Stabilization of motor asymmetry in the goldfish under the influence of optokinetic stimulation

Abstract

Adaptation as a memory model appears, at the cellular level, as an increase in the resistivity of neurons to fatigue under the influence of repetitive natural training stimulation. Selective induction of adaptational changes in separate compartments of one and the same neuron can also serve as an important instrument for identification of the roles of these compartments in the integrative function of the individual neuron. Mauthner neurons (MNs) of fishes (the goldfish in particular) possess a clearly differentiated soma and two dendrites, lateral and ventral ones. The soma and lateral dendrite of each MN receive afferentation from the ipsilateral vestibular apparatus; at present, the functional and morphological aspects of selective adaptational modifications induced in these compartments by adequate vestibular stimulation have been examined in detail. As to the ventral MN dendrite receiving visual afferentation from the contralateral eye via the ipsilateral tectum, it remained impossible until now to realize the respective approach. We found that training sessions of visual optokinetic stimulation performed in certain modes provide selective activation of one MN through its ventral dendrite and increase the resistivity of this cell to fatiguing stimulation. Therefore, we first demonstrated the possibility of adaptational changes in an individual ventral dendrite of the MN. If fishes were preliminarily adapted with respect to vestibular stimulation, and the resistivity of the soma and lateral dendrite was selectively increased, the resistivity to fatiguing visual test stimulation also increased. On the other hand, if fishes were preliminarily adapted with respect to visual stimulation, the resistivity to fatiguing vestibular stimulation also increased. The observed increase in the resistivity of MNs of fishes adapted due to sensory stimulation of one afferent input with respect to sensory stimulation of other sensory input, as well as an increase in the resistivity to sensory stimulation of one modality, probably show that the mechanism of increase in the resistivity is the same in both cases.