Neurobiology of Parkinson's disease

Parkinson's disease is one of the most common neurodegenerative disorders. It is a chronic progressive disease characterized essentially by the progressive and irreversible destruction of dopamine-producing neurons in a specific region of the brain known as the substantia nigra leading to motor disorders such as rest tremor extrapyramidal hypertonia and bradykinesia. However other systems are also involved notably the cholinergic noradrenergic and serotonergic systems responsible for cognitive disorders non-motor symptoms as well as alterations in posture and gait. In patients with Parkinson's disease heterogeneous changes in the cholinergic noradrenergic and serotonergic systems can occur in different brain regions. These changes correlate with a variety of clinical features both motor and non-motor refractory to dopaminergic treatment and can be conceptualized within a systemic framework where nodal deficits can lead to circuit dysfunction.