The triad of Parkinson's is:
Bradykinesia, Rigidity and Tremor.
Other signs:
Mask-like face (apathetic), shuffling gait, depression, stooped posture, dystonia, anosmia, postural instability, generalised fatigue, micrographia, sleep disturbance and executive dysfunction.
Parkinson's can be caused genetically by alpha-synuclein gene mutation. Lewy bodies and increased ubiquitinated proteins are involved- oxidative stress can be the cause of these proteins as they create tissue damage. L-DOPA leads to the production of O2 radicals which damage the tissues.
L-Dopa is the usual treatment for dopamine deficiency as it crosses the blood brain barrier. Carbidopa and Entacapone both act in the periphery to reduce the metabolism peripherally- these drugs therefore keep the L-Dopa in a state that can cross the blood-brain barrier. Dopamine itself cannot cross the barrier.
Selegiline is a MAO-beta inhibitor which means the dopamine will stay in the synapse for longer.