Cannabinoid Receptors

Cannabinoids exert their effects by interacting with cannabinoid receptors present on the surface of cells in different parts of the central nervous system.

To date, only two types of cannabinoid receptor have been identified, the CB1 receptor which was cloned in 1990 and the CB2 receptor which was cloned in 1993. These two receptors only share 48% amino acid sequence identity, are distributed in different tissues and also have different signalling mechanisms. They also differ in their sensitivity to agonists and antagonists. Studies show that activation of the cannabinoid receptors leads to inhibition of adenylate cyclase, which stops the conversion of ATP to cyclic AMP (cAMP).

A naturally occurring substance within the brain called anandamide that binds to CB1 was detected in 1992. This cannabinoid-like chemical and others that were later discovered, are referred to as endocannabinoids.

Location of the receptors

CB1 receptors

The CB1 receptors are primarily located on nerve cells in the brain, spinal cord, but they are also found in some peripheral organs and tissues such as the spleen, white blood cells, endocrine gland and parts of the reproductive, gastrointestinal and urinary tracts.

In the brain, the CB1 receptors are abundant in the cerebellum, basal ganglia, hippocampus and dorsal primary afferent spinal cord regions, which is why cannabinoids influence functions such as memory processing, pain regulation and motor control. In the brain stem, the concentration of cannabinoids is low, which may be related to why cannabis use is not associated with sudden death due to depressed respiration, for example.

CB2 receptors

The CB2 receptors are mainly found on white blood cells, in the tonsils and in the spleen. The immune cells also express CB1, although there are fewer of them than CB2. In the immune system, one important function of the cannabinoid receptors is the regulation of cytokine release. Stimulation of the CB1 receptor produces marijuana-like effects on the psyche and circulation, while no such effect is seen when the CB2 receptor is activated. Therefore, selective CB2 receptor agonists have become increasingly popular subjects of research for their potential anti-inflammatory and anti-cancer effects.

Reviewed by Sally Robertson, BSc

Further Reading

Last Updated: Jun 2, 2014

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Comments

  1. NotJames Cunningham NotJames Cunningham United States says:

    What psychological behaviors and effects are these cannabinoid receptors responsible for? And what natural functions and behaviors we may experience everyday effected by them?

    • Little Cutting Little Cutting Sweden says:

      It feels like my brain speeding up in activity in the beginning of the high.

      My thinking is flying and gives me lot of ideas in a high tempo.
      After some time I just get calm.

      Most of the times is the thoughts that is flying great feeling thoughts.

      So I think the cannabinoid receptors somehow regulates the frequency of some parts of the brain.

      • Miriam English Miriam English Australia says:

        Because the brain is the organ trying to measure itself, subjective impressions of the speed of thinking can be very wrong. For example if the sense of time is conveyed by the length of time something is kept in short-term memory then impairing short-term memory can make it feel like your thoughts are moving faster when they are really having more difficulty keeping track of previous items in the time stream.

        Time sense is notoriously unreliable. Time yourself counting, trying judge ten seconds when you're excited, and again when you're bored, and again a couple of minutes after you've woken up from sleep. You'll be surprised at how differently time moves, yet in each of those it subjectively feels like it moves the same.

        Watch a wheel spinning, and turn the light illuminating the scene down -- the wheel will seem to speed up.

        Listen to a song while it plays loudly, then turn the volume way down -- the song will seem to speed up.

        Time sense in the brain is very unreliable, and often doesn't mean what you think it does.

The opinions expressed here are the views of the writer and do not necessarily reflect the views and opinions of News-Medical.Net.
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