Degree of Specificity of the Synaptic Contacts during Neurotransplantation

Transplantation of immature neural tissue is a promising biotechnological approach for restoring damaged brain circuitry. The success of transplantation therapy depends on implementation of the genetic program of differentiation of donor neural progenitors and the accuracy of neural connections both in the grafts themselves and in the recipient’s brain. The aim of this work was to study the degree of specificity of synaptic connections during transplantation of the hippocampal formation into the neocortex of rats. Electron microscopy was used in this study, and after analysis of the obtained images it was found that specific forms of synapses, which were topographically correctly located on the neuronal soma-dendritic surface, were predominantly differentiated in the grafts. The axons of the grafted neurons growing into the recipient's brain formed synaptic connections with neurons that were unusual for them normally. During the formation of nonspecific axonal connections, they modified the composition and distribution of neurotransmitter vesicles in presynaptic terminals, and also induced structural and chemical reorganization in postsynaptic dendrites.