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Circadian and behavioural responses to shift work-like schedules of light/dark in the mouse.

McGowan NM, Coogan AN - J Mol Psychiatry (2013)

Bottom Line: It is not presently clear therefore how efficiently the mammalian circadian system entrains to alternative light/dark cycles such as those found in shift work schedules.In contrast to previous studies the shift work-like conditions did not produce changes in animal body-weight.These results indicate that exposure to alternating patterns of light and dark as experienced by millions of shift workers may produce long-lasting changes in both mammalian circadian and neurobehavioural systems.

View Article: PubMed Central - PubMed

Affiliation: Department of Psychology, National University of Ireland Maynooth, County Kildare, Ireland.

ABSTRACT

Background: Disruption of circadian rhythms is associated with several deleterious health consequences and cognitive impairment. It is estimated that as many as one in five workers are exposed to this risk factor due to experiencing some degree of chronodisruption by way of recurring patterns of shift work. It is not presently clear therefore how efficiently the mammalian circadian system entrains to alternative light/dark cycles such as those found in shift work schedules.

Methods: The present study examines male CD-1 mice exposed to three different paradigms of rapidly rotating shift work-like light/dark manipulations compared to control animals maintained on a standard 12:12 h light/dark cycle.

Results: Analysis of circadian patterns of behaviour under such conditions reveals that for fast rotating schedules of light/dark there is minimal circadian entrainment. Further, when placed in constant conditions after a period under the "shift work" lighting conditions there were changes to circadian period associated with the shift work schedules. In contrast to previous studies the shift work-like conditions did not produce changes in animal body-weight. Behavioural testing suggests possible anxiogenic and hyperactive outcomes dependent on rotation speed as animals displayed open field thigmotaxis and hyperlocomotion.

Conclusion: These results indicate that exposure to alternating patterns of light and dark as experienced by millions of shift workers may produce long-lasting changes in both mammalian circadian and neurobehavioural systems.

No MeSH data available.


Related in: MedlinePlus

Circadian period and rhythm power across the three shift work-like schedules. Mean (A) period and (B) rhythm power during the phases of the behavioural intervention in the control, Fwd, Bck and Alt groups. LD1 refers to the initial period in a 12:12 LD cycle, SW for the last 3 weeks in under the appropriate shift work protocol, DD for constant darkness following the shift work protocol and LD2 for the 12:12 LD cycle at the conclusion of circadian rhythm monitoring. ** represents P < 0.01, * P < 0.05 compared to the initial LD values for that shift work group (Bonferroni post hoc test, # P < 0.05 compared to corresponding value for the control group (Tukey HSD test). N = 8 for each group.
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Fig3: Circadian period and rhythm power across the three shift work-like schedules. Mean (A) period and (B) rhythm power during the phases of the behavioural intervention in the control, Fwd, Bck and Alt groups. LD1 refers to the initial period in a 12:12 LD cycle, SW for the last 3 weeks in under the appropriate shift work protocol, DD for constant darkness following the shift work protocol and LD2 for the 12:12 LD cycle at the conclusion of circadian rhythm monitoring. ** represents P < 0.01, * P < 0.05 compared to the initial LD values for that shift work group (Bonferroni post hoc test, # P < 0.05 compared to corresponding value for the control group (Tukey HSD test). N = 8 for each group.

Mentions: Observation of actograms of animals from the Fwd and Bck intervention groups suggests that animals arrange locomotor rhythms in a similar fashion. Following normal as expected entrainment to the baseline LD cycle, upon exposure to the fast rotating schedules there appears to be initial attempts of the animals to track their onsets of activity to the onset of darkness (Figures 1 and 2). However, for the final three cycles of the shift work schedules there appears to be a minimal entrainment of the onsets of activity to the time of lights off, with the rhythms appearing to resemble that of a free running animal with a period of greater than 24 hours. The Alt group of animals appears to attempt to track the onset of darkness, with activity onsets showing a greater propensity to lock into the light/dark cycle than the Fwd or Bck groups (Figures 1 and 2). Analysis of rhythm period and power across the 3 shift work groups for the protocol stages of (1) the initial stable LD period (LD1), (2) the final three weeks of the shift work protocol (SW), (3) the period of DD following termination of the shift work schedule and (4) the period of stable 12:12 LD (LD2) at the end of circadian monitoring reveals a number of significant findings. For period, there is a main effect of protocol stage (F (3, 63) = 16.8, P < 0.001) and a main effect of shift work group (F (2,21) = 15.6, P < 0.001), but no group x stage interaction. Post-hoc analysis reveals that both the Fwd and the Bck groups showed lengthening of the period in the shift work phase compared to the LD or DD phases (Figure 3A). For rhythm power, there is a main effect of protocol stage (F (3,63) = 8.1) and a stage x shift work group interaction (F (6, 63) = 3.7, P < 0.01). Post-hoc analysis revealed that the Alt group showed a significant increase in the rhythm power in the shift work phase compared to in LD (Figure 3B). When comparing free-running periods in DD for the three shift work groups compared to that of controls there was a significant lengthening of period in the animals that had previously exposed to the Fwd protocol and a shortening of period in animals exposed to the Alt protocol compared to controls (Figure 3A). The animals previously exposed to the Alt protocol also showed an increase in their rhythm power in DD compared to controls (Figure 3B).Figure 1


Circadian and behavioural responses to shift work-like schedules of light/dark in the mouse.

McGowan NM, Coogan AN - J Mol Psychiatry (2013)

Circadian period and rhythm power across the three shift work-like schedules. Mean (A) period and (B) rhythm power during the phases of the behavioural intervention in the control, Fwd, Bck and Alt groups. LD1 refers to the initial period in a 12:12 LD cycle, SW for the last 3 weeks in under the appropriate shift work protocol, DD for constant darkness following the shift work protocol and LD2 for the 12:12 LD cycle at the conclusion of circadian rhythm monitoring. ** represents P < 0.01, * P < 0.05 compared to the initial LD values for that shift work group (Bonferroni post hoc test, # P < 0.05 compared to corresponding value for the control group (Tukey HSD test). N = 8 for each group.
© Copyright Policy - open-access
Related In: Results  -  Collection

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Fig3: Circadian period and rhythm power across the three shift work-like schedules. Mean (A) period and (B) rhythm power during the phases of the behavioural intervention in the control, Fwd, Bck and Alt groups. LD1 refers to the initial period in a 12:12 LD cycle, SW for the last 3 weeks in under the appropriate shift work protocol, DD for constant darkness following the shift work protocol and LD2 for the 12:12 LD cycle at the conclusion of circadian rhythm monitoring. ** represents P < 0.01, * P < 0.05 compared to the initial LD values for that shift work group (Bonferroni post hoc test, # P < 0.05 compared to corresponding value for the control group (Tukey HSD test). N = 8 for each group.
Mentions: Observation of actograms of animals from the Fwd and Bck intervention groups suggests that animals arrange locomotor rhythms in a similar fashion. Following normal as expected entrainment to the baseline LD cycle, upon exposure to the fast rotating schedules there appears to be initial attempts of the animals to track their onsets of activity to the onset of darkness (Figures 1 and 2). However, for the final three cycles of the shift work schedules there appears to be a minimal entrainment of the onsets of activity to the time of lights off, with the rhythms appearing to resemble that of a free running animal with a period of greater than 24 hours. The Alt group of animals appears to attempt to track the onset of darkness, with activity onsets showing a greater propensity to lock into the light/dark cycle than the Fwd or Bck groups (Figures 1 and 2). Analysis of rhythm period and power across the 3 shift work groups for the protocol stages of (1) the initial stable LD period (LD1), (2) the final three weeks of the shift work protocol (SW), (3) the period of DD following termination of the shift work schedule and (4) the period of stable 12:12 LD (LD2) at the end of circadian monitoring reveals a number of significant findings. For period, there is a main effect of protocol stage (F (3, 63) = 16.8, P < 0.001) and a main effect of shift work group (F (2,21) = 15.6, P < 0.001), but no group x stage interaction. Post-hoc analysis reveals that both the Fwd and the Bck groups showed lengthening of the period in the shift work phase compared to the LD or DD phases (Figure 3A). For rhythm power, there is a main effect of protocol stage (F (3,63) = 8.1) and a stage x shift work group interaction (F (6, 63) = 3.7, P < 0.01). Post-hoc analysis revealed that the Alt group showed a significant increase in the rhythm power in the shift work phase compared to in LD (Figure 3B). When comparing free-running periods in DD for the three shift work groups compared to that of controls there was a significant lengthening of period in the animals that had previously exposed to the Fwd protocol and a shortening of period in animals exposed to the Alt protocol compared to controls (Figure 3A). The animals previously exposed to the Alt protocol also showed an increase in their rhythm power in DD compared to controls (Figure 3B).Figure 1

Bottom Line: It is not presently clear therefore how efficiently the mammalian circadian system entrains to alternative light/dark cycles such as those found in shift work schedules.In contrast to previous studies the shift work-like conditions did not produce changes in animal body-weight.These results indicate that exposure to alternating patterns of light and dark as experienced by millions of shift workers may produce long-lasting changes in both mammalian circadian and neurobehavioural systems.

View Article: PubMed Central - PubMed

Affiliation: Department of Psychology, National University of Ireland Maynooth, County Kildare, Ireland.

ABSTRACT

Background: Disruption of circadian rhythms is associated with several deleterious health consequences and cognitive impairment. It is estimated that as many as one in five workers are exposed to this risk factor due to experiencing some degree of chronodisruption by way of recurring patterns of shift work. It is not presently clear therefore how efficiently the mammalian circadian system entrains to alternative light/dark cycles such as those found in shift work schedules.

Methods: The present study examines male CD-1 mice exposed to three different paradigms of rapidly rotating shift work-like light/dark manipulations compared to control animals maintained on a standard 12:12 h light/dark cycle.

Results: Analysis of circadian patterns of behaviour under such conditions reveals that for fast rotating schedules of light/dark there is minimal circadian entrainment. Further, when placed in constant conditions after a period under the "shift work" lighting conditions there were changes to circadian period associated with the shift work schedules. In contrast to previous studies the shift work-like conditions did not produce changes in animal body-weight. Behavioural testing suggests possible anxiogenic and hyperactive outcomes dependent on rotation speed as animals displayed open field thigmotaxis and hyperlocomotion.

Conclusion: These results indicate that exposure to alternating patterns of light and dark as experienced by millions of shift workers may produce long-lasting changes in both mammalian circadian and neurobehavioural systems.

No MeSH data available.


Related in: MedlinePlus