Exploratory Study of the Expression of the Serotonergic 5-HT4 Receptor in Parkinson's Disease (PARK 5-HT4)

Inclusion Criteria: Man or woman : Age between ≥ 50 and ≤ 85 years old For women: postmenopausal Affiliated to a social security scheme or similar; Having given written consent to participate in the free and informed study. Level of study: ≥ 6 years of schooling only for healthy volunteer : No history of neurological or psychiatric disease Only for patient : Having a clinically established or probable diagnosis of Parkinson's disease according to the criteria defined by the Movement Disorder Society at a Hoehn and Yahr stage ≤ 3 (in on dopa conditions) and a duration of evolution of the disease between 2 and 8 years. Only for patient : Having a MoCA (Montreal Cognitive Assessment) ≥ 20/30. Exclusion Criteria: Diagnosis other than Parkinson's disease ( for patient only) Treated with specific serotonin inhibitors (SSRIs), specific noradrenaline inhibitors (SNRIs), tricyclic antidepressants, monoamine oxidase inhibitors (MAOIs) and neuroleptics in the last 3 months Use of recreational drugs interfering with the serotonergic system (ecstasy, MDMA) or opioids (cannabis, opiates) in the last 3 months or chronic use Contraindication to magnetic resonance imaging (MRI) or positron emission tomography (PET) Participation in the last year to a study using ionizing radiation or concomitant participation in another research project involving the human being that may interfere with the results or the conclusions of this study Exceeding the annual amount of compensation authorized for participation in research protocols Deprivation of liberty by judicial or administrative decision, person subject to a legal protection measure BMI ≥ 35kg/m2 Presence of depression (BDI-2 score ≥21), anxiety (Parkinson Anxiety Scale (PAS) score ≥14) or apathy (STARKSTEIN score ≥14) - (for healthy volunteers only) Cognitive impairment (MOCA score ≤26) (for healthy volunteers only) Current or past neurological or psychiatric pathology (for healthy volunteers only) Serious and progressive medical pathology Current or past dependence on any addictive substance according to DSM-V (The Diagnostic and Statistical Manual of Mental Disorders) criteria (alcohol, cannabis, hallucinogens, inhalants, opiates, sedatives, stimulants), except tobacco and caffeine. (for healthy volunteers only)