OBJECTIVES: The aim of the study was to describe the development of self-mutilation after extensive dorsal rhizotomy of the brachial plexus performed during early ontogeny in rats. SETTINGS AND DESIGN: The rhizotomy was performed in three groups of rats according to the central nervous system maturation: infant, young, and adult. After the surgery the occurrence of self-mutilation behavior was compared. Rats from the infant group and non-mutilating deafferentated rats from the adult group underwent extracellular recordings from intralaminar thalamic neurons. Interspikes intervals of the records were compared by means of chaodynamic methods. RESULTS: In the infant group self-mutilation did not develop at all. Among the young group self-mutilation developed in 40% of rats and consisted of superficial wounds in all cases. In adult self-mutilation appeared in 80% rats and consisted of both superficial wounds (75%) and amputation (25%). In the newborn group and the deafferentated adult group without any signs of self-mutilation means of the parameters were not significantly different and were significantly lower than those of intact adult rats. MAIN FINDINGS: 1. Self-mutilation does not develop after the rhizotomy in the infant rats. 2. Neurons behave in chaotic way in adult as well as in young animals. 3. Chaodynamic parameters do not differ between infant and adult rats without any signs of self-mutilation. CONCLUSIONS: The results suggest that development of self-mutilation behavior in rats strongly depends on the ontogenetical period of nervous system injury, and that mature nervous system is required for the development of described pathological behavior.

Department of Normal Pathological and Clinical Physiology Charles University 3rd Faculty of Medicine Prague Czech Republic