Abstract
Effects of 5-hydroxytryptamine (5-HT), lysergic acid diethylamide (LSD) and other psychotomimetics upon the potentials induced in thin sections from the superior colliculus of the guinea pig were studied in vitro . The postsynaptic field potential (PSR) evoked by optic tract stimulation was suppressed by 5-HT in concentrations of 10 −7 –10 −6 M . Single neuron discharges induced by optic tract stimulation were also suppressed by 5-HT but spontaneous cell firings were not affected. By higher concentrations of 5-HT (more than 10 −4 M ) PSR was once suppressed but gradually recovered. LSD, lysergic acid ethylamide (LAE) and other related compounds potentiated the 5-HT suppressing action in relatively low concentrations but blocked it in higher ones. Morphine and 2-bromolysergic acid ethylamide (BOL) did not antagonize the 5-HT action. When two shocks were delivered to the optic tract at short intervals and the time course of suppression of the second PSR was studied, it was found that LSD and related compounds accelerated the recovery of the test PSR. Physiological roles of 5-HT in the superior colliculus are discussed.
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