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Brain on drugs... The science of drug receptors

POSTED 2 JUN 2005
Afghan opium crisis
Red and white flowers grow towards the blue skyAs Afghanis cope with life after the Taliban, farmers are returning to an old standby: opium, source of morphine and heroin. Embattled Afghanistan has become the world's largest grower of the crop, which is funding terrorism and warlords. On May 25, the Australian Broadcasting Corporation reported that Afghan authorities had seized four tons of opium. Afghan president Hamid Karzai has asked President Bush to combat opium by supporting rural development, not just eradication of opium poppies.

Sap from the poppy Papover somniferum (pictured below) has been used for thousands of years to relieve pain and treat symptoms of diseases. But opiates are also a major addictive drug. Photo: NIH

Opium affects the brain through chemical receptors located on nerve cells. Without these receptors, the opium poppy would be just another pretty flower. It definitely would not be carpeting Afghan hills.


Dry husks of poppies  in a fieldReceptors are structures on cell surfaces that are activated only by specific molecules, called "ligands." If the receptor works like a lock, the ligand is the key. When a ligand operates a receptor, the cell may reproduce, die or make some chemical.

Endogenous means "made in the body."

Opioids are chemicals that work like opiates (chemicals found in opium, morphine and heroin).

Cannabinoids are chemicals that act like one of the active ingredients of cannabis (marijuana).

Opium in the field. Photo: CIA


Research shows that receptors for opium and marijuana are widespread in the body, especially in the brain. The human body also produces compounds that act like opiates or marijuana to trigger these receptors.

We Why Filers couldn't help wondering: Why do we have drugs on the brain ?

Opium, heroin and marijuana are major illegal drugs, and we recognize that addiction to drugs can be harmful or deadly. We also wonder about the social cost of drug prohibition.

Hillside growing fields of poppiesOpium poppy fields in Burma, until recently the world's largest source. Photo: CIA

But we'll leave discussions of legality, morality and consequences to others. Instead, we want to examine the surprising interaction between the human body and the chemistry of such drugs. How do opiate receptors affect our response to alcohol or nicotine? How does cannabis affect the union of sperm and egg? Would we even bother to eat without opiate receptors?

Receptors for illegal drugs are everywhere!

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Megan Anderson, project assistant; Terry Devitt, editor; S.V. Medaris, designer/illustrator; David Tenenbaum, feature writer; Amy Toburen, content development executive

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