| Abstract: | Differences in the distribution of neurons distinguished by their responses to serotonin and acetylcholine were found in the central nervous system ofHelix pomatia. When applied to the body of the neuron acetylcholine hyperpolarizes the cell more often than it depolarizes it, but depolarization predominates in some regions, e.g., on the dorsal surface of the visceral ganglion. In most cases serotonin stimulates activity and induces depolarization or the appearance of pacemaker oscillations of membrane potential. The oscillogenic effect of serotonin is characteristic, in particular, of white (peptidergic) neurons and the depolarization effect is characteristic of other neurons, including the paired giant metacerebral neurons which contain serotonin in their cytoplasm. Both effects failed to appear in sodium-free solution. A group of neurons in which hyperpolarization was observed in response to serotonin application was found in the visceral ganglion of hibernating snails. The same cells in active snails were stimulated by serotonin. A giant neuron with two variously located cholinergic structures is present on the ventral surface of the ganglion among this group of cells: acetylcholine hyperpolarized it when applied to the cell body but depolarized it when applied to the axon. |
