Selective effects of low doses of apomorphine on spatiotemporal contrast sensitivity in healthy volunteers: a double‐blind placebo‐ controlled study.

Abstract

1. Apomorphine (1 and 5 micrograms kg‐1) and placebo were given to nine normal volunteers, using a Latin‐square design and double‐blind procedures. The visual perception of static and moving patterns (static and motion contrast sensitivity) was evaluated before and 15 min after the dose administration. 2. Apomorphine (1 and 5 micrograms kg‐1), as compared with placebo, led to a significant overall reduction of the visual perception of movement. This effect was dose‐related, and apomorphine (5 micrograms kg‐1) induced a more pronounced decrease in the visual perception of movement than apomorphine (1 microgram kg‐1). With apomorphine (5 micrograms kg‐1), the reduction was more pronounced for low spatial frequencies, and was linearly inversely correlated to the spatial frequency for a temporal frequency of 3 Hz. Finally, no significant effect of apomorphine was observed for sensitivity to static patterns. 3. Several non exclusive hypotheses may be suggested: The effects of apomorphine may result from stimulation of retinal D1‐ and/or D2‐dopaminergic receptors. Apomorphine may increase the surround inhibition of ganglion cells' receptive‐fields. This modification of the centre‐surround balance may explain the decrease in contrast sensitivity for low spatial frequencies. The specific effects of apomorphine on the visual perception of movement support the hypothesis that apomorphine preferentially affects the magnocellular pathway which mediates sensitivity to moving patterns.

GABA‐ergic control of visual perception in healthy volunteers: effects of midazolam, a benzodiazepine, on spatio‐temporal contrast sensitivity.

“…Thus, the results cannot be simply related to sedation and were probably a specific set of effects. In fact, we observed fundamental differences between the effects of MDZ and those related to normal ageing [26] or apomorphine administration [28].…”

“…Moreover, colour vision in vertebrates mediated by the parvocellular pathway, is also assumed to be related to GABA A receptors [49]. By contrast, we previously demonstrated that apomorphine preferentially reduced sensitivity to moving patterns at low spatial frequencies [28]. This result might be interpreted as a preferential involvement of the dopaminergic system in magnocellular pathways, which have broad band characteristics, with high sensitivity to contrast and temporal modulation, and mediate motion perception and stereopsis [48].…”

“…It is a better predictor of the visual system's performance than is pure visual acuity, and it gives a more complete description of the functional range of the visual system [25]. STCS modifications have been demonstrated across the life span [26], in pathological conditions such as Parkinson's disease [26,27] and under the influence of pharmacological treatments [28].…”

Parkinson's disease, visual hallucinations and apomorphine: A review of the available evidence

“…color perception, visual acuity, visual object, and space perception) remain unchanged. A decrease in contrast sensitivity was found after infusion of apomorphine in healthy volunteers [82,83], suggesting that overstimulation of retinal or cortical dopamine receptors may result in reduced lower-order visual perception. The absence of a positive effect on higher-order perceptual functions in PD patients with VH might be related to a dosing-or a ceiling effect.…”

“…Enhanced dopamine levels are found in early PD patients resulting in impaired prefrontal functioning [78][79][80] presumably due to frontal compensation [81]. With disease progression, the number of prefrontal D1-like receptors is reduced and prefrontal functioning deteriorates [80,[82][83][84].…”