Forsøksdyr: Acute and chronic effects of light and melatonin on metabolic physiology in a resident high arctic bird

Godkjenningsdato 31.10.2018

Endothermic (“warm blooded”) species undergo marked changes in metabolic physiology over daily and seasonal timescales, to optimize energy budgets to ensure survival and successful reproduction. Timing of physiological responses to environmental changes depends on brain-based daily and seasonal timer mechanisms, coupled via the endocrine and autonomic nervous systems to metabolic activity in peripheral tissues. This general area is highly relevant for assessing species capacity to respond to rapid climate change, and from human and animal health perspectives including obesity and healthy ageing.
Knowledge gap
Understanding of metabolic physiology in birds lags behind that in mammals, both for timing and effector pathways. The role of the pineal hormone melatonin in seasonal regulation in birds is not understood – while in mammals seasonal and daily melatonin cycles are closely coupled to photoperiod and are essential for control of seasonal metabolism and reproduction. It is also unclear whether food intake and metabolic control in birds depends on hypothalamic thyroid hormone metabolism, as it does in mammals.The purpose of this project is to understand the roles of light and melatonin in seasonal metabolic regulation in the Svalbard ptarmigan.
Animal model
Nobel Prize winner and physiologist August Krogh’s principle states: "for such a large number of problems there will be some animal of choice, or a few such animals, on which it can be most conveniently studied." (Am J Phys, 1929, 90:243-251). We focus on metabolic regulation in the Svalbard rock ptarmigan (SvPt, Lagopus muta hyperborea), an arctic resident bird species which is adapted to extreme photoperiod changes throughout the year. The SvPt withstands Svalbard winter conditions through controlled cycles of body fattening, plumage change and regulation of energy expenditure, with amplitudes greater than seen in any other bird species. This programmed control of metabolic function under high-latitude photoperiods makes the SvPt uniquely suited for investigating seasonal metabolic control mechanisms in birds.
We focus first on changes in photoperiod and melatonin in relation to the long-term process (Chronic study). Experiments will involve light manipulation over intensity ranges experienced by wild SvPt and administration of physiological concentrations of melatonin, while we record food intake, locomotor activity and temperature (with iButton data-loggers) in n=72 birds over 7 months. Secondly, an acute (72-h) experiment in autumn will determine how short-term light manipulations and melatonin administration affect brain pathways controlling the metabolic response, with birds (n=68) being euthanized for tissue collection. In both experiments, interventions are mild and well tolerated by the birds, but involve surgery and are, thus, moderately severe.
Replacement: There are no suitable in vitro approaches or standard laboratory animals that express similar characteristics as the SvPt.
Reduction: We use serial analysis of changes in physiological performance and behavior; individual animals act as own controls, increasing statistical power and reducing sample sizes. We retain frozen tissue samples, reducing the need for further animal experiments.
Refinement: We use laboratory-reared, tame birds, retaining the physiological and behavioural attributes of wild animals and minimising handling stress. We use analytical techniques that maximize the information gained.