Although the mechanisms for selegiline's beneficial action in the treatment of Parkinson's disease are not fully understood, the selective, irreversible inhibition of monoamine oxidase type B (MAO-B) is thought to be of primary importance. MAO-B is involved in the oxidative deamination of dopamine in the brain. Selegiline binds to MAO-B within the nigrostriatal pathways in the central nervous system, thus blocking microsomal metabolism of dopamine and enhancing the dopaminergic activity in the substantial nigra. Selegiline may also increase dopaminergic activity through mechanisms other than inhibition of MAO-B. At higher doses, selegiline can also inhibit monozmine oxidase type A (MAO-A), allowing it to be used for the treatment of depression.
Dopamine is an essential chemical that occurs in many parts of the body. It is the premature degradation of dopamine that results in the symptoms of Parkinson's disease. Monoamine oxidase (MAO) is an enzyme which accelerates the breakdown of dopamine. Selegiline can prolong the effects of dopamine in the brain by preventing its breakdown through seletively blocking MAO-B. It also may prevent the removal of dopamine between nerve endings and enhance release of dopamine from nerve cells.
LD50=63 mg/kg (rats, IV)