SEROTONIN SIMULATES SOME NEURONAL EFFECTS OF NOCICEPTIVE SENSITIZATION IN HELIX-LUCORUM SNAIL

Serotonin (5-HT) application (10 mcM) onto L-PPl1 neurons of the pleur al ganglia of land snail Helix lucorum produced the synaptic facilitat ion of the neuronal response evoked by sensory stimulation, At the sam e time, it did not change the parameters of the neuronal membrane (res ting potential and membrane excitability), in addition to synaptic fac ilitation, the higher 5-HT concentration (100 mcM) produced an increas e in membrane excitablity and a slight membrane depolarization, The 5- HT effects were modality-dependent: the duration of facilitation of th e response evoked by tactile stimulation of the snail head was about 1 h while that of the response evoked by quinine application (0.3% solu tion) onto the snail lip was 2-3h, The 5-HT effects were site-specific : its application Facilitated only the neuronal responses evoked by ta ctile stimulation of the snail head but not otner body sites. The dyna mics of the electrophysiological effects and the level of bound calciu m were similar in L-PPl1 neurons, The described neuronal effects resem ble those observed after the nociceptive sensitization of these neuron s, The data obtained suggest the 5-HT involvement in the mechanisms of short-term changes and consolidation of long-term plasticity underlyi ng the sensitization in Helix L-PPl1 neurons.