Aging of the trigeminal blink system

Abstract

This study characterizes trigeminal blinks in normal human subjects between 20 and 80 years of age, 60-year-old Parkinson's disease patients, and young and old guinea pigs. In normal humans over 60 years of age, lid-closing duration, and the excitability and latency of the trigeminal reflex blink increase significantly relative to younger subjects. Aged guinea pigs appear to display similar increases in reflex blink duration and latency. Reflex blink amplitude, however, does not change consistently with age. For subjects less than 70 years of age, a unilateral trigeminal stimulus evokes a 37% larger blink in the eyelid ipsilateral to the stimulus than in the contralateral eyelid, but 70-year-olds exhibit blinks of equal amplitude. In all cases, blink duration is identical for the two eyelids. If normal, age-related loss of dopamine neurons explains these trigeminal blink modifications, then Parkinson's disease should exaggerate age-related changes in these blink parameters. Preliminary data show that Parkinson's disease increases blink duration and excitability relative to age-matched control subjects. Thus, it seems likely that normal, age-related loss of dopamine neurons accounts for increases in trigeminal blink excitability and duration. A previously uncharacterized type of trigeminally evoked blink appears after age 40 in humans and in aged guinea pigs. In subjects less than 40 years old, a single trigeminal stimulus elicits a single reflex blink. In subjects over age 40, however, a single stimulus frequently evokes a reflex blink and additional blinks that occur at a fixed interval relative to the preceding blink. These "blink oscillations" may arise from oscillatory processes within trigeminal reflex blink circuits. The presence of exaggerated blink oscillations in subjects with dry eye and benign essential blepharospasm suggests that an alteration of blink oscillation mechanisms plays a critical role in these disorders.

Lid Restraint Evokes Two Types of Motor Adaptation

“…For all subjects, the mean Ϯ SEM ratios were 0.98 Ϯ 0.12 and 1.61 Ϯ 0.05. Differences in the amplitude of the two lid movements evoked by SO stimulation are typical for normal subjects (Peshori et al, 2001). Immediately after removing restraint from the left eyelid, however, left SO stimulation evoked a significantly larger blink in the left lid relative to the right lid for the subject in Figure 1 B (LSO, Post).…”

“…1 A , Post, Blink Oscillation). Because these extra blinks occurred at a relatively constant interval with respect to the onset of the preceding blink, these additional blinks were referred to as blink oscillations (Peshori et al, 2001). We estimated the most probable time for a blink oscillation to occur after the onset of the preceding blink by creating a blink density function (Fig.…”

“…Each point is the mean of at least four trials. Control subject data are from those of Peshori et al (2001). Figure 6.…”

Characterization of some morphological parameters of orbicularis oculi motor neurons in the monkey

“…However, recent efforts have focused on examining the role of the OO in neurological movement disorders affecting eyelid closure. Indeed, OO abnormalities occur in a host of neurological disorders including blepharospasm, hemifacial spasm, Meige syndrome, Parkinson's disease and Tourette's syndrome (Basso and Evinger, 1996;Hallett and Daroff, 1996;Smith et al, 1996;Schicatano et al, 1997;Jankovic and Tolosa, 1998;Peshori et al, 2001;Evinger et al, 2002;Hallett, 2002;Holstege, 2002). In many of these diseases there is a cumulative breakdown in the structural organization and functional regulation of the neural circuitry mediating OO function.…”

Animal Models for Investigating Benign Essential Blepharospasm

“…The blink system is exquisitely sensitive to central dopamine levels [71]. For spontaneous blinks, the blinks that occur without an external stimulus, systemic activation of dopamine receptors increases the blink rate and eliminating dopamine or blocking dopamine receptors reduces spontaneous blink rates [72-79].…”