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 rate s in human and nonhuman primates. Blockade of either dopamine (DA) D1 or DA D2 receptors or DA depletion induced by the dopaminergic neurotoxin MPTP b oth decrease spontaneous eye blink rates in monkeys. MPTP-induced decreases in blink rates can be reversed by administration of the full efficacy D1 a gonist dihydrexidine, which has also been found to have dramatic antiparkin sonian effects in MPTP-treated animals. Increases in blink rates can also b e 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 monke ys. Furthermore, the potential relationship between the severity of behavio ral indices of parkinsonism and blink rates were examined. We found that (1 ) blink rates significantly correlate positively with concentration of DA a nd 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. T hese 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. (C) 1999 Academic Press.