Hallucinogenic drug interactions at human brain 5-HT2 receptors: implications for treating LSD-induced hallucinogenesis.
It has been shown that the hallucinogenic potencies of LSD, the phenylisopropylamines, such as DOB (4-bromo-2,5-dimethoxyphenylisopropylamine) and DOI (4-iodo-2,5-dimethoxyphenylisopropylamine), and the indolealkylamines, such as DMT (dimethyltryptamine) and 5-OMe-DMT (5-methoxy-dimethyltryptamine), strongly correlate with their in vitro 5-HT2 receptor binding affinities in rat cortical homogenates. In order to ascertain if this correlation applies to human 5-HT2 receptors as well, we examined the affinities of 13 psychoactive compounds at 3H-ketanserin-labelled 5-HT2 receptors in human cortical samples. Both radioligand binding and autoradiographical procedures were used. As in rat brain, d-LSD was the most potent displacer of 3H-ketanserin specific binding with a Ki of 0.9 nM. The phenylisopropylamine DOI also displayed high affinity (Ki of 6 nM). Stereospecific interactions were found with DOB; (-) DOB had a Ki of 17 nM while (+) DOB had a Ki of 55 nM. The behaviorally active compound DOM (4-methyl-2,5-phenylisopropylamine) had an affinity of 162 nM while its behaviorally less active congener iso-DOM had an affinity of 6299 nM. The indolealkylamines 5-OMe-DMT and DMT competed with moderate affinities (207 and 462 nM, respectively). In general, Hill coefficients were significantly less than unity which is consistent with an agonist interaction with 5-HT2 receptors. MDMA, a substituted amphetamine analog was inactive with a Ki of greater than 10 microM. A strong correlation was found for the hallucinogen affinities and human hallucinogenic potencies (r = 0.97). Also, human and rat brain 5-HT2 receptor affinities were strongly correlated (r = 0.99). These results strongly support the hypothesis that the hallucinogenic effects of these drugs in humans are mediated in whole or in part via 5-HT2 receptors. Furthermore, these studies imply that treatment with 5-HT2 receptor antagonists may be effective in reversing the hallucinogenic effects caused by the ingestion of LSD and LSD-like drugs.
Sadzot
B
B
Department of Neuroscience, Johns Hopkins University School of Medicine, Baltimore, MD 21205.
Baraban
J M
JM
Glennon
R A
RA
Lyon
R A
RA
Leonhardt
S
S
Jan
C R
CR
Titeler
M
M
D000818:Animals; D001667:Binding, Competitive / Q000187:drug effects; D002540:Cerebral Cortex / Q000033:anatomy & histology / Q000378:metabolism; D006212:Hallucinations / Q000139:chemically induced / Q000188:drug therapy*; D006213:Hallucinogens / Q000378:metabolism* / Q000494:pharmacology; D006801:Humans; D066298:In Vitro Techniques; D007650:Ketanserin / Q000494:pharmacology; D008238:Lysergic Acid Diethylamide / Q000494:pharmacology*; D051381:Rats; D011985:Receptors, Serotonin / Q000187:drug effects / Q000378:metabolism*
D006213:Hallucinogens; D011985:Receptors, Serotonin; D008238:Lysergic Acid Diethylamide; D007650:Ketanserin