Serotonin simulates some neuronal effects of nociceptive sensitization in helix lucorum snail

Serotonin (5-HT) application (10 mcM) onto L-PPl1 neurons of the pleural ganglia of land snail Helix lucorum produced the synaptic facilitation of the neuronal response evoked by sensory stimulation. At the same time, it did not change the parameters of the neuronal membrane (resting potential and membrane excitability). In addition to synaptic facilitation, the higher 5-HT concentration (100 mcM) produced an increase in membrane excitablity and a slight membrane depolarization. The 5-HT effects were modality-dependent: the duration of facilitation of the response evoked by tactile stimulation of the snail head was about 1 h while that of the response evoked by quinine application (0.3% solution) onto the snail lip was 2-3h. The 5-HT effects were site-specific: its application facilitated only the neuronal responses evoked by tactile stimulation of the snail head but not other body sites. The dynamics of the electrophysiological effects and the level of bound calcium were similar in L-PPl1 neurons. The described neuronal effects resemble those observed after the nociceptive sensitization of these neurons. The data obtained suggest the 5-HT involvement in the mechanisms of short-term changes and consolidation of long-term plasticity underlying the sensitization in Helix L-PPl1 neurons.