Of Pot and Rats

Those who advocate the unrestricted use of marijuana like to point out that there is no proof the drug has a lasting or harmful effect. That argument has now been undermined. At a meeting of the American Chemical Society in Washington last week, Biochemists Harris Rosenkrantz and Yugal Luthra reported the first evidence of basic--and dangerous--chemical changes in the brains of animals exposed to marijuana over a long period of time.

In a series of controlled experiments lasting three months, the scientists gave 160 rats a marijuana extract and THC. a synthetic form of the drug. The preliminary results were dramatic. Twelve of the 40 rats given the strongest doses of pot died during the tests. Even those given lighter doses showed signs of bizarre behavior. As many as half the rats tested developed tremors.

Revealing Autopsies. Within the first few days of the experiment, the scientists reported, depression occurred in many of the lab animals. Then "as tolerance [to marijuana] developed, hyperactivity became prevalent after day seven." As the tests continued, the frenzied activity of the rats began to culminate in seizures, convulsions and, in some cases, death. Autopsies revealed that the exposed rats had suffered a loss of brain protein and RNA, both of which play an important role in brain function. These changes occurred from 28 to 91 days after the first of the daily doses of marijuana.

Although the pot clearly seems responsible for both the physical and behavioral changes, the scientists were cautious in stating their conclusion: "One is tempted to speculate that neurochemical changes [in the rats' brains] are directly related to the hyperactivity and convulsions." Rosenkrantz and Luthra suggested that doctors who observe hyperactivity or convulsions in patients who are chronic pot smokers might treat them in time to prevent the possibility of even more serious illness.

The biochemists admit that their results may not be applicable to humans. They note that "feeding" the rats marijuana through tubes inserted directly into their stomachs is about one-sixth as effective as inhalation. On the other hand, the smallest chronic dosage given to any of the groups of rats was 30 times as high as that inhaled by heavy users of less potent, natural marijuana. Moreover, to duplicate the rat experiment with humans, the scientists estimated, a subject would have to puff his way through 50 joints of marijuana a day. Even so, the results of the experiment raise the possibility that the processes that took place in the brains of the test rats may also be occurring in the brains of chronic marijuana smokers.

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