Cannabinoids and Their Receptors


Exogenous cannabinoids are ∼60 molecules with a similar structural motif found in marijuana and hashish. Some of these are psychoactive – the chief being Δ9‐tetrahydrocannabinol (Δ9‐THC) – and have been found to exert their psychoactive effects via receptors in the body. The human body makes endogenous cannabinoids that are structurally distinct from exogenous cannabinoids. This combination of endocannabinoids (eCBs) and receptors form an important endogenous signalling system with roles in numerous aspects of brain function including memory, motor control, appetite, nausea and pain.

Keywords: cannabinoid; CB1; CB2; anandamide; 2‐AG; marijuana

Figure 1.

Structures of three cannabinoids. Chemical structures of Δ9‐tetrahydrocannabinol (Δ9‐THC) the chief psychoactive ingredient of marijuana and hashish; WIN‐55212‐2 a commonly used synthetic agonist for the cannabinoid CB1 receptor; 2‐arachidonyl glycerol (2‐AG), a putative endogenous cannabinoid. Note that although all cannabinoids are lipophilic, their structures can be quite different. Δ9‐THC does not resemble putative endogenous cannabinoids 2‐AG or anandamide.

Figure 2.

Depolarization induced suppression of excitation (DSE). Schematic of pre‐ (top) and post‐synaptic terminals. Standard action potential‐induced neurotransmitter release (using glutamate as example) occurs via activation of calcium channels linked to transmitter‐filled vesicles which fuse with the membrane to release their contents. Glutamate then acts on assorted post‐synaptic glutamate receptors. In contrast, DSE involves depolarization‐induced post‐synaptic production of endocannabinoids (eCBs) (anandamide or 2‐AG – the latter shown as example). A favoured mechanism involves activation of the enzyme DAG lipase, converting diacylglycerol (DAG) into 2‐AG. Rather than being released from vesicles, lipophilic eCBs appear to cross the membrane via facilitated diffusion across a transporter. The mechanism of subsequent transport across the synapse is unknown but may involve chaperone proteins. Activation of pre‐synaptic CB1 receptors inhibits action potential‐induced transmitter release by inhibiting Ca2+ channels.


Further Reading

Onaivi E, Sugiura T and Di Marzo V (eds) (2005) Endocannabinoids: The Brain and Body's Marijuana and Beyond. London, UK: CRC Press/Taylor & Francis Group. 584pp.

Iversen L (2001) The Science of Marijuana. Oxford: Oxford University Press. 304pp.

Piomelli P (2003) The molecular logic of endocannabinoid signalling. Nature Reviews Neuroscience 4(11): 873–884.

Alger B and Nicoll R (2004) The brain' own marijuana. Scientific American 291(6): 68–75.

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Straiker, Alex(Dec 2007) Cannabinoids and Their Receptors. In: eLS. John Wiley & Sons Ltd, Chichester. [doi: 10.1002/9780470015902.a0000030]