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Montigny C de, Aghajanian GK. 
“Preferential Action of 5-Methoxytryptamine and 5-Methoxydimethyltryptamine on Presynaptic Serotonin Receptors: A Comparative Iontophretic Study with LSD and Serotonin”. 
Neuropharmacology. 1977;16,(12):811-18.
The action of 5-methoxytryptamine (MT); 5-methoxydimethyltryptamine (MD, Regis), LSD and serotonin on presynaptic serotonin receptors in rats was studied. Methods Male albino Charles River rats (220-260 g) were chloral hydrate (400 mg/kg i.p.) anesthetized and recordings were made from the raphe nuclei. In other halothane-anesthetized rats receiving mepivacaine.HCl, anterior pontine sections (cerveau isole) were prepared for recording from postsynaptic areas. MT (0.05 M), MD (0.05 M), LSD (0.001 M) and serotonin (0.04 M) were applied iontophoretically from multibarreled micropipettes and recordings were made from the mid-brain raphe units (presynaptic) and the ventral nucleus of the lateral geniculate body and the basolateral nuclei of the amygdala (postsynaptic). Cells were stained and electrode positions were confirmed histologically. Pre- and postsynaptic efficiencies of drugs were calculated. MD and MT were also given i.v. Results All 4 compounds depressed neuronal firing in the 3 areas. LSD, MD and MT exerted a much more powerful effect on presynaptic neurones whereas serotonin was more active in depressing postsynaptic neurones. The ratios of pre- and postsynaptic efficacies were calculated to be 5.6, 4.3, 1.8 and 0.7 for LSD, MD, MT and serotonin respectively. MD (20 mcg/kg i.v.) rapidly and totally inhibited firing in the dorsal raphe nucleus. MT (20-200 mcg/kg, i.v.) did not affect the firing rate in these neurons. MD (100 mcg/kg i.v.) depressed by 50-60% the firing rate in postsynaptic neurons and was slower acting than on presynaptic neurons. MT may have psychotomimetic properties similar to that reported for MD and LSD.
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