Treatment for Parkinson’s : L-DOPA
The most obvious treatment for Parkinson’s would be to replace the dopamine in the brain that is being lost by dopaminergic neuron degeneration. Dopamine itself, however, cannot pass the blood brain barrier to get into the brain. L-DOPA, the precursor of dopamine (it is broken down to create dopamine), can pass the blood brain barrier however. This means that we can administer L-DOPA, it will enter the brain, and then dopaminergic neurons with DOPA decarboxylase (the enzyme that breaks down L-DOPA) will convert L-DOPA into dopamine, giving the dopaminergic neurons that remain in the brain more dopamine to release and make up for the ones that have died.
This treatment works very well in the early stages of Parkinson’s. Unfortunately, as time goes on, more and more L-DOPA is needed to help movement because more neurons are dying in the substantia nigra and there is a bit of tolerance to L-DOPA. At the higher doses that are needed, there are much more dramatic side effects, including horrible hallucinations, twitches, obtrusive mood swings, etc. Knowing what we know about the basal ganglia circuitry, we know that these are due to increased DA activating the direct pathway of the basal ganglia and increasing thoughts/emotions as well as movements.
Unfortunately, because of these side effects, L-DOPA is just a temporary treatment and cannot be used as long-term as needed for someone trying to live with Parkinson’s disease. There are other possible treatments that I will discuss next.