[Morpho-functional changes in mauthner neurons of goldfish adapted to prolonged orthodromic stimulation of acoustic nerve in vitro].

In newly-hatched goldfish the adapted state was developed using repeated short-term stimulation of the vestibular apparatus. It differed from the non-adapted state by the absence of fatigue during the turns of fishes produced by unilateral tail fin flicks in ring channel. Electrophysiological study of Mauthner neurons (MN) in adapted goldfish using the slices of medulla oblongata incubated in vitro, has shown the preservation of the amplitude of the extracellular responses after prolonged orthodromic electric stimulation of acoustic nerve, which suppressed the responses of non-adapted MN. Thus, the resistance against fatigue has developed also at the level of MN. Using electron microscopy it was demonstrated that adapted MN following the prolonged electric stimulation in vitro were characterized by the resistance of specialized desmosome-like contacts, similar to what was earlier observed in these neurons in vivo. The data obtained suggest that indirect evaluation of MN functional state in goldfish by counting the number of turns performed by it in narrow ring channel, corresponds to the direct morpho-functional assessment of MN state. This form of innate behavior of freely moving fish seems to be the result of MN excitation.