112
7
acting with all of the 5HT receptors, but experimental evidence indicates that its hallucinogenic properties stem from its interaction with the 5HT2a receptor (Appel and Callahan
1989). Very little abuse is observed with mescaline use likely due to bitter taste, nausea
induction and low potency (3000 times less potent then LSD). Nothing is known to date
about the role of mescaline in the plant itself.
7.7 Opioid Receptor: Morphine/Opiates and Opioids
The best-known plant-derived secondary metabolites that affect opioid receptors are the
psychoactive ingredients of opium poppy, morphine and codeine (Weid et  al. 2004).
While opioids is a term to describe all substances that produce morphine-like effects by
interaction with the opioid receptors (. Fig. 7.11) independent of their origin, opiates is
used as a generic term solely for the different alkaloids present in the opium poppy. While
morphine is the main opiate found in opium poppy, it was shown that this plant contains
>30 different alkaloids, including further important pharmacologically active alkaloids
such as noscapine and thebaine (paramorphine).
5HT 2A -Receptor
Serotonine
EN D O G E N O U S :
Mescaline
+
Psilocybin
+
Ergotamine
–
Dimethyltryptamine
+
Lysergide (LSD)
+
HO
N
N
N
N
H
NH
N
H
N
H
NH
NH
N
O
O
O
O
O
O
O
HO
OH
N
N
H
H
O
NH2
NH2
H
N
+
. Fig. 7.10 Examples of natural and synthetic compounds that act as agonists and antagonists of the
dopamine receptor
Chapter 7 · Plant-Derived Drugs Affecting GPRCs