The effect of apomorphine on blink kinematics in subhuman primates with and without facial nerve palsy.

PURPOSE

The purpose of this study was to document the effect of acutely delivered apomorphine, a dopamine receptor agonist with both D1 and D2 properties, on blink rate and the amplitude-velocity characteristics of eyelid kinematics in a group of nonhuman primates.

METHODS

Three cynomolgus and two rhesus macaques underwent baseline recordings for eyelid kinematics, using the Robinson search coil technique. Next, each animal received a 0.15-mg/kg subcutaneous injection of apomorphine. Recordings were taken at 45 and 90 minutes, respectively, after injection. Blink rates per minute were obtained, and main sequence relationships were calculated for every animal. The data were pooled for each eyelid, excluding one monkey who was affected by facial nerve palsy and was analyzed separately.

RESULTS

Monkeys with normal facial musculature and normal baseline blink rates showed consistently longer, faster blinks after apomorphine. The main sequence relationship, although tending to be lower, was not statistically different from baseline. One monkey, with prior facial nerve palsy and a very steep amplitude versus peak velocity relationship, showed normalization of the main sequence slope after apomorphine at both 45 and 90 minutes after injection.

CONCLUSIONS

Apomorphine consistently lowers blink rate and changed blink metrics in normal monkeys and, more dramatically, in a monkey with facial nerve palsy. These findings add credence to models in which dopamine deficiency plays a role in the modulation of blink kinematics.