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Circadian rhythms in Limulus photoreceptors. II. Quantum bumps
E Kaplan1, R B Barlow, G Renninger
1Marine Biological Laboratory, Woods Hole, Massachusetts 02543.
The Journal of General Physiology
|September 1, 1990
Summary
Horseshoe crab eyes adjust their light sensitivity daily. At night, photoreceptor responses are prolonged, increasing light sensitivity, while spontaneous activity decreases.
Area of Science:
- Neuroscience
- Circadian Biology
- Vision Research
Background:
- The lateral eye of the horseshoe crab (Limulus polyphemus) exhibits daily changes in light response, controlled by a brain circadian clock.
- Efferent optic nerve fibers transmit circadian signals from the brain to the eye.
Purpose of the Study:
- To investigate the physiological and membrane property changes in single Limulus photoreceptors over several days.
- To elucidate how circadian input modulates photoreceptor function.
Main Methods:
- In vivo electrophysiological recordings from single Limulus photoreceptors over multiple days.
- Analysis of quantum bump shapes, spontaneous activity rates, resting potential, membrane resistance, and neuronal firing rates.
Main Results:
- Quantum bumps are prolonged at night, increasing the bump area by 2.4 times, enhancing light sensitivity.
- The rate of spontaneous bumps decreases by approximately threefold at night, without altering amplitude distribution.
- Resting potential, membrane resistance, and the relationship between injected current and eccentric cell firing rate remain constant throughout the day.
Conclusions:
- Efferent input from the brain modulates specific membrane properties of Limulus photoreceptors.
- This modulation, likely via ionic channels, enhances photoreceptor sensitivity to light at night.