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   Apr 16

Heavy cannabis use ‘DOES have a negative affect on your brain – in regions linked to learning and memory’

Cannabis use lowers release of dopamine in the striatum, the area of the brain that is linked to learning and memory

Past studies shown same link for cannabis and heroin, experts say
But new research is the first time the same link has been seen with pot

Experts warn it has ‘variety of negative effects on learning and behaviour’
Smoking cannabis does have a detrimental affect on the brain, new research has shown.

The drug compromises the release of dopamine, a chemical that is integral to the brain’s reward system, in areas of the brain linked to learning and memory.

Past studies have shown that addiction to other drugs, such as cocaine and heroin, have similar effects on dopamine release, but such evidence for cannabis was missing until now.

Lead author of the new research, Professor Anissa Abi-Dargham, from Columbia University Medical Center, said: ‘The bottom line is that long-term, heavy cannabis use may impair the dopaminergic system, which could have a variety of negative effects on learning and behavior.’

Scientists at Columbia University Medical Center found those people who are heavy users of cannabis have a lower release of dopamine in the striatum – an area of the brain linked to memory and learning

Researchers noted lower levels of dopamine release in the striatum, a region of the brain that is involved in working memory, impulsive behaviour and attention.

Their study included 11 adults, between the ages of 21 and 40, who were severely dependent on cannabis and 12 matched, healthy control participants.

On average, the group of cannabis addicts started using the drug at the age of 16, and became dependent on marijuana by the age of 20.

All had been dependent for the past seven years, researchers noted.

They said in the month prior to the study, nearly all users taking part had smoked marijuana on a daily basis.

Scientists used a process called positron emission tomography (PET) to track a specific molecule that binds to dopamine receptors in the brain.

They were able to therefore measure dopamine release in the striatum and its subregions.

Furthermore they tracked dopamine release in several other regions of the brain, including the thalamus, midbrain and globus pallidus.

Those participants addicted to cannabis stayed in hospital for a week of abstinence prior to taking part in the study, to ensure that the PET scans were not measuring the acute effects of the drug.

All participants were scanned before and after being given oral amphetamine, to elicit dopamine release.

The researchers said the bottom line is ‘heavy cannabis use may impair the dopaminergic system, which could have a variety of negative effects on learning and behavior’

Compared with the participants in the control group, those who were dependent on cannabis had significantly lower dopamine release in the striatum, as well as other areas that are important for learning.

The researchers also looked at the relationship between dopamine release in a key area of the striatum and cognitive performance on learning and working memory tasks.

While there was no difference between groups in task performance, in all participants lower dopamine release was linked to worse performance on both tasks.

Dr Abi-Dargham said: ‘In light of the more widespread acceptance and use of marijuana, especially by young people, we believe it is important to look more closely at the potentially addictive effects of cannabis on key regions of the brain.’

She said it difficult to be certain whether decreased dopamine was a preexisting condition or the result of heavy cannabis use.

But added that the ‘bottom line’ is that a reliance on cannabis that leads to heavy use has a negative effect on learning and behaviour.

Jeffrey Lieberman, MD, chair of psychiatry at CUMC and past president of the American Psychiatric Association, noted that ‘these findings add to the growing body of research demonstrating the potentially adverse effects of cannabis, particularly in youth, at the same time that government policies and laws are increasing access and use’.

The research is published in the journal Molecular Psychiatry.

Source: Daily Mail

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