is well differentiated. The medial part of the posterior cortical nucleus (intermediate formation) is differentiated from the lateral part of this nucleus on day 28. The lateral part of the posterior cortical nucleus, which exhibits the characteristics of a paleocortical formation, acquires the cytoarchitectonics characteristic of an adult animal on day 31 of postnatal development. The dynamics of changes in the apoptotic index reflects the stabilization of morphogenetic processes characterized on the basis of cytoarchitectonic criteria. The results of this study and the neurogenetic data, indicating the presence of spatiotemporal gradients in the formation of the amygdaloid complex and the multiplicity of the original histogenetic domains, confirm the correctness of the previous concept (Akmaev and Kalimullina, 1993) on the substrate of this brain structure as a nuclear-paleocortical component of the brain.