Effects of Narrowband Light Rearing on Activity and the Pupil in Infant Rhesus Monkeys

Abstract

Purpose : Light affects a variety of non-image forming processes, such as circadian rhythm and the pupillary light reflex, which are mediated by intrinsically photosensitive retinal ganglion cells (ipRGCs). ipRGCs are most sensitive to short wavelength light. Thus, the spectral properties of light critically impact melanopsin-mediated ipRGC activity. The purpose of this study was to compare the effects of long- and short-wavelength ambient lighting on activity patterns and pupil responses in rhesus monkeys.

Methods : Infant rhesus monkeys were reared under short wavelength “blue” light (n=20; 465 nm; 183±28 lux) on a 12-hour light/dark cycle starting at 24.7±2.8 days of age. Animals wore a Fitbit activity tracking device from 25.4±2.4 days until 148.5±7.7 days of age. Activity was quantified as mean daily “steps” during the lights-on and lights-off periods. At 333±12 days of age, pupil responses to 1 second (s) red (651 nm) and blue (456 nm) stimuli were measured. Pupil metrics included maximum constriction and the 6s post-illumination pupil response (PIPR). Data were compared to age-matched monkeys reared under either broadband “white” light (n=18; 480 lux) or long wavelength “red” light (n=20; 630 nm; 274±64 lux).

Results : During the lights-on period, daily activity was not significantly different for monkeys reared in blue light (1215±648 steps), red light (877±574 steps), or white light (942±523 steps; P=0.07). During the lights-off period, monkeys reared in blue light exhibited significantly greater activity (91±68 steps) compared to those in white light (49±34 steps; P=0.02). There was no significant difference in lights-off activity between blue and red light (67±35 steps) reared monkeys (P=0.08) or between red and white light reared monkeys (P=0.24). Maximum pupil constriction and the 6s PIPR to 1s red and 1s blue stimuli were not significantly different between groups (P>0.05 for all).

Conclusions : Rearing monkeys in narrowband blue light resulted in increased nighttime activity, whereas narrowband red light did not significantly impact daytime or nighttime activity patterns. Therefore, exposure to 12-hour narrowband blue light resulted in greater circadian disruption compared to red light, potentially due to increased melanopsin activation in the evenings. However, normal pupil responses later in the rearing period suggests that ipRGCs adapt after long-term exposure to narrowband lighting.

This is a 2021 ARVO Annual Meeting abstract.