Autumn 2005
O'Shaughnessy's
Journal of the California Cannabis Research Medical
Group
|
Cloning the Receptor
The existence of cannabinoid receptors in the brain —proteins
on the outside of certain cells to which cannabinoids bind, triggering
a cascade of molecular events within the cells— was established
in 1988 by Alynn Howlett (right) and William Devane at St. Louis
University. Researchers were astonished to find that these receptors,
now known
as CB1 receptors, are at least 20 times more prevalent in the brain
than opioid receptors.
A cell contains hundreds of thousands of protein molecules. The cell
membrane is made of fat (lipid). If the cell were as big as a house,
a protein would be as big as, say, a scissors or a doorknob.
A receptor is a protein on the surface of a cell that binds to
something else. The something else is known as a “ligand” or an “agonist.” Neurotransmitters,
hormones, and drugs are smaller than proteins by a factor of 1:5
or 1:10 (they have many fewer atoms than a protein).
The neurotransmitter floats around in the bloodstream and hooks onto
receptors that bind to it specifically. The receptor has contact with
both the outside and the inside of the cell (like a doorknob that,
being twisted on the outside, twists on the inside.) The receptor mediates
between the outside signal and what happens inside the cell.
The job of DNA is to store the directions for how to make all the
proteins in our cells. To clone a receptor means you’ve located and can
copy the gene —the section of DNA— that encodes it.
CB1 receptors are concentrated in the cerebellum and the basal ganglia (regions
responsible for motor control, which may explain why marijuana reportedly eases
muscle spasticity); in the hippocampus (storage of short-term memory); and in
the limbic system (emotional control). Cannabinoids acting through the CB1 receptors
seem to play a role in the processes of reward, cognition, and pain perception,
as well as motor control.
