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Happy Hormone Dopamine Curbs Memory Loss For Alzheimer’s Sufferers

November 9, 2012
Image Credit: Photos.com

Alan McStravick for redOrbit.com – Your Universe Online

Alzheimer´s is an degenerative illness that slowly robs the sufferer of their long-term memory and, through the resultant dementia, often leaves them lost and unable to discern between present and past. There is a reason that Alzheimer´s disease is referred to as “the long goodbye”.

Led by Emrah Düzel, researchers from of the University of Magdeburg in Germany are studying the effects of the hormone dopamine and how it might work to improve long-term memory. In their tests, they monitored subjects ranging from 65 to 75 years of age who were given a precursor of dopamine before being subjected to a memory test. Their results are providing new insight into the formation of long-term memory and also giving understanding as to why memories fade more rapidly after the onset of Alzheimer´s disease. The team published their results in the Journal of Neuroscience.

Dopamine is a multi-faced neurotransmitter. Its purpose is to aid in communication between nerve cells as well as between nerve and muscle cells. Disruption of this signal transmission can lead to severe consequences. As an example, Parkinson´s disease has been recognized as a disorder that results from a lack of dopamine. With Parkinson´s, symptoms such as akinesia, or the inability to control muscle movements, are prevalent in patients.

Alternately, if someone experiences great joy or motivation, their brain is flooded with dopamine, presenting a feeling of joy or elation. This is one reason dopamine has been called the “feel-good hormone.” In previous studies, a link between dopamine and the ability to form long-lasting memories has already been established. These links stem from the observation that rewarding incidents and other important events can typically be remembered for a long time. Düzel´s current study has now been able to confirm this effect with elderly subjects.

“Our investigations for the first time prove that dopamine has an effect on episodic memory. This is the part of long-term memory, which allows us to recall actual events. Occurrences in which we were personally involved,” Düzel says.

“Episodic memory is that part of our capacity to remember, which is first affected in Alzheimer´s dementia. This is why our results can contribute to a better understanding of the disease,” explained Düzel, the Site Speaker of the German Center for Neurodegenerative Diseses (DZNE) in Magdeburg and director of the Institute of Cognitive Neurology and Dementia Research at the University of Magdeburg.

Borrowing from what we have learned through animal studies, we know that a release of dopamine from the brain is required to store experiences permanently. Düzel and his team wanted to examine if and how this process might occur in the human brain. The researchers devised a memory test wherein the 65 to 75 year old subjects were asked to recognize photos they had been shown previously. One half of the participant group had been given a placebo while the other half was given Levdopa. Levdopa, also known as L-DOPA, can be transmitted to the brain through the bloodstream. Once in the brain, it is converted into dopamine. Administering L-DOPA in this manner allowed the researchers to exercise a targeted influence over the dopamine levels in the brains of the test subjects.

“Neurons, which produce dopamine, decline with age,” Düzel says. “Increasing dopamine levels in these elderly subjects should show a clear effect.” The neuroscientist mentions another reason for undertaking the study with older people, noting: “In old age the episodic memory declines. This is why the topic we are investigating is particularly relevant for elderly people.”

The testing commenced with the elderly subjects being shown black and white photos of indoor scenes and landscapes. They were asked to differentiate these images from the others. Utilizing functional magnetic resonance tomography (fMRT) the researchers zeroed in specifically on the photos that triggered little to no activity in the memory center. The reason for this particular focus was because if the brain is only slightly active, then there should be no dopamine released. “In such cases the memory of these pictures should gradually fade. As they have encoded only weakly,” Düzel explains. “We wanted to find out whether the memory of these pictures could nevertheless persist.”

After two and then six hours following the time the participants had memorized the photos, the researchers requested of them that they recognize and distinguish them from new images.

What the researchers noted after two hours was that there was no significant difference in recall between the participants who had taken the placebo and those participants that were given L-DOPA. It was only after six hours that researchers saw a change in memory. The L-DOPA group was able to recognize a full 20 percent more of the memorized photos than the subjects in the control group.

The team was also able to determine that the ratio between the amount of L-DOPA taken and the participants´ body weight was a decisive factor in determining an optimal dose. “This confirms our assumption that dopamine contributes to anchoring memories in the brain on a permanent basis. You might say it improves the survival chances of memory content,” according to Düzel. “Our study also shows that the survival memories can be regulated, regardless of how strong these were originally encoded. This is a new finding.”

Düzel has an explanation for why it took the six hours, rather than two hours, for the effect to emerge. His theory has to do with how the brain stores memories. “When memories are encoded, certain images take place at the nerve endings, the so-called synapses,” he explains. “This activation is however only temporary, and afterwards the state of the synapses change back again. This is unless dopamine is available so that newly formed synapses can be stabilsed [sic] over a long period of time.”

According to the team, the test given at hour two must have taken place during the period of short-term synaptic activation. This might explain why both test groups had similar results at the two-hour mark. It was only later, after six hours, that the memories of the subjects who had taken the placebo began to fade. The L-DOPA group, by contrast, was able to demonstrate a significant improvement in memory retention thanks to the hormone.

Düzel and his team operated this study, giving the participants their dopamine as a precursor before being asked to memorize the photographs. They learned that the persistence of memories can be influenced. It doesn´t matter if the original memory encoding was weak or strong. The researchers believe that with their study they have opened the way for further studies. “It is conceivable that participants might receive the supplement at a later stage,” says Düzel. “The idea is that they learn something, then take the dopamine afterwards and still don´t forget what they learnt.”

Of particular, however, are the future implications that this study might have on the treatment of Alzheimer´s dementia. “The episodic memory suffers substantially when affected by Alzheimer´s. Our results show that in addition to current forms of treatment, which chiefly target certain protein deposits in the brain, other aspects should also be taken into consideration.”

“Here dopamine and the so-called neuromodulatory systems, which release chemical messengers into the brain are of particular importance. But so far, research into this topic is still in its infancy.”


Source: Alan McStravick for redOrbit.com - Your Universe Online



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