Comparative characterization of the basic forebrain cortical zones in Emys orbicularis (Linnaeus) and Testudo horsfieldi (Gray)

Abstract

The neuronal and synaptic organization of forebrain basic cortical zones in Testudo horsfieldi and Emys orbicularis and their dendritic spines have been studied using Nissle, Golgi and electron microscopic methods. It has been shown by comparison of the results that the two spicies have marked differences in the structural organization of the forebrain cortical zones. The cortical formation in Testudo horsfieldi is different from that of Emys orbicularis in a greater diversity of neuronal types, smaller size of neurons, smaller cell density in each cortical zones, the presence of horizontal dendritic terminals in dorsomedial dorsal cortex, the absence of the large neurons in dorsomedial medial cortex, ect. Moreover, in both species the dorsomedial dorsal cortex in comparison with medial and lateral cortex is characterized by a marked complexity of the structural organization (diverse neuronal composition, the presence of the stellate cells, the highest cell density, the smallest neuronal size). The investigation of spines in the different dendritic levels (proximal, middle and distal) of neurons in three cortical basic zones has been shown that in both species it has been observed the tendency to increasing of the spine density from proximal to distal part of dendrite. at all dendritic levels noninvaginated forms of spines predominated. Invaginated spines were recorded at the proximal and middle levels of dendrites and contain more organelles and inclusions than noninvaginated spines. In Testudo horsfieldi and Emys orbicularis differences of spine thin structure and spine density in the cortical basic zones were revealed. Moreover, in both species the spines of dorsomedial dorsal cortex were more numerous, more variable in shape, more abundant in organelles. It was there that a bush-like distribution of spines was found which in evidently a special form of synaptic organization of cortical neurons. The above features of this cortical zone indicates a higher degree of differentiation, suggesting that the dorsomedial dorsal cortex is phylogenetic youth as compared with hippocampus and lobus pyriformis.