People who regularly use marijuana show significant abnormalities in areas of the brain associated with motivation and emotion, a team of Swiss researchers has found. The scientists discovered changes in the volume of grey matter — the tissue containing brain cells — in regular marijuana users compared with occasional ones.
Marijuana, the most commonly used illicit drug in the United States, is associated with various cognitive impairments. Animal studies have uncovered structural changes in brain regions rich in cannabinoid CB1 receptors, but little is known about how the drug affects the structure of the human brain.
In their study of 47 marijuana users, which was published in
Neuropsychopharmacology, the researchers used Magnetic Resonance Imaging (MRI) technology to compare the brains of regular and occasional users. Regular users smoked a joint at least 10 times a month, while occasional users smoked at least one joint per month but not more than one joint per week.
“Brain structure changes were investigated in a group of regular cannabis smokers and compared with a group of occasional smokers enrolled in our previous functional study,” the researchers wrote. “The subjects in the two groups did not use any drug other than cannabis and were free from psychiatric disorders. We then stratified the two groups according to the age of first cannabis use in order to assess the effect of cannabis on the developing brain.”
In some brain regions, the regular users showed decreased gray matter compared to occasional users, while in other regions the regular users showed increased gray matter.
The researchers found lower gray matter volume in regular marijuana users in the medial temporal cortex, temporal pole, parahippocampal gyrus, left insula, and orbitofrontal cortex. These brain regions are associated with decision making, emotion, and motivation.
Changes to the insula “have also been confirmed in alcohol addiction where the decrease in insular activation seems to reflect an inability to switch from interoceptive cravings to cognitive control for suppressing internal needs,” the researchers explained.
The researchers found higher gray matter volume in regular marijuana users in the cerebellum — the brain’s motor control center. The finding suggests that marijuana use could impair the normal “pruning back” of nerve cells in the cerebellum during adolescence and early adulthood.
“One possible reason for abnormal pruning could be the toxic effect of THC at a critical period of brain maturation,” the researchers explained. “Exogenous cannabinoids might disturb this system by competing for the receptors, thus inhibiting the pruning particularly in receptor-rich areas like the cerebellum or the prefrontal cortex.”
A similar brain imaging study, published in The Journal of Neuroscience, found the nucleus accumbens of marijuana users was abnormally large compared to non-users.
Some studies have found the brain abnormalities associated with marijuana use return to normal after periods of abstinence. The Swiss scientists called for longitudinal studies to better understand these brain changes.
“The design of our study cannot address whether the structural alterations observed are permanent or reversible,” they wrote.
Decreased dopamine brain reactivity in marijuana abusers is associated with negative emotionality and addiction severity
Contributed by Joanna S. Fowler, June 20, 2014 (sent for review April 9, 2014; reviewed by Bertha Madras, Harvard University Medical School, and Karen Berman, National Institute of Mental Health)
Marijuana abusers show lower positive and higher negative emotionality scores than controls, which is consistent, on one hand, with lower reward sensitivity and motivation and, on the other hand, with increased stress reactivity and irritability. To investigate this aspect of marijuana’s impact on the human brain, we compared the brain’s reactivity in marijuana abusers vs. controls when challenged with methylphenidate (MP). We found that marijuana abusers display attenuated dopamine (DA) responses to MP, including reduced decreases in striatal distribution volumes. These deficits cannot be unambiguously ascribed to reduced DA release (because decreases in nondisplaceable binding potential were not blunted) but could reflect a downstream postsynaptic effect that in the ventral striatum (brain reward region) might contribute to marijuana’s negative emotionality and addictive behaviors.
Moves to legalize marijuana highlight the urgency to investigate effects of chronic marijuana in the human brain. Here, we challenged 48 participants (24 controls and 24 marijuana abusers) with methylphenidate (MP), a drug that elevates extracellular dopamine (DA) as a surrogate for probing the reactivity of the brain to DA stimulation. We compared the subjective, cardiovascular, and brain DA responses (measured with PET and [11C]raclopride) to MP between controls and marijuana abusers. Although baseline (placebo) measures of striatal DA D2 receptor availability did not differ between groups, the marijuana abusers showed markedly blunted responses when challenged with MP. Specifically, compared with controls, marijuana abusers had significantly attenuated behavioral (“self-reports” for high, drug effects, anxiety, and restlessness), cardiovascular (pulse rate and diastolic blood pressure), and brain DA [reduced decreases in distribution volumes (DVs) of [11C]raclopride, although normal reductions in striatal nondisplaceable binding potential (BPND)] responses to MP. In ventral striatum (key brain reward region), MP-induced reductions in DVs and BPND (reflecting DA increases) were inversely correlated with scores of negative emotionality, which were significantly higher for marijuana abusers than controls. In marijuana abusers, DA responses in ventral striatum were also inversely correlated with addiction severity and craving. The attenuated responses to MP, including reduced decreases in striatal DVs, are consistent with decreased brain reactivity to the DA stimulation in marijuana abusers that might contribute to their negative emotionality (increased stress reactivity and irritability) and addictive behaviors.
• Author contributions: N.D.V., G.-J.W., and J.S.F. designed research; G.-J.W., F.T., D.A., and M.J. performed research; D.A. contributed new reagents/analytic tools; M.J. recruited and screened volunteers; N.D.V., G.-J.W., J.L., C.W., and D.T. analyzed data; and N.D.V. and J.S.F. wrote the paper.
• No author conflict of interest response is available.
This is a vital paper, as it clearly outlines that ongoing opiate use ages the users faster than the non-drug using population; even more so in women who are seven times more susceptible to this process . The evidence also impugns the benign nature of long term Opiate Substitute Treatments.
Data show that lifetime opioid exposure, an interactive cardiovascular risk factor, particularly in women, is related to linear, quadratic, cubic and quartic functions of treatment duration and is consistent with other literature of accelerated ageing in patients with Opiate Dependency.
D.E.A. Strategies to stall/reverse supply chain abuses of Prescribed Opiates. ‘Medicine’ is being hijacked and misused only adding to the vulnerability of the already questionable efficacy of Opioid Substitute Treatments.
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The rates of amphetamine abuse and manufacture are amongst the highest in the world a trend which is particularly documented in Australia.
The domestic manufacture in Australia is widespread.
After cannabis, amphetamine arrests were second highest of all illicit drug arrests in Australia.
Australian criminal groups have developed innovating ways to adapt the manufacture of amphetamines.
Australians in their twenties had the highest prevalence rate of amphetamine abuse.
(Source: International Narcotics Control Board report released 5 March 2013)
Amphetamine (speed) manufacture in Australia is controlled by criminal groups who are responding to the demand.
Laboratories are being detected all over Australia.
Their use causes addiction like other illicit drugs and unpredictable violence, aggression and paranoia makes users dangerous to health workers who attempt to assist them.
Brain and immune system damage, heart problems, stroke, high blood pressure and even death are the risks users take.
Of particular concern is that users are most likely to be young.
Amphetamine users are particularly likely to be in need of drug rehabilitation to get them free of their use and save others from their violence.
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