Zeitschrift fiir Zellforschung 59, 851--856 (1963) Instituto de InvestigaciSn de Ciencias BiolSgicas, Montevideo - - Uruguay ELECTRON MICROSCOPIC OBSERVATIONS ON THE REACTIONAL CHANGES OCCURRING IN INSECT NERVE FIBERS AFTER TRANSECTION* By J. MEL~ED and O. TRUJILLo-CENSz With 3 Figures in the Text (Received December 3rd, 1962) Introduction The morphological changes occurring in the vertebrate nerve fiber after tran- section, crushing, or permanent constriction have been studied extensively by light microscopists. These studies have demonstrated that the regenerative process occurs at the proximal stump of the transected nerve fibers and that the distal segments suffer irreversible degenerative changes. The most complete morphological analysis of nerve regeneration and degeneration was undoubtedly made by S. R~oN y CAJAL (1928). Present knowledge in this field is mainly based upon CAJAL'S concepts which have remained practically unchanged since then. The possibility of exploring neurons and their processes with the electron microscope has stimulated new investigations on the regenerative and degenera- tive phenomena in nerves. ESTABLE, ACOSTA and SOTELO (1957) published the first electron microscopic study on the process of nerve regeneration. Another paper reporting electron microscopic observations on regenerating and degenerat- ing nerves of the rat was published by GHMSTEDT and WOHLFART (1960). The accurate study by BODENSTEIN (1958) in the roach Periplaneta americana demonstrated the capacity of regeneration existing in invertebrate nerves. With the exception of the study by HEss (1960) concerning degenerative changes in the nerve fibers of the abdominal cord of the cockroach, no comprehensive ultra- structural investigations seems, nervertheless, to have been undertaken. This paper deals with the reactional changes observed in nerve fibers of a species of Orthoptera after surgical transection of the interganglionic connectives. The description of the electron microscopic aspect of transccted fibers will be preceeded by a short report on the fine structure of normal interganglionic connectives. It is important to realize that the interganglionic connectives cannot be homologized with peripheral nerves of vertebrates; actually, they arc more similar to the "commissures" existing in the central nervous system of verte- brates. Transection of two interganglionic connectives results in four stumps each containing fiber segments connected with their cell bodies, as well as fibers separated from them. Material and Methods Fully developed females of Laplatacris dispar (REn~), Orthoptera-Acrididae, were used in this study. The animals were immobilized under a dissecting microscope and a deep sec- * This research was supported by the United States Air Force under Contract NoAF 49 (638) 585 and Grant Af 61--64, monitored by the Air Force Office of Scientific Research, Air Force l~esearch Division of the Air Research and Development Command. Z. Zellforsch., Bd. 59 56