What Is Dopamine? Dopamine is a simple organic chemical used as a neurotransmitter that performs a variety of important functions within and without the brain, including motor control, learning, immune response, kidney and pancreatic function. The chemical is transmitted along specialized Dopaminergic neurons throughout the brain and, while there are not more than 400,000 total such neurons (a minuscule portion of the 100 billion or so in the human brain), their effects are wide ranging and intense.
How It Works In Your Brain - "Our understanding of dopamine has gone through several reiterations," says Michael Treadway, PhD, a clinical fellow at McLean Hospital and Harvard Medical School. Dopamine "works" by binding to a neuron's surface receptors (specifically G protein-coupled receptors), causing either the excitation or inhibition of the target cell via an opening of sodium or potassium channels, respectively. Science hasn't yet tacked down the complete functional capabilities of the body's numerous dopamine systems but do understand a large part of its role in reward-motivated behavior and response selection. Basically, the more dopamine released in response to a certain action — say, sex, cocaine, or even the unassuming "runner's high" — the more likely you are to perform that action again.
How It Interacts with THC - According to a newly published study from teams at Imperial College London, University College London (UCL), and King's College London, long-term habitual use of marijuana can lead to severe dopaminergic dysfunction. Specifically, the study found that the bodies of weekly, heavy tokers — those with borderline cannabis dependence — produce far less dopamine than those of non-users or social smokers. What's more, the dopamine heavy users did produce rarely made it into the brain's striatum region, leading to decreased motivation levels.
What It All Means - It means that you should regulate your cannabis intake the same way you do with alcohol, salt, red meat, porn, hyper-porn, and all the other fun things in life that can potentially kill you — that is, responsibly. It means that you can't smoke an eighth of weed a day for 25 years without potentially (severely) impacting your mental health — and that's not even to mention what it does to your lungs. Not to mention that it's still illegal in Australia, so you shouldn't do it anyway.
Even
as the body of evidence of cannabis' potential as a potent medical precursor
grows (especially with the development of CBD-rich strains), smoking it is not
without long-term side effects. And we're not just talking about
munchie-induced weight gain either. A number of recently published studies
suggest habitually getting high not only kills your motivation, it might even
alter your brain chemistry. Specifically, the part that makes you want to get
off the couch.
For
all of its benefits, the mounting evidence suggests that THC's effects on your
dopamine levels might not just make you lazy. It could cause some more serious
medical issues as well. So what exactly is going on here?
These
cells are concentrated primarily in the substantia nigra, a part of the basal ganglia located in the midbrain, and the ventral
tegmental area (VTA),
also in the midbrain. These neurons spread out from the substantia nigra into
the striatum, globus
pallidus, and subthalamic nucleus, which all play important
roles in motor control — the highest forms being motivation and decision-making
while lower forms include sexual arousal, nausea, and lactose production — and
response selection. From the VTA these neurons fan out into the nucleus accumbens and prefrontal cortex, both of which regulate motivation
response and reward.
A
number of diseases are thought to be the result of altered dopamine levels.
Restless Leg Syndrome, and ADHD have all been linked to low dopamine levels,
while elevated levels are routine for schizophrenics. Researchers believe that
the substantia nigra, in particular, plays a role in the onset of Parkinson's syndrome — when these few cells die off,
the amounts of dopamine vs acetylcholine are thrown out of balance and the
disease is more likely to take hold.
Dopamine
effectively regulates your "effort threshold," the likelihood that
you'll perform an action after weighing the required costs and potential
benefits. If you have more dopamine in your system, you're more likely to
undertake an action than if you had less dopamine coursing through your head.
Not
only that, dopamine acts as a potent teaching device, training the basal
ganglia to evoke whatever action elicited the dopamine release rather than
another action that does not. Again the more dopamine your body releases, the
more likely you are to do whatever released it. As such, elevated dopamine
levels have been linked to increased motor activity and impulsive behavior (as evidenced here)
while low levels of the neurotransmitter leaves people lethargic, depressed,
and unmotivated.
For
example, Dr Treadway and his team from Vanderbilt University studied the
effects of naturally occurring dopamine levels on the decisions made by 25
volunteers, ages 19 to 29. The volunteers were given a series of tasks with a
variety of associated dollar amounts. Easy tasks, such as pushing a button 7
times in 30 seconds with your dominant index finger paid out less than tougher
tasks like pressing said button 100 times in 21 seconds with your off-hand
pinkie. And while the subjects were button-mashing, Treadway's team was
monitoring their brain activity using positron emission tomography (PET) scans.
The
results, published in the Journal
of Neuroscience, found that people who undertook and completed
a higher proportion of hard vs easy tasks over the course of the 20-minute test
also had higher levels of dopamine in the striatum and ventromedial prefrontal
cortex (regions associated with reward and motivation), while those subjects
that performed proportionally fewer hard tasks had higher levels of dopamine in
a brain region called the insula.
"The
folks with relatively more striatal dopamine were focused on the reward,"
Treadway told WebMD. "The folks with more insular dopamine were thinking
about how tired their pinky was. They were focused on the costs."
Essentially your level of motivation depends on where the dopamine in your head
is flowing. And in chronic smokers, it barely flows at all.
The
teams performed PET scans on the striatum of 19 regular cannabis users and 19
non-users, matched for age and sex. The smokers had all started using cannabis
between the ages of 12 and 18, all admitted to having psychotic-like symptoms
while under the influence at one point or another (i.e.: paranoia, altered
mindset, etc).
The
team had expected to see elevated dopamine levels among the stoners but found
the opposite: the earlier they started smoking and more frequently/heavily they
smoked, the lower their baseline dopamine levels compared to the control group.
"Long-term
regular marijuana use seems to have a [strong] effect on brain chemistry,"
says Michael Bloomfield, Ph.D., lead author of the study said in a press
release. "After a period of time, your brain cells aren't able to make as
much tyrosine hydroxylase, an important enzyme that's a key component in making
dopamine. We know that dopamine affects how the brain controls motivation
and addictions; therefore our study provides a
scientific explanation as to the reason that cannabis users seem to become less
motivated."
Bloomfield
continued: It has been assumed that cannabis
increases the risk of schizophrenia by inducing the same effects on the
dopamine system that we see in schizophrenia, but this hasn't been studied in
active cannabis users until now. The results weren't what we expected, but they
tie in with previous research on addiction, which has found that substance
abusers — people who are dependent on cocaine or amphetamine, for example —
have altered dopamine systems.
This
study did only focus on users that reported psychotic effects while high, but
is confident that the findings can be extrapolated out to the wider
understanding of addiction and mental illness in general.
Unfortunately
we can only talk about the effects of THC on the brain in broad strokes;
cannabis research has been stunted from 43 years of prohibition under Schedule One of the Controlled
Substances Act.
Whatever we still don't know, it's not for lack of motivation to find out.
Norb
Leahy, Dunwoody GA Tea Party Leader
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