ABSTRACT
The ultrastructure and protein content of goldfish Mauthner cells (M-cells) at different functional states induced by natural vestibular stimulations were studied. 2-h stimulation, usually causing a fatiguing of the fishes, was found to be accompanied by ultrastructural changes within M-cells and a decreased content of cytoskeletal proteins. After training by short stimulations resulting in a long-term adaptation of the fishes, the ultrastructure and protein content of M-cells could not be distinguished qualitatively and quantitatively from those of non-adapted fishes. When the adapted fishes were stimulated for 2 h the content of a 70-kDa protein was found to be increased. In addition, the content of a 42-kDa protein, obviously actin, was elevated in this case. Correspondingly, electron microscopic analysis demonstrated a significantly increased resistance of the cytoskeleton to fatiguing stimulation. The data obtained indicate that the neural cytoskeleton is a central target of fatiguing stimulation. We suppose that the 70-kDa protein is responsible for the adaptive properties of the cytoskeleton. This protein is assumed to be identical with one of the so-called heat-shock proteins of non-neural cells which have the same electrophoretic mobility and are also able to protect the cytoskeleton under stress conditions.
