PhD project: Neuronal plasticity dynamics in Syrian Hamster hibernation.
Hibernation is a strategy that evolved in many animal species to see them through times of harsh conditions, e.g. the winter. During hibernation animals enter a state of torpor, in which they effectively shut down their metabolism. Deep hibernators, such as the European Ground squirrel and the Syrian Hamster, cool down to near environmental body temperatures, as a result of their decreased metabolism.
In order to maximize the energy savings it could be expected that hibernating animals maintain a low metabolic rate throughout the hibernation season. This is however not the case. Deep hibernators intersperse long (multiple days) torpid periods, with short (~12 – 24 hours) periods during which they rewarm to the euthermic level, throughout the hibernation. Moreover, they spend approximately 80% of the total amount of energy used during the entire hibernation period in these short periodic arousals to euthermy.
Because of the high energetic costs associated with periodic euthermy, many biological functions have been attributed to these periodic arousals. Based on the observation that hibernators mainly sleep during these periodic arousals, research within the Animal behaviour / Chronobiology group of The university of Groningen has mainly focussed on the need for brain maintenance processes in the euthermic intervals.
This research angle has led to the discovery of a cyclic pattern of neuronal connectivity markers in Ground squirrels over the hibernation cycle ( Strijkstra et al, 2003 ). During torpor neuronal connectivity decreases, and it is restored to normal (summer) levels during the periodic euthermic intervals. Furthermore in Ground squirrels and Hamsters the neuronal skeletal-protein-tau is hyperphosphorylated during torpor, which is a major hallmark of Alzheimer's Disease in humans. During the periodic euthermic intervals this effect is fully reversed. ( Arendt et al, 2003; Härtig et al, 2007 )
The findings so far have been based on a design aiming for differences between the torpid and the warm state of hibernating animals. As a result of that, little is known about the neuronal plasticity dynamics occurring at the transitions from the warm to the cold state and vice versa, where the brain temperature changes ~32 °C within 2-3 hours. The main goal of my PhD project will be to map the neuronal plasticity dynamics, with a focus on tau-protein-hyperphosphorylation, along the brain-temperature trajectory observed during cooling and rewarming, in hibernating Syrian Hamsters.
Furthermore I aim to investigate the functional consequences of neuronal plasticity changes during hibernation, by testing memory performance before during and after hibernation in Syrian Hamsters. Finally I am interested in comparing the neuronal and behavioural consequences of deep hibernation with those of different hibernation strategies, such as daily torpor, as can be observed in Djungarian Hamsters.
