title: The possible site of action of 5-hydroxytryptamine, 6-hydroxytryptamine, tryptamine and dopamine on identified neurons in the central nervous system of the snail, Helix aspersa.
abstract: Intracellular recordings were made from identified neurons in the right parietal ganglion of the snail, Helix aspersa. Cells F 4, 5 and 6 were excited by 5-hydroxytryptamine (5-HT) and inhibited by dopamine while cells in the F 30 area were inhibited by both compounds. Low doses of both tryptamine and 6-HT produced weak excitation of cells F 4, 5 and 6 while higher doses of both compounds inhibit the activity of these cells. In terms of the inhibitory responses, tryptamine and 6-HT are approximately equipotent but between 10 and 100 times less potent than dopamine. d-Tubocurarine reversibly antagonized the excitatory action of 5-HT on cells F 4, 5 and 6 and converted tryptamine and 6-HT excitation to inhibition. In the presence of the antagonist, ergometrine, the dopamine inhibitory response was almost completely abolished while the inhibitory responses to tryptamine and 6-HT were converted to weak excitation. All four agonists inhibited cells in the F 30 area with the following potency ratios: dopamine much greater than tryptamine/6-HT greater than 5-HT. Tubocurarine had no antagonist effects on these responses while ergometrine reduced or blocked all four, often irreversibly. In potassium-free Ringer the inhibitory responses to all four agonists were enhanced. It is concluded that on cells F 4, 5 and 6, low concentrations of tryptamine and 6-HT act on 5-HT receptors while higher concentrations of both agonists act on dopamine receptors. On cells in the F 30 area, 5-HT, 6-HT and tryptamine all act on a dopamine receptor.
mesh_terms: D000818:Animals; D004298:Dopamine / Q000494:pharmacology; D004874:Ergonovine / Q000494:pharmacology; D006372:Helix, Snails / Q000502:physiology*; D007536:Isomerism; D009474:Neurons / Q000187:drug effects*; D018377:Neurotransmitter Agents / Q000494:pharmacology*; D012701:Serotonin / Q000494:pharmacology / Q000031:analogs & derivatives; D014363:Tryptamines / Q000494:pharmacology; D014403:Tubocurarine / Q000494:pharmacology
chemical_list: D018377:Neurotransmitter Agents; D014363:Tryptamines; D012701:Serotonin; C030820:tryptamine; C027803:6-hydroxytryptamine; D004298:Dopamine; D014403:Tubocurarine; D004874:Ergonovine