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Young brain sports marijuana receptors.

The smoke from marijuana cigarette may impart only a transient high to adults, but it could have more lasting effects on infants, warn neuroscientists at the University of British Columbia in Vancouver.

Max S. Cynader and Zheng Chen report that newborn kittens and monkeys have many more receptors for cannabinoid molecules--which give marijuana its mind-altering punch--in their immature brains than do adult animals. Using a radioactive label to localize such receptors, they found that numbers peak just when the brain is most malleable. Their study focused on the cortex, the area involved in learning and cognition.

"There is a striking temporary concentration of these receptors in the visual cortex during a critical period, when the brain fine-tunes its structure and function," says Cynader. "Stimuli at that time determine how well [the brain] will work forever."

The receptors lie in the subplate, a transient scaffolding tht underlies the developing cortex. "The subplate is particularly important, because the final architecture of the cortex is being assembled from this ozone," Cynader says.

As the cortex takes shape, the subplate gradually degenerates and receptor numbers dwindle. In kittens, receptor numbers peak around 40 days after birth. The presence of the receptors in human infants has not been proved, but Cynader notes that the subplate is well developed at birth and performs functions similar to those in kittens and monkeys.

The pattern of receptors expression in animals suggests that endogenous canabinoids may play a role in setting up the cortex. But the researchers are still puzzling over just what that role may be. To unravel the mystery, they will test how drugs that stimulate or block the receptors affect cortical development, Cynader explains.
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Title Annotation:newborn kittens and monkeys have more receptors than adult counterparts for cannabinoid molecules
Author:Strobel, Gabrielle
Publication:Science News
Article Type:Brief Article
Date:Nov 27, 1993
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