ACTION OF PSYCHOTOGENIC DRUGS ON SINGLE MIDBRAIN RAPHE NEURONS

¹ Department of Psychiatry, Yale University School of Medicine and Connecticut Mental Health Center, New Haven, Connecticut

Because of the previous observation that D-lysergic acid diethylamide (LSD) inhibits raphe neurons, the possible effects on raphe units of other psychotogenic drugs were investigated. In addition to LSD, the following drugs were tested: 1) 2-brom-LSD;2) N N-dimethyltryptamine; 3) mescaline; 4) 2,5-dimethoxy-4-methylamphetamine; 5) scopolamine and atropine; 6) phencyclidine; and 7) various non-psychotogens (e.g., chlorpromazine). There were marked differences in the way the various psychotogenic drugs affected the activity of raphe units. These effects differed according to the structural class of the compounds administered as follows. 1) The drugs containing a N-methylated indolethylamine moiety (i.e., LSD, 2-brom-LSD and N,N-dimethyltryptamine) inhibited all raphe units, although 2-brom-LSD was usually not capable of producing total inhibition. 2) The derivatives of phenethylamine or -methylphenethylamine (i.e., mescaline and 2,5-dimethoxy-4-methylamphetamine) inhibited only those units located in the ventral portion of the dorsal raphe. 3) Atropine, scopolamine and phencyclidine had no effect on raphe unit activity. None of the nonpsychotogenic compounds tested inhibited raphe activity. These results indicate that the indole and phenethylamine psychotogens, which have similar effects on behavior, also have an overlapping although not identical effect on single units in the raphe nuclei. On the other hand, the psychotogenic drugs which differ from the indole and phenethylamine compounds both in chemical structure and behavioral effect do not affect raphe units.

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