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Bramwell GJ, Goenye T. 
“Responses of Midbrain Neurones to Micro-Iontophoretically Applied 5-Hydroxy-Tryptamine: Comparison with the Response to Intravenously Administered Lysergic Acid Diethylamide”. 
Neuropharmacology. 1976;15(8):457-61.
Midbrain neurone responses to 5-HT and LSD were studied in rats Experiments were performed on chloral-hydrate (350-400 mg/kg, i.p.) anesthetized male albino 215-350 g rats. Spikes from single midbrain neurones were recorded through the centre barrel of a 7-barrelled glass micropipette or with finely etched tungsten microelectrodes. Neuronal firing was recorded 1-2 min before microcontophoretic drug applications and 10-15 min before i.v. drug treatment and the effects of the drugs then determined. The drugs used included 5-HT, LSD, GABA and glutamate for microlontophoretic studies and LSD for i.v. studies. Some rats were pretreated with p-chlorophenylalanine (PCPA, 200 mg/kg), p-chloro-N-methylamphetamine (10 mg/kg), reserpine (2.5-5.0 mg/kg), pargyline (10.5-11.0 mg/kg), L-tryptophan (1025 mg/kg) or 6-hydroxydopamine (6-OHDA, 200 mcg). Midbrain raphe neurones were more sensitive to the depressant action of microiontophoretically applied 5-HT than other neurones within the midbrain. LSD, given in small i.v. doses (8-20 mcg/kg) or at low microiontophoretic currents,selectively inhibited raphe unit firing within the midbrain. Partial inhibition of non-raphe unit firing was produced by larger i.v. doses (40 mcg/kg) or higher microiontophoretic currents. Pretreat. ment with PCPA, p-chloro-N-methylamphetamine, reserpine, 6-OHDA, pargyline or L-tryptophan did not alter the response of raphe units to i.v. LS:D" Conclusions LSD may act as an agonist on the inhibitory 5-HT receptor as well as an antagonist at excitatory 5-HT receptors.
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