A new study suggests that a brain chemical that causes people to feel sleepy also plays a significant role in making deep brain stimulation a success, thereby easing the symptoms of Parkinson's disease and other brain disorders in patients.
Lead researcher Dr. Maiken Nedergaard, a neuroscientist and professor in the Department of Neurosurgery at the University of Rochester Medical Center, says that the chemical called adenosine is very important for the effectiveness of deep brain stimulation (DBS), which is used to treat people affected by Parkinson's disease and is being tested in patients with severe depression or obsessive-compulsive disorder.
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The researchers said that their study had unexpectedly given importance to the role of adenosine and to cells called astrocytes, which had been overlooked by neuroscientists for a long time.
"Certainly the electrical effect of the stimulation on neurons is central to the effect of deep brain stimulation. But we also found a very important role for adenosine, which is surprising," Nature Medicine quoted Nedergaard as saying.
Adenosine is mainly a by-product of the chemical ATP, which is the source of energy for all our cells. As the day ends, its level in the brain normally increases, and ultimately it plays a huge role in making us sleepy.
The scientists claimed that their study was the first to show the role of adenosine in deep brain stimulation.
However, though the scientists have recognized adenosine's ability to inhibit brain cell signalling, they did not suspect any role as part of DBS's effect of suppressing abnormal brain signalling.
"There are at least a dozen theories of what is happening in the brain when deep brain stimulation is applied, but the fact is that no one has really understood the process completely," said Dr. Robert Bakos, a neurosurgeon at the University of Rochester, who has performed more than 100 DBS surgeries in the last decade.
"We've all been focused on what is happening to the nerve cells in the brain, but it may be that we've been looking at the wrong cell type," he added.
During the study, the researchers found that a mixture of adenosine itself, without any deep brain stimulation, resulted in decreasing abnormal brain signalling in mice.
They have also found that a drug like caffeine, which blocks adenosine receptors, also diminishes the effectiveness of DBS. This is the reason why caffeine helps keep people awake.
"It may be possible to enhance the effectiveness of deep brain stimulation by taking advantage of the role of agents that modulate the pathways initiated by adenosine," said Nedergaard.
"Or, it's possible that one could develop another type of procedure, perhaps using local targeting of adenosine pathways in a way that does not involve a surgical procedure," she added.