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Testing the heat constraint hypothesis of limits on maximal energy intake in mice

Reference	BB/C504794/1
Principal Investigator / Supervisor	Professor John Speakman
Co-Investigators / Co-Supervisors	Dr Elzbieta Krol
Institution	University of Aberdeen
Department	School of Medical Sciences
Funding type	Research
Value (£)	287,250
Status	Completed
Type	Research Grant
Start date	01/06/2005
End date	31/05/2008
Duration	36 months

Abstract

Energy is a unifying currency useful for understanding evolutionary trade-offs because everything that animals do require it. The maximal rate of energy intake is a key trait because it sets a maximum limit on activities that animals can perform. This is important in the context of modelling the impacts of global climate change on animal distributions. That climate change has such effects is clear. Anticipating the effects of changes in climate, however, is less certain, because the mechanisms that link climatic conditions to animal performance, and hence distributions, are obscure ¿ particularly for endothermic animals. The question this research addresses is, what imposes this maximal limit? By understanding what imposes such limits we will have a greater understanding of the factors that govern animal performance. Historically work in this area has concerned the period of late lactation because at that stage female small mammals eat between 3 and 6 times their habitual intake when not breeding. Yet there is good evidence that in any given condition intake reaches a limit. Several hypotheses have been previously advanced to explain the limits on intake that appear to apply in this phase of the life cycle. One hypothesis is that the limits are imposed by the capacity of the mammary gland to synthesise milk, another is that the limits are imposed by the capacity of the alimentary tract to absorb energy. In 2001 my laboratory published a series of 5 papers demonstrating that both of these hypotheses are wrong. In the last 6 months we have published a series of 3 papers in which we proposed a new hypothesis and provided some preliminary supportive evidence for it. This novel hypothesis is that the limits are imposed by the capacity of the lactating female to dissipate heat. If correct this hypothesis will have some important ramifications for our understanding of sustained limits in animal performance. This grant proposal involves a series of experiments that aim to test the heat dissipation limits hypothesis, and elucidate the mechanism by which heat dissipation influences milk production and food intake. The first two experiments will involve manipulating heat flows without changing the ambient temperature. This will be performed by first, shaving mice to enhance their capacity to lose heat, and second by using mice that have transgenic upregulation of uncoupling protein-3 (UCP-3), levels, elevating their endogenous heat generation. The heat dissipation hypothesis predicts an increase in lactation performance of the shaved mice, and a decrease in the transgenic mice. The mechanism underpinning the link of temperature to lactation may be a direct consequence of hyperthermia inhibiting milk production. Alternatively when mothers suckle they may develop hyperthermia, causing them to interrupt suckling bouts, thereby inhibiting milk production. We will investigate the importance of these factors by observing the body temperatures of female mice during and between suckling bouts at different ambient temperatures (Experiment 3). In addition we will observe transgenic UCP-3 overexpressing mice nursing transgenic or wild type litters, and wildtype animals nursing transgenic or wild type litters (Experiment 4). Finally we will raise some animals where the nest and feeding sites are at different temperatures to examine the roles of within and outside the nest hyperthermia in lactation.

Summary

unavailable

Committee	Closed Committee - Animal Sciences (AS)
Research Topics	X – not assigned to a current Research Topic
Research Priority	X – Research Priority information not available
Research Initiative	X - not in an Initiative
Funding Scheme	X – not Funded via a specific Funding Scheme

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