E.S. Petrova - Senior Research Scientist, Department of General and Special Morphology, FSBSI Institute of Experimental Medicine (St. Petersburg). E-mail:iemmorphol@yandex.ru

In modern neurobiology for identification of neurons in the central and peripheral nervous system at various stages of diffe-rentiation (from neural stem/progenitor cells (NSPC) to mature neurons) various immunohistochemical markers are used. Trans-plantation of embryonic CNS tissues is widely used in experiments concerning the fundamental problems of histogenesis and regeneration of the nervous tissues. Previously it has been shown that tissue grafts and suspension grafts of embryonic rat brain are capable of surviving in transplantation into a damaged nerve in adult animals. Transplanted NSPC continue to differentiate to neurons and gliocytes. However, the neurotransmitter nature of the transplanted cells is poorly understood. The aim of this study was to clarify the possibility of formation of cholinergic neurons in the embryonic rat neocortex allografts developing in the damaged nerve. The study was performed on 10 Wistar rats weighing 200-250 g. The dorsolateral wall of the anterior cerebral vesicle was harvested from embryos at the day 14 of development and transplanted into the lesioned sciatic nerve of adult animals under ether anesthesia. Rats were kept and all experiments were performed in compliance with the - Regulations for studies using experimental animals. - One or two months after surgery the sciatic nerve fragments with transplants were studied. The neurons of the graft were identified by the following immunohistochemical markers: NeuN - for differentiated neurons and choline acetyltransferase (ChAT) ? for cholinergic cells. Motor cortex of rats of corresponding age (P23-53) served as control. It is shown that single cholinergic neurons are located in all layers of the rat neocortex, but mostly in the upper layers. They are usually bipolar and have long processes (70-80 μm) directed perpendicularly to the surface of the brain. Function of the cholinergic neurons in the neocortex is not clear. There are suggestions that they stimulate the relationship of other neurons, contribute to the regulation of cerebral blood flow, and take part in the processes of maturation of neurons in ontogenesis. One or two months after surgery the grafts contain a large number of mature neurons. They are detected by immunohistochemical reaction to the antigen NeuN. The individual ChAT- immunoreactive cells were detected in the graft. However, in contrast to the neurons developing in situ the trasplanted interneurons had short processes. The number of ChAT neurons in the grafts was less than in the controls (neocortex P23-53). At present, achievements in regenerative neurobiology have demonstrated that cellular therapy can have a stimulating effect on the processes of reparative regeneration of the nervous system organs. The experimental elaboration of cellular technologies to stimulate nerve regeneration is carried out actively. There is evidence that the neural stem/progenitor cells, as well as fragments of embryonic rat brain promote the growth of the recipient regenerating axons after transplantation into the damaged nerve or a conduit. In this regard, the study of the fate of the transplanted cells: their differentiation and their neurotransmitter nature takes on particular relevance. The findings: 1. A significant number of NeuN-immunopositive neurons were formed in transplants of embryonic rat neocortex in the damaged nerve 1-2 months after surgery. 2. Some cholinergic (ChAT-immunoreactive) neurons were revealed in the transplants. Thus, a part of progenitor cells retains their characteristic phenotype and the ability to synthesize the neurotransmitter in the changed microenvironment.

 

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