Behavior/Humans

Marijuana Shapes Our Brains Even from the Womb

Endocannabinoids tell the neurons how to connect

By Stefan Anitei, Science Editor

26th of May 2007, 13:21 GMT

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After all, marijuana is not so bad.

Cannabis-made marijuana may be easing the pain, but marijuana-like chemicals produced by your body may have head brain cells to make proper connections while you are the size of a bean inside the womb.

These chemicals, called cannabinoids, were found to work like guideposts for neurons of fetal mouse brains. This could explain why the children of marijuana smoking mothers are slower in neural processes than others (but not less intelligent).

Tetrahydrocannabinol (THC), the main active chemical in marijuana, could impair the cell-guiding pattern by overstimulating the brain, but the precise effects of endocannabinoids (natural brain chemicals) and THC on developing human brains are still not known.

"Scientists know that particular receptor proteins on human and animal adult brain cells respond to THC-like chemicals, or cannabinoids, which prevent the cells from making strong connections to one another," said co-author Tibor Harkany, neurobiologist of the Karolinska Institute in Stockholm.

Harkany's team exposed mouse embryonic brain cells expressing cannabinoid receptor proteins (CBRs) to gradients of synthetic cannabinoids. The neurons withdrew their rootlike expansions (axons) from the high cannabinoid concentration areas. The axons, which realize the inter-neuronal connections, changed their directions.

"If you activate the cannabinoid system of these cells, it will send a message to the cell that 'I don't want to grow there, I want to grow somewhere else", said Harkany.

Two groups of mice embryonic neurons were found to carry the CBR proteins for several days during late womb development (which lasts in 18 or 19 days). These neurons were found in the cortex, the brain part involved in thinking, learning, attention and planning in humans and mammals.

"THC would likely affect very similar brain systems in human fetuses, but its concentration would be much higher than that of any endocannabinoid. It would have an even more pronounced effect on axonal growth and guidance," said neuroscientist Yasmin Hurd of the Mount Sinai School of Medicine in New York City.

"Natural cannabinoids can reach very high concentrations but are secreted by the brain in precise locations. THC would activate CBRs indiscriminately. The effects of endocannabinoids released in a regulated fashion will almost always be different from THC from smoked cannabis." said co-author Ken Mackie, neuroscientist of Indiana University.

TAGS:

cannabis | brain | receptor

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