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Gerschenfeld HM, Paupardin Tritsch D. 
“Ionic Mechanisms and Receptor Properties Underlying the Responses of Molluscan Neurones to 5-Hydroxytryptamine. On the Transmitter Function of 5-Hydroxytryptamine at Excitatory and Inhibitory Monosynaptic Junctions.”. 
J Physiol. 1974;243(2):427-481.
Responses of molluscan neurones to iontophoretically-applied 5-hydroxytryptamine (5 - HT) were investigated. Experiments were performed on units in the pert-esophageal ganglion of Helix asperse and the cerebral, buccal or abdominal ganglion of Aplysia californica. Neurones were impaled with double-barrelled microelectrodes filled with 0.6 M K2SO4 10-25 Ml. One barrel was used for recording, the other for the application of pulses to measure membrane resistance and to artificially maintain membrane potential. 5-HT Creatine sulfate was applied from single nicropipettes with a current of 10-100na for 50-1000 msec. Other drugs were dissolved in the bath fluid. 6 Different types of 5-HT response were observed. Type A comprised a 'fast' depolarization which resulted from an increase in Na-conductance while type A'were similar to type A but of longer latency and duration. Type A responses, but not type A', were antagonized by d-tubocurarine (dtc), LSD 25, tryptamine and 7-methoxytryptamine; both responses were blocked by bufotenine. Type B responses were slow hyperpolarizations associated with increased Kit conductance while type C were similar fast responses dependent on increased Cl conductance. Type B responses were antagonized by LSD 25, tryptamine, bufotenine and 5-methoxygramine while type C responses were prevented by dTc, LSD 25, tryptamine, and neostigmine. Responses were depolarizations which reversed with membrane potential -70 mV and were caused by a decrease in K+ conductance. D - Resposes resulted from decreases in the conductance of K+ and Na+ . Two giant cells were located in the Aplysia cerebral ganglion stimulation of which evoked excitatory or inhibitory potentials in cells of the ipsilateral buccal ganglion. Tetraethylammonium (TEA) increased these potentials indicating a monosynaptic path-way. High Ca2 had no effect. Application of 5-HT to the buccal cells elicited A and A' responses,
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