APOPTOSIS AFTER INJURIES IN THE CEREBELLUM OF ADULT TELEOST FISH

In contrast to mammals, all teleost fish examined thus far exhibit an enormous potential to regenerate not only neuronal processes (axonal r egeneration), but even whole neurons (neuronal regeneration) after inj uries in the central nervous system. By application of lesions to one subdivision of the cerebellum, the corpus cerebelli, the role of apopt osis in neuronal regeneration was examined in the gymnotiform fish, Ap teronotus leptorhynchus. Apoptotic cells were identified by examinatio n of cryosections with the terminal deoxynucleotidyl transferase-media ted dUTP-biotin nick end labelling (TUNEL) reaction, an in situ techni que employed for detection of nuclear DNA fragmentation. Additional ev idence for the apoptotic nature of dying cells was obtained through an alysis of morphologies displayed at both the light microscopic and the ultrastructural level. The first TUNEL-positive cells at the site of the lesion appeared as rapidly as 5 min following mechanical damage of the tissue. Thirty minutes after stab wound lesion, their number reac hed maximum levels. Starting with 2 days of postlesioning survival tim e, a gradual decline in the number of TUNEL-positive cells was evident , until this: process reached background levels 20 days after the lesi on. We hypothesize that apoptosis is used in A. leptorhynchus as an ef ficient mechanism for the removal of cells damaged through injury in t he central nervous system. Since apoptosis is not accompanied by the s ide-effects known from necrosis (which is predominant after injuries i n the mammalian central nervous system), this ''clean'' type of cell d eath may, at least partially, explain the tremendous regenerative capa bility of teleosts. (C) 1998 Academic Press.