No evidence of the usefulness of eye blinking as a marker for central dopaminergic activity

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Abstract
This study aimed to evaluate eye blinking as a marker for central dopaminergic activity by investigating the effects of sulpiride (D2-antagonist) and lisuride (D2-agonist) on spontaneous eye blinks. Twelve healthy subjects were included in a randomized, double-blind, placebo-controlled, three-period crossover trial. They received sulpiride 400 mg, lisuride 0.2 mg and placebo on different occasions. Eye blinks, prolactin, finger tapping, eye movements and visual analogue scales were measured at baseline and regularly for 12 h after administration. No effect of sulpiride or lisuride was observed on the number of eye blinks. Sulpiride caused an increase in prolactin (643 U/ml) [confidence interval (CI) 549–737). Lisuride caused a decrease in smooth pursuit eye movements (–4.1%) (CI –7.3 to –0.9) and visual analogue scales for mood (–2.1 mm) (CI –3.7 to –0.4). Spontaneous eye blink rate was not affected by sulpiride and lisuride, which makes eye blinking not suitable as a marker for central D2 activity.