[The action of the neurotoxins 5,6-dihydroxytryptamine and p-chlorophenylalanine on the electrical activity parameters of the command neurons during long-term sensitization and learning in the snail].

The influence of 5,6-dihydroxytryptamine (5,6-DHT), which selectively destroyed serotonin terminals, and p-chlorphenylalanine, which inhibited serotonin synthesis, was studied on the long-term sensitization (LTS) in a snail. The membrane mechanisms were analyzed by measuring electrical characteristics of command neurons of defensive behavior LPa3, RPa3, LPa2, and RPa2. Snails injected with saline served as an active control. It was shown that the injected drugs inhibited the LTS in certain concentrations. A significant increase was observed in the membrane potential and the threshold of the action potential generation in the command neurons after 5,6-DHT injection in the doses of 20 and 30 mg/kg (in comparison with the active control). Sensitization of snails injected with saline solution led to the LTS and decrease in the membrane and threshold potentials of the command neurons. After the LTS, changes in membrane and threshold potentials in snails injected with 5,6-DHT were negligible in comparison with those injected with 5,6-DHT but without the LTS. Neither the LTS nor subsequent learning resulted in a further decrease in membrane and threshold potentials. Thus, the neurotoxin injection led to an increase in excitability of command neurons and their depolarization, and the LDS did not elicit further excitability increase. Since the shifts of the threshold and membrane potentials were the same, it was concluded that the increase in membrane excitability was induced by the depolarizing shift of the membrane potential.