In a study, researchers measured the levels of dopamine in the substantia nigra of postmortem brains from patients diagnosed with Parkinson's disease and compared them to age-matched controls. Patients showed approximately 70-80% loss of dopamine-producing neurons. Researchers also gave living patients L-dopa, a precursor to dopamine, and observed reductions in tremor and rigidity in many patients within hours of administration.
Which conclusion is best supported by the L-dopa results?
- Acheck_circle
Dopamine deficiency in motor pathways causes the motor symptoms of Parkinson's disease.
- B
Parkinson's disease is caused by excess dopamine in the cerebellum.
- C
L-dopa replaces serotonin in motor neurons.
- D
The substantia nigra is responsible for memory consolidation.
Explanation
The improvement after taking L-dopa, which the brain converts into dopamine, supports the conclusion that low dopamine in the basal ganglia/substantia nigra pathway causes Parkinsonian motor symptoms. Excess dopamine is associated with schizophrenia, not Parkinson's.