New Depression Model Advances Disease Frontiers

A new study released today by the Centre
for Addiction and Mental Heath (CAMH) provides a thorough explanation of
how the "chemical imbalance" occurs in major depression, a disease that
impacts approximately 5 percent of people globally. For over 30 years, scientists
believed that monoamines -- mood-related chemicals such as serotonin,
norepinephrine and dopamine -- are low in the brain during major depressive
episodes. This is commonly referred to as a "chemical imbalance". However,
no one had ever found a convincing explanation for monoamine loss, until
now.



Led by CAMH's Dr. Jeffrey Meyer, this study published in the November
Archives of General Psychiatry investigated whether brain monoamine oxidase
A (MAO-A) -- an enzyme that breaks down chemicals like serotonin,
norepinephrine and dopamine -- was higher in those with untreated
depression. The results showed that in major depression MAO-A was
significantly higher in every brain region that the scientists
investigated. On average, MAO-A was 34% higher.



According to Dr. Meyer, "In major depression, higher levels of MAO-A is
the primary process that lowers monoamine levels. Having more MAO-A leads
to greater breakdown of key chemicals like serotonin."



This study includes a detailed new monoamine model of depression, based
upon this work as well as four previous publications from Dr. Meyer and
collaborators at CAMH.



Said Dr. Meyer, "A key barrier to making advances in treating
depression is a lack of precise disease models. Having disease model is
like having a map. Once you have that map you can really begin to
understand how an illness like depression works, and offer more targeted
and effective treatment."



A second part of this new model is that monoamine transporters have an
important role in removing monoamines away from active sites. Having more
of a monoamine transporter is not helpful as it removes more monoamine --
for example if one has more serotonin transporter, one would additionally
lose more serotonin during depression.



"An important aspect of our advanced monoamine model is that
individuals with depression lose chemicals like serotonin and dopamine at
different rates based upon transporter density. This helps explain why one
person with depression may experience loss of appetite while another may
not. And some people have more severe symptoms than others," said Dr.
Meyer.



This advanced monoamine model of depression is a huge step forward in
the disease frontier. It brings the study of mental illness closer to the
advancements seen in research into physical illness such as cardiac
disease, and offers one of the most comprehensive disease models in mental
illness.



The next step for researchers will be to investigate why MAO-A levels
are raised in the brain and consider prevention strategies. Prevention
strategies are critical -- according to the World Health Organization,
major depression is currently the fourth leading cause of death and
disability and is expected to rise to second by the year 2020.



To view a diagram, visit Monoamine Model of Depression
(camh/Research/Areas_of_research/new_depression_model%20.html).


More information on this field of study is available at Background
Information
(camh/Research/Areas_of_research/background_monoamine_depression.html)



The Centre for Addiction and Mental Health (CAMH) is one of the largest
addiction and mental health organizations in North America and Canada's
leading mental health and addiction teaching hospital. CAMH is a Pan
American Health Organization and World Health Organization Collaborating
Centre, and is fully affiliated with the University of Toronto. CAMH
combines clinical care, research, policy, education and health promotion to
improve the lives of people impacted by mental health and addiction issues.


Centre for Addiction and Mental Health

camh/