Findings of light optical and electron microscopy studies on formation of multinuclear neurons in gastrointestinal tract myenteric plexus in mammals affected by extreme factors (vagotomy, modelling of portal hypertension. Hyperbaric oxygenation and hypergravitation) were presented. A model for original transformation of multinuclear neuron as a mechanism of new nerve cells formation in the course of the organism compensatory-adaptive reaction to extreme action was obtained.