Journal of Neuroscience, Vol 1, 1148-1154, Copyright © 1981 by Society for Neuroscience
Serotonin autoreceptors on dorsal raphe neurons: structure-activity relationships of tryptamine analogs
MA Rogawaski and GK Aghajanian
A series of indole-ethylamines were tested for their ability to suppress
the spontaneous firing of single dorsal raphe serotonergic neurons in the
rat. The compounds were all derivatives of either tryptamine or
N,N-dimethyltryptamine possessing hydroxy or methoxy substituents on the
benzene ring portion of the indole nucleus. Their activity was assessed
using quantitative microiontophoresis or following systemic (intravenous)
administration. The serotonin autoreceptor or so-called "S2 receptor"
mediating the inhibition of raphe serotonergic neurons was found to exhibit
a high degree of structural specificity among the closely related
tryptamine analogs. The following structure-activity rules were
demonstrated: (1) for either hydroxy or methoxy derivatives, the relative
favorability of the ring positions conforms to the series 5 much greater
than 4 greater than 6; (2) methoxy derivatives are more sensitive to a
shift of the ring substituent from the 5- to the 4- or 6-positions than are
hydroxy compounds; and (3) activity is enhanced by N,N-dimethylation.
Furthermore, addition of a methyl group at the 7-position of 5-methoxy-
N,N-dimethyltryptamine markedly reduces the activity of this potent
agonist. Of the radioligands which label brain serotonin receptors, the
pharmacological characteristics of D-[3H]lysergic acid diethylamide binding
best correspond to those displayed by the S2 receptor as determined in the
present physiological analysis, although sufficient data are not yet
available to make a complete comparison.