[Changes in the ultrastructure of frog spinal cord motor neurons following low frequency stimulation of afferent fibers].

Effect of 10 min stimulation on the motoneurones ultrastructure depended on the amplitude of the ventral root biopotentials. In case of low amplitudes dilated endoplasmic spaces, Golgi complex cisterns were seen. Mitochondria were swollen and the number of free ribosomes increased. In the cytoplasm many "whorl--like" structures appeared. In case of high amplitude ventral root biopotentials, alterations were particularly evident in decrease in the ribosomes number, fragmentation of the endoplasmic reticulum. Electron density of the motoneurons was very low. After 25 min stimulation, the number of ribosomes increased in the motoneurons, the Golgi complex proliferated, very large mitochondria appeared. In the dendrites, swollen mitochondria often were adjacent to postsynaptic membranes. Electron density of the motoneurons was very high. The ultrastructural alterations of the motoneurons are supposed to be due to a change of cellular metabolism in the conditions of increased functional activity.