A mixed D1 and D2 antagonist does not replay pattern electroretinogram alterations observed with a selective D2 antagonist in normal humans: relationship with Parkinsonʹs disease pattern electroretinogram alterations

The human retina produces a tuned response to stimuli of increasing spatial frequency reversed at a steady state. The peak amplitude response, at medium spatial frequencies, is decreased in Parkinsonʹs disease and in normal subjects (n=18) treated with a D2 dopaminergic antagonist (l-sulpiride). Here, we report that a mixed D1–D2 receptor antagonist (haloperidol) in normal subjects (n=18) does not produce an amplitude decrease of medium spatial frequencies (SFs) responses but it decreases low-frequency response. It could argued that the increased dopamine release produced by the presynaptic D2 antagonistic action of haloperidol is subsequently counteracted at postsynaptic level by its D1 antagonistic effect, producing a net counterbalance at medium SFs. These data suggest that the two dopamine receptors may play different roles in the retinal function and in the origin of visual alterations in Parkinsonʹs disease.