Effects of serotonin levels on postsynaptically induced potentiation of snail neuron responses

Studies on identified neurons in the common snail were performed to investigate potentiation of EPSP arising after intracellular tetanization of the post-synaptic neuron. These experiments showed that high-frequency intracellular tetanization of a command neuron leads to biphasic long-term increases in the amplitude of synaptic responses to test stimulation. The role of serotonin in forming potentiation was studied. It was suggested that the presence of particular serotonin concentrations in the intercellular fluid is required for forming the second phase of the increase in synaptic responses, while the first (transient) phase is insensitive to CNS serotonin levels.