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Photic sensitivity ranges of hamster pupillary and circadian phase responses do not overlap.
- Source :
-
Journal of biological rhythms [J Biol Rhythms] 2008 Feb; Vol. 23 (1), pp. 37-48. - Publication Year :
- 2008
-
Abstract
- Mammalian retinal photoreceptors form an irradiance detection system that drives many nonvisual responses to light such as pupil reflex and resetting of the circadian clock. To understand the role of pupil size in circadian light responses, pupil diameter was pharmacologically manipulated and the effect on behavioral phase shifts at different irradiance levels was studied in the Syrian hamster. Dose-response curves for steady-state pupil size and for behavioral phase shifts were constructed for 3 pupil conditions (dilated, constricted, and control). Retinal irradiance was calculated from corneal irradiance, pupil size, retinal surface area, and absorption of ocular media. The sensitivity of photic responses to retinal irradiance is approximately 1.5 log units higher than to corneal irradiance. When plotted against corneal irradiance, pharmacological pupil constriction reduces the light sensitivity of the circadian system, but pupil dilation has no effect. As expected, when plotted against retinal irradiance all dose-response curves superimposed, confirming that the circadian system responds to photon flux on the retina. Pupil dilation does not increase the circadian response to increasing irradiance, since the response of the circadian system attains saturation at irradiance levels lower than those required to induce pupil constriction. The main finding shows that due to the different response sensitivities, the effect of pupil constriction on the light sensitivity of the circadian system in the hamster under natural conditions is virtually negligible. We further suggest the existence of distinct modulating mechanisms for the differential retinal irradiance sensitivity of the pupil system and the circadian system, which enables the different responses to be tuned to their specific tasks while using similar photoreceptive input.
- Subjects :
- Algorithms
Animals
Circadian Rhythm drug effects
Circadian Rhythm radiation effects
Cricetinae
Dose-Response Relationship, Radiation
Male
Mesocricetus
Motor Activity drug effects
Motor Activity radiation effects
Muscarinic Agonists pharmacology
Photoreceptor Cells drug effects
Photoreceptor Cells radiation effects
Pupil radiation effects
Quinuclidines pharmacology
Retina anatomy & histology
Retina radiation effects
Tropicamide pharmacology
Circadian Rhythm physiology
Photic Stimulation
Photoreceptor Cells physiology
Pupil physiology
Subjects
Details
- Language :
- English
- ISSN :
- 0748-7304
- Volume :
- 23
- Issue :
- 1
- Database :
- MEDLINE
- Journal :
- Journal of biological rhythms
- Publication Type :
- Academic Journal
- Accession number :
- 18258756
- Full Text :
- https://doi.org/10.1177/0748730407311851