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Abstract
Microinjections of LSD (0.05 microgram), mescaline (0.5 microgram) and serotonin (10
microgram) into the medial raphe nucleus of rats resulted in a strong potentiation
of apomorphine (1 mg/kg i.p.)-induced hypermotility. The potentiating effect of LSD
or serotonin was suppressed by simultaneous injections of methysergide (0.05 microgram)
or cyproheptadine (0.05 microgram) into the medial raphe nucleus. The same doses of
LSD injected into the dorsal raphe nucleus and of LSD and mescaline injected into
the nucleus accumbens failed to influence locomotor activity, whereas injections of
higher doses of LSD and mescaline into the nucleus accumbens inhibited spontaneous
and apomorphine-stimulated locomotor activity. It is concluded that the potentiating
effect of systemically administered low doses of hallucinogens was triggered by preferential
actions on the serotonergic system in the medial raphe nucleus.