Aug 22, 2011 08:44 GMT  ·  By
The dark spot is a Lewy-body structure, in the substantia nigra of a patient suffering from Parkinson's disease
   The dark spot is a Lewy-body structure, in the substantia nigra of a patient suffering from Parkinson's disease

According to the results of a new scientific study carried out by investigators at the University of California in Los Angeles (UCLA), it would appear that suffering a traumatic brain injury (TBI) can lead to people being exposed to an increased risk of Parkinson's disease.

Similar associations between TBI and neural disorders have been made in past studies. Recently, we reported on a paper that found a link – although no causal relation – between brain trauma and patients' risk of developing schizophrenia.

In the new investigation, the UCLA team was able to determine the mechanisms underlying the link. Experts say that traumatic injuries can lead to the loss of a specific type of neurons, which apparently provide protection against the neurodegenerative form of dementia.

Experiments conducted on unsuspecting lab rats confirmed even moderate-intensity TBI can lead to a 15 percent decrease in the amount of nigrostriatal dopaminergic neurons present in the brain. Over 26 weeks, the amount of such nerve cells continued to decrease, achieving a 30 percent overall drop.

Interestingly, the research group found that the neural loss rate was accelerated considerably when the effects of TBI were cumulate to the effects of paraquat, one of the most widely-used pesticides in the world. The chemical is also a known risk factor for the development of Parkinson's.

The destruction of dopaminergic neurons is widely thought to be responsible for some of the symptoms characterizing Parkinson's, such as postural tremor and rigidity, and a set of problems with movement that are collectively termed akinesia.

“We found that with a moderate traumatic brain injury, the loss of neurons was too small in number to cause Parkinson’s disease, but it is enough to increase the risk of PD,” senior study author Dr. Marie-Francoise Chesselet explains.

“By decreasing the number of dopaminergic neurons, any further insult to the brain will be attacking a smaller number of neurons; as a result, the threshold for symptoms would be reached faster,” she adds.

“Shortly after a traumatic brain injury, these neurons are more vulnerable to a second insult,” the scientist argues. She holds an appointment as a professor of neurology and chair of the Department of Neurobiology at the university. Che Hutson, PhD, was first author of the study.

The work is detailed in the latest online issue of the esteemed medical journal Neurotrauma, PsychCentral reports. According to the team, dopaminergic neurons are important for the production of the critical neurotransmitter dopamine which, among other things, contributes to regulating movement.

“These are the first data revealing that in a model of experimental traumatic brain injury, not only do nigrostriatal dopaminergic neurons degenerate, those that survive become sensitized to paraquat toxicity,” says Dr. David A. Hovda.

The expert, also an author of the research, hold an appointment as a professor of neurosurgery and director of the UCLA Brain Injury Research Center.

“These results suggest that greater attention should be given to the long-term risk of Parkinson’s after traumatic brain injury, and that the epidemiology of both risk factors, brain injury and exposure to paraquat, should be evaluated in combination,” Chesselet concludes.