Immediate plasticity of identifiable synapses in the land snails Helix lucorum

The data presented concern synaptic plasticity arising during neuronal resp onse to a single sensory stimulus. The plasticity was studied in identifiab le synapses between sensory and command neurones of Helix lucorum using sim ultaneous intracellular recording. A brief mechanosensory stimulation evoke d a train of spikes in an identifiable visceral sensory neurone. Interspike intervals within the train changed from short (tens ms) to long (s). Each spike elicited an elementary EPSP in an identifiable command neurone. The a mplitude of elementary EPSPs varied during a train of action potentials. In itial high frequency depression was followed by posttetanic potentiation an d subsequent low frequency depression. The result of integration of the thr ee plastic processes has been named immediate plasticity. It has been shown that a compound EPSP elicited in a postsynaptic command neurone by a singl e sensory stimulus depends on the immediate plastic changes of elementary E PSPs.