[Changes in the acetylcholine responses of perfused neurons of Limnaea stagnalis during internal and external exposure of the cell].

The modifying effect of extra- and intracellular administration of serotonin on inward currents generated by the cell at extracellular application of acetylcholine was studied. The study was made on nonidentified isolated neurons of the fresh water mollusc Lymnaea stagnalis using the voltage-clamp and intracellular perfusion methods. In roughly a half of the studied cells serotonin being added intra- and extracellularly produced a decrease in the response to acetylcholine. In the other half of neurons serotonin being added intracellularly increased the acetylcholine response, but applied extracellularly showed the opposite effect: it decreased the magnitude of inward acetylcholine currents. The blocker of serotonin receptors, cyproheptadine, blocks the enhancing effect of serotonin on the intracellular addition of the mediator, but mimics the inhibitory effect of serotonin on acetylcholine response. The data obtained on the neurons of molluscs suggest the existence of intracellular receptors of serotonin one whose possible functions is the regulation of sensitivity of the cell surface cholinoreceptors.