Parkinson's Disease Affects the Cerebral Basal Ganglia, Resulting in Tremors

Parkinson's disease affects the cerebral basal ganglia, resulting in tremors in limbs, slowness in beginning and completing movements, and other abnormalities of muscle control.The specific population of neurons involved degenerates and thus fails to produce the neurotransmitter dopamine.An obvious treatment option to try is to administer dopamine, yet this is completely ineffective at alleviating the symptoms.Propose a reason why this treatment fails, and a related alternative to address the dopamine deficit.(Hint: Think about how the brain protects itself from chemicals in the blood.)