PHARMACOLOGICAL STUDIES ON HELIX NEURON OCTOPAMINE RECEPTORS

1. Intracellular recordings have been made from identified neurons in the suboesophageal ganglionic mass of the snail, Helix aspersa. Four cells were found which were inhibited by octopamine and one cell which was excited. The responses of these cells to dopamine, noradrenaline, 5-hydroxytryptamine, glutamic acid and acetylcholine were determined. 2. A structure-activity study was performed on two cells, cell F89 which was inhibited by octopamine, dopamine and noradrenaline and cell E26 which was excited by octopamine but inhibited by both dopamine and noradrenaline. The results suggest evidence for a specific octopamine receptor. 3. A series of compounds were tested for potential blocking activity against octopamine, dopamine and noradrenaline. Phentolamine, 2 × 10-7 M, blocked the action of octopamine and noradrenaline on cell 89 without affecting that of dopamine. On cell E26 phentolamine, 2 × 10-7 M, blocked the excitatory action of octopamine without any effect on dopamine and noradrenaline inhibition. Fluphenazine, 2 × 10-7 M, blocked the action of dopamine and noradrenaline without affecting the octopamine response of either cell. 4. The present data present further evidence for a specific octopamine receptor on Helix neurons. The requirements for optimal activity are: a hydroxyl group on the para position of the benzene ring, an ethylamine side chain with a hydroxyl group on the beta carbon, substitution of no more than one methyl group on the terminal nitrogen. © 1979.