The symptoms of Parkinson's Disease (PD) are caused by the impairment or loss of neurons in the substantia nigra and/or the arcuate nucleus of the hypothalamus. These neurons produce the ‘feel good’ neurotransmitter dopamine. However, this signalling molecule within the brain also plays a central role in our ability to move.
Swedish pharmacologist and neuroscientist Arvid Carlsson discovered in 1957 that dopamine was concentrated in the basal ganglia, the portion of the brain that controls movement. Carlsson found that a deficiency of dopamine in the brain can result in the uncoordinated movements of PD while an excess of the neurotransmitter can cause tics. Basal ganglia depend on dopamine and its dopamine receptors, D1 through 5.
The main therapy for PD is levodopa, also called L-dopa, a precursor to dopamine. Nerve cells use levodopa to make dopamine. L-dopa crosses the protective blood-brain barrier, whereas dopamine cannot. People with PD also lose the nerves that produce norepinephrine. This molecule is central to the control of heart rate, blood pressure and more.
Scientists do not know what causes the dopamine producing cells to die although science points to combination of genetics and environment including exposure to certain toxins. A strong link has been found between PD and exposure to pesticides and herbicides.