The Endocannabinoid System

The Endocannabinoid system is a regulatory system within our bodies that affects many necessary biological processes. The Endocannabinoid system is made up of a group of molecules. These molecules are known as “endocannabinoids”. The endocannabinoid system also includes the “cannabinoid receptors” or CB receptors that they bind to.

Cannabinoid Receptors

In 1988, an American scientist Dr. Allyn Howlett PhD. and his graduate student William Devane discovered the presence of cannabinoid receptors in the human brain.

There are two major types of cannabinoid receptors in our bodies, CB1 and CB2. Cannabinoid receptors belong to an essential group of signalling recptors called G-protein coupled receptors. Activation of the extracellular portion of this receptor causes conformational change and initiates intracellular biochemical reactions. The vast number of cannabinoid receptors and their prevalence throughout the body suggests a multitude of promising therapeutic targets.

CB1 Receptors

The Cannabinoid Receptor Type 1., aka “CB1 Receptor” is a G-protein-coupled cannabinoid receptor.Location of the CB1 Receptors

Cannabinoid receptor type-1 (CB1) – CB1 receptors are found primarily in the brain, specifically in the hypothalamus and basal ganglia. CB1 receptors are also found in the cardiovascular and reproductive tissues as well as the gastrointestinal tract.

Mechanism of Action

Activation of CB1 receptors on the membrane of neurons initiate a cascade of reaction affecting perception, movement and memory. With their propensity to modulate neurological excitement CB1 receptors are though to be influential in treating neurological disorders such as Parkinsons and Huntingtons disease. CB1 receptors are highly expressed in areas associated with pain including the periaqueductal gray and the dorsal horn of the spinal chord. There is also mounting evidence to suggest CB1 receptors are essential in modulating the side affects, particularly pain and emesis of chemotherapy.

CB1 receptors are almost absent in the medulla oblongata, the part of the brain stem responsible for respiratory and cardiovascular functions. Thus, there is not the risk of respiratory or cardiovascular failure that can be produced by some drugs.

Expressed at high density throughout the central nervous system, (brain and spinal cord) and at a lower density in the immune cells and within peripheral tissues. The pattern of distribution for the CB1 receptors is heterogenous. This reflects its ability to alter cognition and memory and alter motor function control.

CB1 is activated by Anandamide and arachidonoylglycerol which are Endocannabinoid Neurotransmitters or by phytocannabinoids like that of the compound THC.

CB2 Receptors

CB2 Receptors

Location of the CB2 Receptors

Cannabinoid receptor type-2 (CB2) – CB2 receptors are predominantly found in the immune system, or immune-derived cells with the greatest density in the spleen. Additionally, recent studies suggest that CB2 receptors are also present in the central nervous system.

Mechanism of Action

In immune tissue such as the spleen and tonsils CB2 receptors modulate cytokine release, an essential part of the inflammatory process. In their capacity to mediate inflammation, CB2 receptors have shown significant potential for the treatment of arthritis, crohns disease and colitis. CB2 receptors have been implicated in cell proliferation and differentiation suggesting promising anticancer drug targets.


Signaling Molecules

Endogenous cannabinoid signaling molecules are synthesized on demand from the postsynaptic neuron in order to regulate neurotransmitter release from the presynaptic terminal. This negative feedback function is termed retrograde signaling and characteristic of the endocannabinoid system.


Binds readily to the CB1 receptor. Anandamide is synthesized on demand from the postsynaptic neuron and acts as a retrograde messenger to modulate the release of neurotransmitters form the presynaptic neuron. Additionally anandamide activates the transient receptor potential vanilloid 1 receptor (TRPV1). As a TRPV1 agonist, anandamide is suggested to mediate nerve pain.

2-arachidonoylglycerol (2-AG)

2-AG interacts with both CB1 and CB2 receptors. 2-AG exhibits a lower binding affinity for CB1 compared to anandamide, however higher concentrations of this ligand are present in the brain. 2-AG has been associated with essential biological processes including cell proliferation, immune function, neuroprotection and neuromodulation.

The Endocannabinoid System Medical Terminology Translation:

Endogenous : originating from within or caused by factors within an organism, cell or tissue, or cell.
Signaling molecule : have the ability to cross the plasma membrane where it then can bind to receptors
Post synaptic neuron: a neuron of a cell which an electrical impulse can be transmitted acrosssynaptic cleft by the release of a chemical neurotransmitter from the axon terminal of a presynaptic neuron.
  • Miller-Keane Encyclopedia and Dictionary of Medicine, Nursing, and Allied Health, Seventh Edition. © 2003 by Saunders, an imprint of Elsevier, Inc. All rights reserved.
  • Postsynaptic neuron. (n.d.) Farlex Partner Medical Dictionary. (2012). Retrieved December 17 2015 from Farlex Partner Medical Dictionary © Farlex 2012
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