WHY YOUR BRAIN IS PRIMED FOR A HIGH

THE function of brain receptors to which cannabinoid drugs bind is at
last being uncovered. Neuroscientists have shown that a brain chemical
that binds to the receptors modifies the effect of the
neurotransmitter dopamine and so helps us to control our movements.

The chemical, called anandamide, is released from a brain structure
called the striatum. This also makes dopamine, and researchers led by
Daniele Piomelli of the University of California at Irvine have shown
that the two are released simultaneously.

To find out why, Piomelli and his colleagues gave mice a chemical
known to block the brain's cannabinoid receptors. At the sama time,
they sirnulated a surge in dopamine levels using a drug called
quinpirole, which mimics the neurotransmitter. The mice developed
nervous ticks and poorly controlled movements (Nature Neuroscience,
vol 2, p 358).

These symptoms are similar to those of Tourette's syndrome and
Parkinson's disease, which are thought to be linked to problems in the
dopamine system. The involvement of anandamide may explain why some
people claim marijuana can help ease the symptoms of Parkinson's. The
discovery coutd also lead to the development of drugs to treat the
disease by slowing the breakdown of anandamide.

Leslie Iversen of Oxford University describes the new study as a
landmark". But Piomelli suspects the brain's caninabinoid system has
several other functions still waiting to be discovered.