Spontaneous blink rates correlate with dopamine levels in the caudate nucleus of MPTP-treated monkeys.

Previous studies have suggested a dopaminergic regulation of eye blink rates in human and nonhuman primates. Blockade of either dopamine (DA) D1 or DA D2 receptors or DA depletion induced by the dopaminergic neurotoxin MPTP both decrease spontaneous eye blink rates in monkeys. MPTP-induced decreases in blink rates can be reversed by administration of the full efficacy D1 agonist dihydrexidine, which has also been found to have dramatic antiparkinsonian effects in MPTP-treated animals. Increases in blink rates can also be induced by D1 and D2 agonists in normal animals. In the current study, we have investigated whether blink rates correlate with concentrations of DA or HVA and/or HVA:DA ratios in specific brain regions in MPTP-treated monkeys. Furthermore, the potential relationship between the severity of behavioral indices of parkinsonism and blink rates were examined. We found that (1) blink rates significantly correlate positively with concentration of DA and inversely with HVA:DA ratios in the rostral portion of the ventromedial body of the caudate nucleus (CD), but not other subcortical regions, and (2) that severity of parkinsonism was inversely correlated with blink rate. These data support a dopaminergic regulation of blink rate and suggest that the ventromedial region of the body of the CD may be critically involved in regulation of blink rate.