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Wallis DL, Nash HL. 
“The Action Of Methylated Derivatives Of 5-hydroxytryptamine At Ganglionic Receptors”. 
Neuropharmacology. 1980;19:465-472.
Changes in resting membrane potential induced by 5-HT, methylated derivatives of 5-HT and DMPP were recorded from the rabbit isolated superior cervical ganglion by the sucrose-gap method. Responses were evoked by injections into the superfusion stream to the ganglion of 0.01.2mcmol. Whereas 5-HT and DMPP evoked a relatively brief depolarization followed by an after-hyperpolarization, N,N-dimethyl 5-HT (DM5-HT) and N,N,N-trimethyl 5-HT (TM5-HT) evoked depolarizations of long duration. 5-Hydroxytryptamine and DMPP were approximately equipotent; DM5-HT was 8 times and TM5-HT 70 times more active than 5-MT. Quipezine was a selective antagonist of responses to 5-HT and hexamethonium a selective antagonist of responses to DMPP. Quipazine (I mcM) reduced in amplitude responses to 5-HT by 94/0, those to DM5-HT by 37/O' and.those to TM5-HT by 10%; responses to DMPP increased in amplitude by 42%. When seperfused over the ganglion 5-HT (10 mcM) reduced responses to 5-HT by 56%, those to DM5-HT by 27%, those to TM5-HT by 25%, and those to DMPP by 9%. Hexamethonium (100 AM) reduced responses to DMPP by 84%, those to DM5-HT by 64% and those to TM5-HT by 86%; there was no reduction of responses to 5-HT which were potentiated in 7 of 13 experiments. Thus, during nicotinic receptor blockade responses to 5-HT were often enhanced, while in the presence of quipazine Responses to DMPP were often enhanced. A dual action of DM5-HT and TM5-HT at ganglionic nicotinic and 5-HT receptors is likely. Potentiation of responses mediated via one species of receptor during blockade of the other suggests that 5-HT and nicotinic receptors may be in close association in the membrane.
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