- The neurotransmitter dopamine plays a vital role in causing behavior related to the avoidance of specific threats.
- Lower amount of dopamine in the brain may result in avoidance - behavior related to pain and fear.
- Endocannabinoids used to stimulate dopamine production may help treat diseases like depression and PTSD, both associated with low levels of dopamine.
For the first time, a new study has found a
direct causal link between the neurotransmitter dopamine and avoidance
behaviour, which includes behavior in response to pain or fear. The study
conducted by a research team from the University of Maryland School of Medicine
is published in the journal Current Biology.
Dopamine is a neurotransmitter released by
neurons in the brain. It is also called the 'feel good
' hormone, which
has been long known to play a major role in driving behavior related to
pleasurable goals, such as food, sex and social interaction. The new study for
the first time establishes time that dopamine is central in causing behavior
related to the avoidance of specific threats.
‘Lower levels of neurotransmitter dopamine in the brain may cause avoidance behavior.’
"This study really advances what we know
about how dopamine
affects aversively motivated behaviors,"
said Joseph F. Cheer PhD, a professor in the UMSOM Department of Anatomy &
Neurobiology and the study's corresponding author. "In the past, we
thought of dopamine as a neurotransmitter involved in actions associated with
the pursuit of rewards. With this new information we can delve into how dopamine
affects so many more kinds of motivated behavior."
The role of dopamine in avoidance behavior
was studied in rats focusing on a particular brain area, the nucleus accumbens.
This region of the brain plays a crucial role in linking the need or desire for
a given reward - food, sex, and so on - with the motor response to actually
obtain that reward.
, a relatively new technique, was used to modulate neuronal stimulation
even when the rats were in their natural environment. In this technique
specific groups of neurons can be controlled by exposure to light. In this
study, the team used a blue laser to stimulate genetically modified rats whose
dopamine neurons could be controlled to send out more or less dopamine.
The animals were subjected to small electric
shocks and were also taught how to escape the shocks by pressing a small lever.
Meanwhile, the team also controlled the amount of dopamine released by neurons
in the nucleus accumbens using optogenetics.
Animals with high levels of dopamine in the
nucleus accumbens learned to avoid the electric shock more quickly and did so
more often than animals that had a lower level of dopamine in this region.
Endocannabinoids are brain chemicals that
resemble the active ingredients in marijuana and play key roles in many brain
processes. When the study examined the role of endocannabinoids in dopamine
regulation, the team found that these chemicals essentially open the gate that
allows the dopamine neurons to fire. Moreover, when the level of
endocannabinoids was reduced, the animals were much less likely to move to
Dr. Cheer's team suggest that the study
findings shed light on disorders like post-traumatic stress disorder (PTSD)
and depression, both of which may involve abnormally low levels of dopamine,
and may be seen on some level as a failure of the avoidance system.
While dopamine is already being prescribed to some
patients to treat such diseases, the use of endocannabinoid drugs to treat
these conditions is under clinical trials.References:
- Jennifer M. Wenzel, Erik B. Oleson, Willard N. Gove, Anthony B. Cole, Utsav Gyawali, Hannah M. Dantrassy, Rebecca J. Bluett, Dilyan I. Dryanovski, Garret D. Stuber, Karl Deisseroth, Brian N. Mathur, Sachin Patel, Carl R. Lupica, Joseph F. Cheer. Phasic "Dopamine Signals in the Nucleus Accumbens that Cause Active Avoidance Require Endocannabinoid Mobilization in the Midbrain". Current Biology, (2018); DOI: 10.1016/j.cub.2018.03.037