Hyperforin, the main
antidepressant constituent of Hypericum perforatum, influences the extracellular concentrations of transmitters in vitro and in vivo. In vivo experiments have shown that
hyperforin enhances the extracellular concentrations of
dopamine,
norepinephrine,
serotonin and
glutamate in the locus coeruleus.
Hyperforin-free Hypericum extract also elevates the extracellular concentrations of
dopamine and
norepinephrine in the locus coeruleus, but, in contrast to
hyperforin, the extracellular concentration of
serotonin is diminished. The differing profiles of
hyperforin and
hyperforin-free Hypericum extract on the extracellular transmitter concentrations point to the presence of an additional biologically active compound in Hypericum perforatum. Inescapable
shock increases the release of monoamines and several
amino acids, as well as motility, blood pressure and heart rate. Conditioned fear, similar to
hyperforin-free Hypericum extract, decreases the release of
serotonin in the locus coeruleus. Conditioned fear also leads to
tachycardia. The latter finding shows that telemetric heart rate recording is a good index for conditioned fear. In vivo findings confirm the idea that the anti-depressive properties of Hypericum extract and
hyperforin result from increases in extracellular
neurotransmitter concentrations. Since
hyperforin-free extract, like conditioned fear, reduces the extracellular concentration of
serotonin,
hyperforin may be more beneficial than Hypericum extract in the treatment of
depressive disorders.