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Colour as a signal for entraining the mammalian circadian clock.

Walmsley L, Hanna L, Mouland J, Martial F, West A, Smedley AR, Bechtold DA, Webb AR, Lucas RJ, Brown TM - PLoS Biol. (2015)

Bottom Line: Thus, our data show that some clock neurons are highly sensitive to changes in spectral composition occurring over twilight and that this input dictates their response to changes in irradiance.Finally, using mice housed under photoperiods with simulated dawn/dusk transitions, we confirm that spectral changes occurring during twilight are required for appropriate circadian alignment under natural conditions.Together, these data reveal a new sensory mechanism for telling time of day that would be available to any mammalian species capable of chromatic vision.

View Article: PubMed Central - PubMed

Affiliation: Faculty of Life Sciences, University of Manchester, Manchester, United Kingdom.

ABSTRACT
Twilight is characterised by changes in both quantity ("irradiance") and quality ("colour") of light. Animals use the variation in irradiance to adjust their internal circadian clocks, aligning their behaviour and physiology with the solar cycle. However, it is currently unknown whether changes in colour also contribute to this entrainment process. Using environmental measurements, we show here that mammalian blue-yellow colour discrimination provides a more reliable method of tracking twilight progression than simply measuring irradiance. We next use electrophysiological recordings to demonstrate that neurons in the mouse suprachiasmatic circadian clock display the cone-dependent spectral opponency required to make use of this information. Thus, our data show that some clock neurons are highly sensitive to changes in spectral composition occurring over twilight and that this input dictates their response to changes in irradiance. Finally, using mice housed under photoperiods with simulated dawn/dusk transitions, we confirm that spectral changes occurring during twilight are required for appropriate circadian alignment under natural conditions. Together, these data reveal a new sensory mechanism for telling time of day that would be available to any mammalian species capable of chromatic vision.

No MeSH data available.


Related in: MedlinePlus

Colour changes associated with natural twilight influence circadian entrainment.(A) Top: Example body temperature traces from two Opn1mwR mice. Mice were exposed to sequential 14 d epochs of (i) simulated “natural” twilight (replicating natural changes in irradiance and colour during a northern-latitude summer), (ii) 18:6 square wave LD cycle, and (iii) a twilight photoperiod which lacked changes in colour (irradiance profile identical to “natural” but relative cone opsin excitation fixed to mimic night spectra). Dotted red lines indicate timing of peak body temperature from last 9 d in each photoperiod. Bottom plot indicates timing of peak body temperature for each individual (n = 10); bars represent median. Temperature cycles were significantly phase-advanced under the irradiance-only versus natural twilight (paired t test; p = 0.003). (B) Mice lacking functional cone phototransduction (Cnga3-/-) exhibit identical phase of entrainment under both photoperiods (conventions as in A; paired t test; p = 0.51, n = 9) with peak body temperature occurring significantly earlier versus wild-type mice under natural but not irradiance-only twilight (unpaired t tests, p = 0.005 and 0.91 respectively). The data used to make this figure can be found in S5 Data.
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pbio.1002127.g005: Colour changes associated with natural twilight influence circadian entrainment.(A) Top: Example body temperature traces from two Opn1mwR mice. Mice were exposed to sequential 14 d epochs of (i) simulated “natural” twilight (replicating natural changes in irradiance and colour during a northern-latitude summer), (ii) 18:6 square wave LD cycle, and (iii) a twilight photoperiod which lacked changes in colour (irradiance profile identical to “natural” but relative cone opsin excitation fixed to mimic night spectra). Dotted red lines indicate timing of peak body temperature from last 9 d in each photoperiod. Bottom plot indicates timing of peak body temperature for each individual (n = 10); bars represent median. Temperature cycles were significantly phase-advanced under the irradiance-only versus natural twilight (paired t test; p = 0.003). (B) Mice lacking functional cone phototransduction (Cnga3-/-) exhibit identical phase of entrainment under both photoperiods (conventions as in A; paired t test; p = 0.51, n = 9) with peak body temperature occurring significantly earlier versus wild-type mice under natural but not irradiance-only twilight (unpaired t tests, p = 0.005 and 0.91 respectively). The data used to make this figure can be found in S5 Data.

Mentions: We found that the inclusion of colour significantly altered the phase of circadian entrainment. Peak body temperature occurred consistently later when irradiance and colour elements of twilight were included compared to the irradiance signal alone (Fig 5A; 31 ± 8 min; paired t test, p = 0.003; n = 10). This distinction was absent in mice lacking cone phototransduction (Cnga3-/-, [29,30]; Fig 5B; 6 ± 9 min; paired t test, p = 0.51; n = 9), confirming that it originated with cone-dependent colour coding, rather than any differences in the pattern of rod/melanopsin activation between the two photoperiods.


Colour as a signal for entraining the mammalian circadian clock.

Walmsley L, Hanna L, Mouland J, Martial F, West A, Smedley AR, Bechtold DA, Webb AR, Lucas RJ, Brown TM - PLoS Biol. (2015)

Colour changes associated with natural twilight influence circadian entrainment.(A) Top: Example body temperature traces from two Opn1mwR mice. Mice were exposed to sequential 14 d epochs of (i) simulated “natural” twilight (replicating natural changes in irradiance and colour during a northern-latitude summer), (ii) 18:6 square wave LD cycle, and (iii) a twilight photoperiod which lacked changes in colour (irradiance profile identical to “natural” but relative cone opsin excitation fixed to mimic night spectra). Dotted red lines indicate timing of peak body temperature from last 9 d in each photoperiod. Bottom plot indicates timing of peak body temperature for each individual (n = 10); bars represent median. Temperature cycles were significantly phase-advanced under the irradiance-only versus natural twilight (paired t test; p = 0.003). (B) Mice lacking functional cone phototransduction (Cnga3-/-) exhibit identical phase of entrainment under both photoperiods (conventions as in A; paired t test; p = 0.51, n = 9) with peak body temperature occurring significantly earlier versus wild-type mice under natural but not irradiance-only twilight (unpaired t tests, p = 0.005 and 0.91 respectively). The data used to make this figure can be found in S5 Data.
© Copyright Policy
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4401556&req=5

pbio.1002127.g005: Colour changes associated with natural twilight influence circadian entrainment.(A) Top: Example body temperature traces from two Opn1mwR mice. Mice were exposed to sequential 14 d epochs of (i) simulated “natural” twilight (replicating natural changes in irradiance and colour during a northern-latitude summer), (ii) 18:6 square wave LD cycle, and (iii) a twilight photoperiod which lacked changes in colour (irradiance profile identical to “natural” but relative cone opsin excitation fixed to mimic night spectra). Dotted red lines indicate timing of peak body temperature from last 9 d in each photoperiod. Bottom plot indicates timing of peak body temperature for each individual (n = 10); bars represent median. Temperature cycles were significantly phase-advanced under the irradiance-only versus natural twilight (paired t test; p = 0.003). (B) Mice lacking functional cone phototransduction (Cnga3-/-) exhibit identical phase of entrainment under both photoperiods (conventions as in A; paired t test; p = 0.51, n = 9) with peak body temperature occurring significantly earlier versus wild-type mice under natural but not irradiance-only twilight (unpaired t tests, p = 0.005 and 0.91 respectively). The data used to make this figure can be found in S5 Data.
Mentions: We found that the inclusion of colour significantly altered the phase of circadian entrainment. Peak body temperature occurred consistently later when irradiance and colour elements of twilight were included compared to the irradiance signal alone (Fig 5A; 31 ± 8 min; paired t test, p = 0.003; n = 10). This distinction was absent in mice lacking cone phototransduction (Cnga3-/-, [29,30]; Fig 5B; 6 ± 9 min; paired t test, p = 0.51; n = 9), confirming that it originated with cone-dependent colour coding, rather than any differences in the pattern of rod/melanopsin activation between the two photoperiods.

Bottom Line: Thus, our data show that some clock neurons are highly sensitive to changes in spectral composition occurring over twilight and that this input dictates their response to changes in irradiance.Finally, using mice housed under photoperiods with simulated dawn/dusk transitions, we confirm that spectral changes occurring during twilight are required for appropriate circadian alignment under natural conditions.Together, these data reveal a new sensory mechanism for telling time of day that would be available to any mammalian species capable of chromatic vision.

View Article: PubMed Central - PubMed

Affiliation: Faculty of Life Sciences, University of Manchester, Manchester, United Kingdom.

ABSTRACT
Twilight is characterised by changes in both quantity ("irradiance") and quality ("colour") of light. Animals use the variation in irradiance to adjust their internal circadian clocks, aligning their behaviour and physiology with the solar cycle. However, it is currently unknown whether changes in colour also contribute to this entrainment process. Using environmental measurements, we show here that mammalian blue-yellow colour discrimination provides a more reliable method of tracking twilight progression than simply measuring irradiance. We next use electrophysiological recordings to demonstrate that neurons in the mouse suprachiasmatic circadian clock display the cone-dependent spectral opponency required to make use of this information. Thus, our data show that some clock neurons are highly sensitive to changes in spectral composition occurring over twilight and that this input dictates their response to changes in irradiance. Finally, using mice housed under photoperiods with simulated dawn/dusk transitions, we confirm that spectral changes occurring during twilight are required for appropriate circadian alignment under natural conditions. Together, these data reveal a new sensory mechanism for telling time of day that would be available to any mammalian species capable of chromatic vision.

No MeSH data available.


Related in: MedlinePlus