Biomedical Engineering Reference
In-Depth Information
19
Opioid and Cannabinoid
Receptors
Rasmus P. Clausen and Harald S. Hansen
CONTENTS
19.1 Opioid Receptors................................................................................................................. 313
19.1.1 Opioid Receptor Subtypes and Effector Mechanism.......................................... 314
19.1.2 Endogenous Opioid Receptor Ligands................................................................ 314
19.1.3 Nonendogenous Opioid Receptor Ligands.......................................................... 316
19.1.4 Therapeutic Applications and Prospects............................................................. 320
19.2 Cannabinoid Receptors ....................................................................................................... 321
19.2.1 Endocannabinoid System .................................................................................... 321
19.2.2 Cannabinoid Receptor 1...................................................................................... 323
19.2.3 Cannabinoid Receptor 2...................................................................................... 324
19.2.4 Other Cannabinoid Receptors ............................................................................. 324
19.2.5 Therapeutic Use and Potential ............................................................................ 324
19.2.6 FAAH-Inhibitors and Anandamide Uptake Inhibitors ....................................... 326
19.2.7 CB
1
-Receptor Agonist/Antagonist....................................................................... 326
19.2.8 CB
2
-Receptor Agonist/Antagonist ...................................................................... 326
19.2.9 Diacylglycerol Lipase Inhibitors ......................................................................... 327
19.2.10 Monoacylglycerol Lipase Inhibitors.................................................................... 327
Further Readings............................................................................................................................ 328
19.1 OPIOID RECEPTORS
Presently she cast a drug into the wine of which they drank to lull all pain and anger and bring forget-
fulness of every sorrow.
The Odyssey, Homer (ninth century BC)
The history of opioids and its receptors spans several millennia. The i rst evidences of uses of
the seed pods of
Papaver somniferum
dates back to 4200 BC and numerous i ndings and descrip-
tions through out the history witness the use of different parts of this plant in food, anesthesia, and
ritual purposes. Opium (from
opos
, the Greek word for juice) refers to the liquid that appears on
the unripe seed capsule, when it is notched. This liquid contains as much as 16% of morphine, a
compound that was isolated already in 1806 as the major active ingredient in opium (Figure 19.1).
A few years, later codeine was also isolated. Morphine could now be produced and applied in its
pure form for the treatment of pain and as an adjunct to general anesthetics, but it was quickly real-
ized that morphine had the same potential of abuse as opium. In 1898, heroin was synthesized and
claimed to be a safer, more efi cacious, and nonaddicting opiate as were several other analogues
around that time; however, they all proved not to be safer later on. Heroin is an early example of a
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