Interaction of serotonin and leu-enkephalin on the habituating central neurons of Helix pomatia L. in situ and in vitro.

1. Habituating neurons (a, b and c) of Helix pomatia reacted to the serotonin (10(-5)-10(-4)M) with depolarization evoking oscillatory waves and burst firing at the range of -35 to -55 MP values. 2. Isolated habituating cells were hyperpolarized by serotonin and failed to generate membrane oscillation or bursting pattern. 3. Only the isolated habituating neurons reacted to the application of leu-enkephalin (10(-5)-10(-4)M) by depolarization. 4. Neither membrane oscillation nor burst firing were evoked by leu-enkephalin. 5. On the cells a, b and c leu-enkephalin modulated the serotonin effect through cyclic 3',5'-AMP system both in situ and in vitro. 6. The membrane oscillation and burst firing of the habituating cells are connected to the regulation of various rhythmic processes including pneumostoma movements.