Phylogenetic and ecological properties of the structural organization of the cortical plate in the forebrain of Chelonia. 2. Axo-spinal synaptic complexes of the plexiform layer of the cortical zones in aquatic and land Chelonia.
An ultrastructural study is performed with a quantitative analysis of some parameters of the synaptic organization of the superficial plexiform layer of the three basic cortical zones (hippocampal, dorsal and pyriform) of the forebrain in two aquatic and two land Chelonia species. On the basis of our own and literature data it is inferred that all the basic elements of the axo-spino synaptic complexes (dendritic spines--active synaptic zones--nerve endings) exhibit both stability, ensuring the structural durability and reliability of the contacts' functioning, on the one hand, and plasticity responsible for homeostasis and adequate transformations, on the other. Normally, functional shifts in the fine structure of synaptic apparatus are presumably too slight to conceal the specific features of the nerve centres' synaptic organization. This made feasible a comparative study of the structure of the axo-spinal complexes in functionally dissimilar zones, which revealed the following three categories of characters: (1) stable, common of all the Chelonia species under study and characterizing a particular level of the integration of nervous processes, and (2) variable, ecologically-specific and (3) species-specific, ensuring adaptation changes within a given level of interneuronal organization. It has been revealed that ecological differences in the synaptic organization of the cortical zones in the aquatic and land Chelonia are most pronounced in the pyriform and hippocampal cortices, i.e. zones of exclusively and predominantly olfactory projections respectively, and are considerably less pronounced in the dorsal cortex, the zone of predominantly visual afferentation.
D000818:Animals; D001369:Axons / Q000648:ultrastructure*; D002540:Cerebral Cortex / Q000033:anatomy & histology*; D003712:Dendrites / Q000648:ultrastructure*; D004463:Ecology; D006624:Hippocampus / Q000033:anatomy & histology; D008032:Limbic System / Q000033:anatomy & histology; D008854:Microscopy, Electron; D009830:Olfactory Bulb / Q000033:anatomy & histology; D010802:Phylogeny; D013045:Species Specificity; D013569:Synapses / Q000648:ultrastructure*; D013572:Synaptic Vesicles / Q000648:ultrastructure; D014426:Turtles / Q000033:anatomy & histology*