Application of circadian biology to behavioural and physiological assessments in mice

Benson, Lindsay Anne (2016) Application of circadian biology to behavioural and physiological assessments in mice. DVM thesis, University of Nottingham.

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Abstract

Circadian rhythms are present in all living organisms; daily oscillations of biological process from the expression of a gene to the number of times that an animal displays a given behaviour. The light/dark cycle is the primary cue that entrains these rhythms and the suprachiasmatic nuclei, within the hypothalamus are the central pacemaker which synchronises peripheral body clocks. Mice are useful circadian biology models and two peripheral circadian outputs were studied, locomotor activity and the rhythm of body temperature in a common inbred strain, the C57BL/6 mouse.

The use of individually ventilated cages to house mice increases biocontainment, enabling the maintenance of high health status colonies and reducing the risk of allergies for laboratory personnel. The effect of these sealed units on ambient light levels was examined, using locomotor activity as a marker of entrainment to the light/dark cycle. Mice housed closer to the overhead light source experienced greater levels of illumination than those at the lower levels, yet all entrained to the light/dark cycle. Mice housed lower on the rack showed more activity during light hours when they normally rest and the onset of activity was advanced in relation to the time the lights turned off. Individually ventilated cages do not therefore compromise circadian entrainment but cage position may alter the distribution of rest and activity in relation to the light cycle.

Measuring the rhythm of body temperature of animals is often confounded by the stress associated with immobilisation and restraint. A novel non-invasive method, a thermal imaging camera was trialled against an indwelling intraperitoneal implant, to compare the relationship between peripheral and core body temperature under different light cycles. A stable relationship was found between the two methods (average R² value = 0.92) and this persisted in conditions of constant darkness, where lack of light cues resulted in free-running of the rhythm, assuming a shorter period length of oscillation. This novel method has potential for use in circadian phenotyping studies and to improve welfare, following experimental interventions where the mouse, a small, metabolically active animal is at risk of hypothermia.

Item Type: Thesis (University of Nottingham only) (DVM)
Supervisors: Haig, David
Subjects: Q Science > QP Physiology > QP1 Physiology (General) including influence of the environment
Faculties/Schools: UK Campuses > Faculty of Medicine and Health Sciences > School of Veterinary Medicine and Science
Item ID: 38836
Depositing User: Benson, Lindsay
Date Deposited: 14 Mar 2017 12:12
Last Modified: 19 Oct 2017 17:34
URI: http://eprints.nottingham.ac.uk/id/eprint/38836

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