Dopamine autoreceptor function is lost in advanced Parkinson's disease.

Objective: Regional presynaptic dopaminergic function and its regulation by dopamine agonists in different stages of PD can be measured by L-[11C]dopa and PET. In the current investigation, we studied the effects of therapeutic apomorphine on L-[11C]dopa uptake in patients with early and advanced PD.

Background: With disease progression and chronic dopamine agonist treatment, motor response complications supervene in a majority of PD patients.

Pyridoxine effect on synthesis rate of serotonin in the monkey brain measured with positron emission tomography.

The influence of the co-factor pyridoxine, vitamin B6, on the activity of aromatic amino acid decarboxylase enzyme was studied by positron emission tomography, PET in the brain of the Rhesus monkey using the precursor for serotonin synthesis 5-hydroxy-L-tryptophan (5-HTP) radiolabelled with 11C in the beta-position. The rate constant for the formation of serotonin in the corpus striatum was calculated using a two tissue compartment model with reference area in the brain. In baseline investigations, the mean rate constants (+/-S.