Parkinson's disease patients could benefit from a non-invasive technique that can successfully target a highly specific group of brain cells which play a key role in development of the condition.

In a study published in the journal Neurotherapeutics a clear communication pathway between cholinergic neurons and dopaminergic neurons, two major neurotransmitter systems found in the brain, were revealed.

Dopaminergic neurons produce dopamine, but in Parkinson's disease these levels are reduced as neurons deactivate and eventually die. This can cause a number of symptoms including impaired movement.

According to Parkinson's UK, around 145,000 people in the UK are diagnosed with the disease, which has three main symptoms - shaking, slowness of movement and muscle stiffness.

Restarting the production of dopamine 

Using a type of gene therapy in a rat model of Parkinson's, Dr Ilse Pienaar, Lecturer in Pharmacology at the University of Sussex, along with colleagues at Imperial College London and Invicro, a precision medicine company, targeted cholinergic neurons, only to realise that a therapeutic knock-on effect was also felt by dopaminergic neurons. The originally stimulated cell was able to evoke a positive reaction in the receptive cell type, restoring dopaminergic functions.

With both groups of nerve cells stimulated, test subjects were seen to make a complete recovery including showing no more signs of movement and postural impairment.

Dr Ilse Pienaar, senior author of the study funded by the Medical Research Council, said: "When we used brain imaging, we found that as we activated cholinergic neurons, they then interacted directly with dopaminergic neurons. This seems to be a knock-on effect so by targeting this one set of neurons, we now know that we are able to also stimulate dopaminergic neurons, effectively restarting the production of dopamine and reducing symptoms.

"This is really important as it reveals more about how nerve systems in the brain interact, but also that we can successfully target two major systems which are affected by Parkinson's disease, in a more precise manner."

In the gene therapy technique, the team used a harmless virus to deliver a genetic modification to cholinergic neurons in rats rendered Parkinsonian. They then administered a drug designed to act as a 'switch' and stimulate target neurons.

While the disease can currently be managed by drugs, these tend to become ineffective after five years and present a number of side effects. An alternative is an invasive surgical procedure called deep brain stimulation (DBS) which uses electrodes to send pulses into the brain. However, this treatment produces mixed results and researchers believe this is because it stimulates every cell type rather than just the specific cells affected by Parkinson's disease.

Dr Pienaar said: "For the highest chance of recovery, treatments need to be focused and targeted but that requires a lot more research and understanding of exactly how Parkinson's operates and how our nerve systems work.

"Discovering that both cholinergic and dopaminergic neurons can be successfully targeted together is a big step forward. While this sort of gene therapy still needs to be tested on humans, our work can provide a solid platform for future bioengineering projects."