Parkinson's disease is described as a neurodegenerative disorder caused by the death of dopamine-generating cells in the substantia nigra. It is due to this cellular death and decreased dopamine that motor symptoms arise.
A relative increase of acetylcholine occurs. This is because as dopamine decreases, there is an imbalance of neurotransmitters required for motor control. There is not a gross excess of acetylcholine, but rather an imbalance, leading to a higher acetylcholine in comparison to dopamine.
Commonly used Parkinson's drugs can be remembered by the acronym BALSA: Bromocriptine, Amantadine, Levodopa, Selegiline, Antimuscarinics.
Bromocriptine is an ergot alkaloid. It is a potent dopamine agonist, and increases its availability in Parkinson's disease. It also effects serotonergic, alpha adrenergic and glutamate receptors.
Amantadine is an interesting medication because it has activity as an antiparkinsonian medication, as well as an antiviral medication. It increases dopamine release by a poorly understood mechanism and also has anticholinergic action.
Levodopa, also known as L-Dopa, is a dopamine isomer which is commonly administered with carbidopa. L-Dopa is protected from breakdown by carbidopa in the gut and periphery and readily passes through the blood-brain barrier to increase central dopamine bioavailability.
MAO-B is an enzyme which metabolizes dopamine in the body. Selegiline is an MAO-B inhibitor, and prevents breakdown of dopamine, increasing its bioavailability.
Antimuscarinic drugs, such as benztropine, block muscarinic receptors to curb cholinergic neuron activity. This class of drugs works to alleviate tremor and rigidity associated with Parkinson's, but does not work well at treating bradykinesia.
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