[Spontaneous EPSPs in Command Helix Lucorum Neurons during Geterosynaptic Potentiation]

To develop the presynaptic mechanism of the short-term plasticity of synaptic transmission the influence of the rhythmical orthodromic stimulation of intestinal nerve on the spontaneous excitatory postsynaptic potentials (EPSPs) have been analyzed in the command neurons of the defensive behavior of land snail Helix lucorum. It was shown early that the tetanic stimulation induced the short-term potentiation of evoked EPSPs. The rhythmical stimulation did not influence the amplitude of spontaneous EPSPs, but considerably increased their number. Discovered augmentation of the frequency of spontaneous EPSPs makes it possible to assume the participation of presynaptic mechanism in the short-term potentiation of synaptic transmission. The presynaptic mechanism can include reduction in the thresh- old of action potentials (APs) generation in the presynaptic neurons, which will lead to an increase in the fraction of spontaneous active neurons and, correspondingly, it will increase the number of spontaneous presynaptic APs.