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![]() ![]() ![]() In this animal, the repeating segmental pattern of the nervous system along with the fact that neurons are relatively few in number, and many are large enough to be recognized allowed the experimental study of the general problem of neuronal specificity. Leeches from two species: Hirudo medicinalis and Haementeria ghilianii, remained the main organism for the study of the question of neuronal self-recognition and self-avoidance. The pioneer studies were performed in the leech, focusing on the central nervous system and developing mechanosensory neurons. The concept of neuronal self-avoidance emerged about 50 years ago. Nervous system of the medicinal leech ( H. Therefore, self-avoidance is necessary for proper neuronal wiring and postnatal development and, together with neuronal tiling (heteroneuronal avoidance), is a crucial spacing mechanism for patterning neural circuits that results in complete and nonredundant innervation of sensory or synaptic space. Neuronal communication requires the coordinated assembly of axons, dendrites, and synapses. Self-avoidance ensures that dendritic territories are covered completely and yet non-redundantly guaranteeing that branches achieve functionally appropriate coverage of input or output territories. This neuronal self-recognition is attained through families of cell recognition molecules which work as individual barcodes, allowing the discrimination of any other nearby branch as either "self" or "non-self". This propriety demands that neurons are able to discriminate "self", which they avoid, from "non-self" branches, with which they coexist. In opposition, branches from different neurons can overlap freely with one another. The arrangements of branches within neuronal arbors are established during development and result in minimal crossing or overlap as they spread over a territory, resulting in the typical fasciculated morphology of neurons (Fig 1). Neuronal self-avoidance, or isoneural avoidance, is an important property of neurons which consists in the tendency of branches ( dendrites and axons) arising from a single soma (also called isoneuronal or sister branches) to turn away from one another. Self-avoidance ensures that there is no overlap of isoneural branches and is at the basis of neuronal circuit assembly. Mechanisms of neural development dependent of neuronal self-recognition. ![]()
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