The push-pull action of dopamine on spatial tuning of the monkey retina:: the effects of dopaminergic deficiency and selective D1 and D2 receptor ligands on the pattern electroretinogram.

Retinal dopamine depletion in monkeys using either systemic MPTP or 6-OHDA results in attenuated electroretinographic (ERG) responses to peak spatial frequency stimuli. Diverse dopamine receptors have been identified in the primate retina. ERG studies performed using Haloperidol (a mixed antagonist), L-Sulpiride (D-2 antagonist) and CY 208-243 (a D-1 agonist) cause spatial frequency dependent diverse effects. 'Tuning' of the normal spatial contrast response PERG, was quantified by dividing the amplitude of the response at the peak spatial frequency with the amplitude to the low spatial frequency response yielding a number greater than one. Tuning for the pharmacological experiments was defined by dividing the actual amplitude obtained at the normal peak response with the actual amplitude at the low spatial frequency response. The PERG spatial contrast response function is discussed as the envelope output of retinal ganglion cells or the average or 'equivalent' retinal ganglion cell. However, we postulate the existence of two dopamine sensitive pathways with different weights for two classes of ganglion cells. It is inferred that D-1 receptors are primarily affecting the 'surround' organization of ganglion cells with large centers, while D-2 post-synaptic receptors contribute to 'center' response amplification of ganglion cells with smaller centers. These inferences are consistent with some lower vertebrate data. It is also inferred that low affinity D-2 autoreceptors may be involved in the D-1 'surround' pathway. An understanding of the logic performed by retinal D-1 and D-2 receptors may be useful to discern the functional role of diverse dopamine receptors in DA circuits elsewhere in the CNS. (C) 1998 Published by Elsevier Science Ltd. All rights reserved.