The Associated Press The THC in marijuana binds to cannabinoid receptors in the brain's 'reward center.' Two UA scientists are trying to determine if these receptors can be blocked, thereby suppressing various cravings.

Studies on naturally occurring chemicals in the human brain that are very similar to marijuana may lead UA scientists toward new developments for pain treatments, neurological disorders, obesity and addiction.

Scientists are analyzing endocannabinoids, a naturally occurring substance in the brain that is closely related to cannabis, or marijuana.

Endocannabinoids are present in every human brain regardless of whether the person smokes marijuana, said Edward French, UA pharmacology professor.

More than a decade ago, scientists discovered that cannabinoid receptors are present in all vertebrate animals. These naturally occurring brain receptors bind to marijuana, triggering the effects of the drug, French said.

The discovery left scientists wondering why the brain has these receptors. The answer may have a profound effect on the future of medicine, especially when treating conditions like anxiety, French said.

Both endocannabinoids and marijuana affect the same brain system and receptors that cause feelings of pleasure, known as the "reward center," French said.

The reward center is a brain system responsible for causing pleasurable sensation from natural stimuli like sexual intercourse and eating.

The system also allows marijuana to produce similar effects because when marijuana is smoked, the drug is "hijacking" or overstimulating the system, which makes it a critical pathway for drug reward, French said.

French and his colleague, Greg Gerdeman, a postdoctoral research associate, both said they think understanding this system could lead to medicines that will treat numerous neurological conditions like anxiety and schizophrenia.

French has a license from the Drug Enforcement Agency that allows him to research tetrahydrocannabinol, or THC.

French and Gerdeman conduct experiments on lab rats with 99 percent pure synthetic delta-9 tetrahydrocannabinols. Delta-9 THC is the main psychoactive ingredient in marijuana.

By injecting THC into lab rats, French and Gerdeman look at how the chemical affects the reward center pathways in the brain.

"I'm compelled to think the endocannabinoid system is involved in the body's healing process on a lot of different levels," Gerdeman said.

Through understanding why and how the system affects the body's healing process, it can be incorporated into a view of healing and medicine that's beneficial, Gerdeman said.

"Everyone knows marijuana causes the munchies," French said.

One of the questions scientists in this field are aiming to answer is whether or not medicine can block the receptor that causes munchies after smoking marijuana, and produce an opposite effect that actually suppresses the appetite, rather than enhance it.

A drug that may be marketed as early as next year could do just that, Gerdeman said.

Rimonabant, an endocannabinoid blocker and antagonist, may become the first drug of its kind. The drug is designed to suppress appetite by enhancing or increasing the body's natural endocannabinoids by blocking its brain receptors.

As a result, Rimonabant will prolong the activity of naturally produced endocannabinoids, which may cause a person's appetite to be suppressed.

According to an article in a Newsweek special edition, "The Future of Medicine, Summer 2005," 40 percent of patients on Rimonabant lost 10 percent or more of their body weight over the course of a year.

The drug may also be marketed to suppress cravings for other drugs like nicotine, French said.

Nicotine causes the brain to release dopamine, which releases endocannabinoids. Drug manufactures think that if naturally occurring endocannabinoids aren't broken-down as quickly, the cravings for nicotine will also subside.

The way Rimonabant and other possible drugs will work is parallel to the way anti-depressant serotonin reuptake inhibitors, like Prozac, work. These anti-depression drugs block the serotonin receptors so more of the chemical remains in the brain.

Drugs like Rimonabant will use the same concept as serotonin reuptake inhibitors but with an increase of endocannabinoids instead of serotonin.

This type of research will soon change medicine "quite notably," Gerdeman said.