Summary
Researchers have discovered that antidepressant drugs such as Prozac not only affect levels of the neurotransmitter serotonin in the brain, but also "hijack" dopamine signaling as well--causing it to launch serotonin signals. Their findings offer new insight into how Prozac and other "selective serotonin uptake inhibitors" (SSRIs) work and how they might cause problems in patients taking them.
SSRIs perform their antidepressant function by increasing the concentration of serotonin in the signaling junctions, called synapses, between neurons. This increase alleviates the deficiency of serotonin that causes depression.
As their name indicates, SSRIs prevent uptake of the serotonin after it has performed its task as a chemical messenger that enables one neuron to trigger a nerve impulse in a neighbor. SSRIs prevent this uptake by inhibiting the action of the molecular cargo carriers called transporters that recycle serotonin back to the neuronal storage sacs called vesicles.
Now, however, Fu-Ming Zhou (presently at the University of Tennessee) and colleagues at Baylor College of Medicine have revealed that SSRIs can have more complex effects on neurotransmitter traffic in the brain than just altering serotonin levels. They found that higher serotonin concentrations caused by SSRIs can "trick" transporters of another key neurotransmitter, dopamine, into retrieving serotonin into dopamine vesicles. Dopamine transporters have a low affinity for serotonin, but the higher serotonin levels result in its uptake by the dopamine transporters, found the scientists.
As a result, the normal dopamine-triggered firing from such neurons, in essence, launches two different types of neuronal ammunition, causing "cosignaling."
The researchers were led to study the role of dopamine signaling in SSRI action by previous evidence that dopamine was involved in depression and in the function of antidepressants in the brain. They studied the nature and machinery of serotonin and dopamine signaling by treating mouse brain slices with fluoxetine (Prozac) and other chemicals, and analyzing the effects on the dopamine-signaling machinery.
The relatively inefficient, slow process of "hijacking" of dopamine transporters by serotonin during SSRI treatment could explain why it takes many days of treatment before antianxiety effects are seen, suggested the researchers.
Also, they wrote that their findings may explain why treatment of children with fluoxetine can induce depressive symptoms in adulthood. The researchers wrote that, since serotonin plays a vital role in neuronal development, disruption by fluoxetine of the normal serotonin levels during development could be responsible for such behavioral abnormalities.
They also theorized that such corelease of dopamine and serotonin caused by SSRIs could explain cases of a "potentially life-threatening serotonin syndrome" caused by such situations as dietary overload of serotonin precursors in people taking SSRIs.
The researchers wrote that the relationship between dopamine and serotonin signaling "is likely vital for normal behavior and for the pathology that can be treated with SSRIs." The brain area involved, the ventral striatum, "is critically involved in the neuronal processes of reward and emotional functions." Thus, they wrote, enhanced participation of the striatal dopamine system in serotonin signaling during treatment with SSRIs "may contribute to the therapeutic efficacy of SSRIs."
Original source:
http://www.eurekalert.org/pub_releases/2005-04/cp-sai040105.php
Details
SSRI antidepressants involve dopamine as well as serotonin signaling
About the author: Mike Adams is a natural health author and award-winning journalist with a strong interest in personal health, the environment and the power of nature to help us all heal He has authored more than 1,800 articles and dozens of reports, guides and interviews on natural health topics, and he has authored and published several downloadable personal preparedness courses including a downloadable course focused on safety and self defense. Adams is an honest, independent journalist and accepts no money or commissions on the third-party products he writes about or the companies he promotes. In 2010, Adams launched TV.NaturalNews.com, a natural health video site featuring videos on holistic health and green living. He's also the founder and CEO of a well known email mail merge software developer whose software, 'Email Marketing Director,' currently runs the NaturalNews email subscriptions. Adams also serves as the executive director of the Consumer Wellness Center, a non-profit consumer protection group, and pursues hobbies such as martial arts, Capoeira, nature macrophotography and organic gardening. He's also author of numerous health books published by Truth Publishing and is the creator of several consumer-oriented grassroots campaigns, including the Spam. Don't Buy It! campaign, and the free downloadable Honest Food Guide. He also created the free reference sites HerbReference.com and HealingFoodReference.com. Adams believes in free speech, free access to nutritional supplements and the ending of corporate control over medicines, genes and seeds. Known on the 'net as 'the Health Ranger,' Adams shares his ethics, mission statements and personal health statistics at www.HealthRanger.org
Have comments on this article? Post them here:
people have commented on this article.
Sunday, April 10, 2005
Email this article to a friend
Share
this article on: 
){kind=link}