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A millisecond parameter space for phase-shifting the circadian pacemaker with near-ultraviolet light
Sevag Kaladchibachi1, David C Negelspach1, Jamie M Zeitzer2,3
1Department of Psychology, University of Arizona, Tucson, AZ, USA.
Summary
Brief ultraviolet-A (UVA) light flashes effectively shift circadian rhythms in fruit flies, with shorter flashes being more efficient. Aged flies show reduced sensitivity to UVA light, impacting circadian entrainment.
Area of Science:
- Chronobiology
- Insect Physiology
- Photobiology
Background:
- Circadian entrainment synchronizes internal biological clocks to external light cycles.
- The role of ultraviolet-A (UVA) light in circadian entrainment is not well understood.
- Drosophila ananassae possesses known sensitivity to short-wavelength light.
Purpose of the Study:
- To investigate the phase-shifting effects of brief UVA light flashes on circadian rhythms in Drosophila ananassae.
- To determine how UVA flash duration, frequency, and irradiance influence circadian phase shifts.
- To assess age-related changes in UVA light sensitivity for circadian entrainment.
Main Methods:
- Utilized a range of UVA LED protocols with varying flash durations, frequencies, and irradiances.
- Quantified circadian phase shifts in locomotor activity under constant darkness.
- Stimulated flies at specific circadian time points (ZT13 and ZT23) to induce delay and advance phase shifts.
- Compared responses between young and aged Drosophila ananassae.
Main Results:
- Young flies showed robust phase delays and advances in response to UVA flashes, dependent on luminance and frequency.
- Shorter UVA flash durations (especially 8 ms) demonstrated higher phase-shifting efficiency and lower energy thresholds, particularly at ZT23.
- Aged flies exhibited significantly reduced sensitivity to UVA light, especially with short (8 ms) pulses.
- Responses indicated an age-related decline in UVA-mediated circadian regulation.
Conclusions:
- The insect circadian system is sensitive to the temporal dynamics of UVA light input.
- Optimal circadian entrainment may be achieved through brief, intermittent UVA stimulation.
- Age-related decline in UVA sensitivity affects circadian regulation, potentially due to diminished photoreceptive pathways.
- Findings offer comparative insights into UVA's role in circadian timing across taxa and life stages.
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