Circadian desynchrony in the mouse: how does chronic exposure to rotating shift work-like patterns of light/dark affect circadian rhythms and neurobehavioural outcomes

Disruption of circadian rhythms is associated with several deleterious health consequences, increased prevalence of obesity, maladaptive changes in affect, and cognitive impairment. Still it is estimated that as much as 20% of the work force are exposed to this risk factor experiencing some degree of chronodisruption by way of recurring weekly patterns of shift work. It is not presently clear therefore how efficiently the mammalian circadian system entrains to alternative sleep/wake cycles such as those found in shift work schedules or what the resulting physiological and neurobehavioural changes as a result of a round-the-clock activity regime might be. The present study examines male CD-1 mice treated with three different paradigms of rapidly rotating shift work-like light/dark manipulation compared to two control groups maintained on a standard 12:12 h light/dark cycle. Animal actigraphy used to assess locomotor rhythm entrainment and circadian parameter plasticity revealed phenotypically distinct entrainment patterns for different work paradigms. In contrast to previous studies circadian desynchrony 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. To test the hypothesis that rotating light/dark cycle weakens the circadian pacemaker examination of the SCN was carried out with results indicating no aberrant upregulation of inflammatory markers and normal rhythmic expression of core molecular clock proteins PER1 and PER2. Together these observations suggest that major alterations in circadian rhythm components are induced by light/dark cycles which resemble shift work and are predictive of long term changes in behaviour and learning which persist after photoperiod has been remedied. Despite this, master pacemaker functioning appears to maintain coherency and is not weakened possibly pointing to desynchrony in peripheral clocks or a role of other mechanisms, such as stress or sleep disturbance, in mediating the effects described.

Level dc:type.qualificationlevel

masters

Grantor dc:publisher.institution

National University of Ireland Maynooth

Year dc:date.issued

2012

Author dc:creator

• McGowan, Niall

• Psychology

Language dc:language

en