Marijuana, meanwhile, could be disrupting the system by acting in a nondiscriminatory manner, says Wilson.

The researchers, conducting their study in rats, discovered that cannabinoid is the signaling molecule within a unique system of communication that is activated intermittently between two of the brain's most ubiquitous nerve cells -- neurons containing the inhibitory neurotransmitter GABA, and neurons containing the excitatory neurotransmitter glutamate. The modulation of inhibitory and excitatory signals leads to the regulation of excitation and inhibition within clusters of neurons that is the basis for all action and thought.

Normally, brain cells containing the inhibitory neurotransmitter GABA release their signal and it diffuses across a synapse and on to receptors on cells containing the excitatory neurotransmitter glutamate, thereby dampening excitatory behavior. This orderly flow of information from pre-synaptic to post-synaptic cell is the classical form of communication in the nervous system.

But, of interest to the researchers, when excitatory glutamate neurons are highly charged electrically, they release a molecular signal that moves backwards, across the synapse, to a subset of inhibitory GABAergic neurons that have a receptor known as CB1. The event briefly inhibits the release of inhibitory GABA neurotransmitters, thus allowing the excitatory neurons to fire messages of excitation repeatedly and intensely, thereby "strengthening" their synaptic connections with other nerve cells. The strengthening of synapses, otherwise known as long term potentiation, or LTP, is thought to be the basis of learning and establishing memories. The signal inciting this event, the researchers determined, is a cannabinoid molecule.

"Signaling by the cannabinoid system represents a mechanism by which neurons can communicate back
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Contact: Jennifer O'Brien
jobrien@pubaff.ucsf.edu
415-476-2557
University of California - San Francisco
27-Mar-2001