[A change in the ultrastructure of frog spinal cord and motor neuron synapses during prolonged activation].

Motoneuron axosomatic synapses (AS) were shown to be larger than axodendritic (AD) synapses under anaesthesia. A 10 minute-long electrical stimulation both by low and high frequency caused enlargement of AS and AD synapses, it being the more pronounced the higher was the activation frequency. In all cases changes the AS synapses were more marked than those of AD synapses. On the bases of morphological and physiological data it was concluded that the changes of the synapse dimentions did not affect the synaptic transmission.