Low CSF GABA in parkinsonian patients who respond poorly to therapy or suffer from the “on‐off” phenomenon

The γ‐aminobutyric acid concentration in cerebrospinal fluid was measured by radioreceptor assay in 23 parkinsonian patients (“good responders” and “poor responders” to drug therapy, “on‐off” state) and 11 age‐matched control subjects. Mean concentrations were similar but significantly lower in the poor responders and the “on‐off” state than in the good responders and control subjects. Patients who show good response to drug therapy appear to have a normal level of GABAergic activity that is not altered by drug therapy.