Autotomy and self-amputation of nerve processes in tissue culture and in vivo

Abstract

Self-amputation of body appendages, such as severing of the tail by lizards or a leg by long-legged harvestmen (Phalangida), is widespread in nature. This phenomenon is observed in hydroid polyps, actinia, nemertines, annelids, starfishes, mollusks, and crustaceans and is regarded as a physiological protective mechanism [1]. However, the first data on the amputation of neuronal processes [2] were debated, although natural separation of fragments from the nucleus-containing soma and vice versa was described in other cells. The cell fragments separated from megakaryocytes were referred to as platelets [3]. Mammalian erythrocytes separate the nucleus-containing cell fragment and continue to live and function for a long time. Viable cytosomes (cytoplasts) were separated in experiments with the use of cytochalasin in all cells studied [4]. Although self-amputation as a physiological process has not been studied in neurons, we have no doubts that it can be observed in these cells. In this work we studied the autotomy and self-amputation of neurites under normal conditions in cell culture and in vivo. We discovered and analyzed the autotomy of neuronal processes and self-amputation of terminals of nonsynaptic dendrites in the tissue culture and in vivo. It was found that development of both processes is determined by the contractile activity of the processes in combination with adhesion of the terminals to a substrate or to other neurons. We showed that these processes take place continuously during activity of neurons and alternate with protruding growth processes. Self-amputation proceeds by the apocrine mechanism. The data obtained suggest that the dendrites that undergo self-amputation of cytoplasts filled with activated lysosomes have a certain trophic function. The study was performed with the tissue culture of isolated neurons of the pond snail ( Lymnaea stagnalis ). Single neurons were isolated via enzymatic and mechanical processing of the peripharyngeal nerve ring of mature pond snails (for details, see [5]). The cells were cultured for 5‐6 days in a serum-free medium (RPMI-1640 or Eagle’s MEM). The dynamics of regenerating neurons was recorded with an automated microvideoinstallation using time-lapse photography (shooting speed, 1 frame per 10 min) under an inverted phase-contrast microscope (objectives, 20 × , 40 × ; eyepiece, 10 × ). The illustrations are presented as a series of frames from the films. A comparison of the results of in vitro and in vivo studies was performed with the use of Dogel’s type II cells of the enteric plexus of healthy mature cats. The neurons were impregnated according to Bil’shovskii and Gros. The sensor terminals of nonsynaptic dendrites were studied with the use of the conventional electron microscopy.