110
7
7.5 Dopamine Receptors: Cocaine and L-DOPA
As presented above (see 7 Sect. 5.5 in Chap. 5), dopamine has a very important function
for the reward system in the human brain, and therefore all drugs that enhance dopamine
signalling may have an exhilarating effect on humans. There is no secondary metabolite
known to directly interact with the dopamine receptor (. Fig. 7.9), but compounds such
as cocaine can enrich dopamine concentration by inhibition of the dopamine transporter
(Ritz et al. 1987). These inhibitors also affect the transporters for serotonin and norepinephrine leading to multiple effects.
Cocaine is a tropane alkaloid exclusively found in coca plants (Erythroxylum spp.).
While found in the leaves of many species of Erythroxylum, larger amounts of cocaine are
only present in two cultured varieties. Cocaine concentration can vary with environmental conditions and age, but synthesis seems to occur throughout the lifetime of the plant
(Rivier 1981). The most likely role of cocaine is protection against pathogens and herbivores since coca plants in the field are unusually pest free with herbivore attack observed
only rarely (Plowman and Weil 1979). It was shown that spraying tomato plants with
cocaine caused rearing, tremors and walk-off behaviour in Manduca sexta larvae. Higher
concentrations led to the death of the larvae after 24–48 h (Nathanson et al. 1993). Cocaine
furthermore affected the hatching of larvae if eggs were exposed, and it was also shown to
be effective against mosquito larvae.
Legumes plants such as velvet bean (Mucuna pruriens) or broad bean (Vicia faba) were
shown to contain L-3,4-dihydroxyphenylalanine (L-DOPA), a precursor of adrenalin,
noradrenalin and dopamine. It occurs in plants as an intermediate in the synthesis of
HO
NH 2
HO
N
N
N
NH
CI
CI
HO
N
HO
OH
H
N
O
F
–
+
–
Dopamine receptor
Dopamine
EN D O G E N O U S :
Haloperidol
(D2)
Apomorphine
(D1/2)
Clozapine
(D3/4)
. Fig. 7.9 Examples of synthetic compounds that act as agonists and antagonists of the dopamine
receptor
Chapter 7 · Plant-Derived Drugs Affecting GPRCs
7
7.5 Dopamine Receptors: Cocaine and L-DOPA
As presented above (see 7 Sect. 5.5 in Chap. 5), dopamine has a very important function
for the reward system in the human brain, and therefore all drugs that enhance dopamine
signalling may have an exhilarating effect on humans. There is no secondary metabolite
known to directly interact with the dopamine receptor (. Fig. 7.9), but compounds such
as cocaine can enrich dopamine concentration by inhibition of the dopamine transporter
(Ritz et al. 1987). These inhibitors also affect the transporters for serotonin and norepinephrine leading to multiple effects.
Cocaine is a tropane alkaloid exclusively found in coca plants (Erythroxylum spp.).
While found in the leaves of many species of Erythroxylum, larger amounts of cocaine are
only present in two cultured varieties. Cocaine concentration can vary with environmental conditions and age, but synthesis seems to occur throughout the lifetime of the plant
(Rivier 1981). The most likely role of cocaine is protection against pathogens and herbivores since coca plants in the field are unusually pest free with herbivore attack observed
only rarely (Plowman and Weil 1979). It was shown that spraying tomato plants with
cocaine caused rearing, tremors and walk-off behaviour in Manduca sexta larvae. Higher
concentrations led to the death of the larvae after 24–48 h (Nathanson et al. 1993). Cocaine
furthermore affected the hatching of larvae if eggs were exposed, and it was also shown to
be effective against mosquito larvae.
Legumes plants such as velvet bean (Mucuna pruriens) or broad bean (Vicia faba) were
shown to contain L-3,4-dihydroxyphenylalanine (L-DOPA), a precursor of adrenalin,
noradrenalin and dopamine. It occurs in plants as an intermediate in the synthesis of
HO
NH 2
HO
N
N
N
NH
CI
CI
HO
N
HO
OH
H
N
O
F
–
+
–
Dopamine receptor
Dopamine
EN D O G E N O U S :
Haloperidol
(D2)
Apomorphine
(D1/2)
Clozapine
(D3/4)
. Fig. 7.9 Examples of synthetic compounds that act as agonists and antagonists of the dopamine
receptor
Chapter 7 · Plant-Derived Drugs Affecting GPRCs