A single bout of torpor in mice protects memory processes

Abstract

NOWAKOWSKI, S. G., S. J. SWOAP, AND N. J. SANDSTROM. A single bout of torpor in mice protects memory processes. PHYSIOL BEHAV 00(0) 000-000, 2008. -Memory consolidation is the process by which new and labile information is stabilized as long-term memory. Consolidation of spatial memories is thought to involve the transfer of information from the hippocampus to cortical regions. While the hypometabolic and hypothermic state of torpor dramatically changes hippocampal connectivity, little work has considered the functional consequences of these changes. The present study examines the role of a single bout of shallow torpor in the process of memory consolidation in mice. Adult female C57Bl/6NHSD mice were trained on the Morris Water Maze (MWM) task. Immediately following acquisition, the mice were exposed to one of four experimental manipulations for 24 hours: fasted at an ambient temperature of 19°C, fasted at 29°C, allowed free access to food at 19°C, or allowed free access to food at 29°C. Mice fasted at 19°C entered a bout of torpor as assessed by core body temperature while none of the mice in the other conditions did so. Spatial biases were then assessed with a probe trial in the MWM. During the probe trial, mice that had entered torpor and mice that were fed at 29°C spent twice as much time in the prior target platform location than mice that were fed at 19°C and those that were fasted at 29°C. These findings demonstrate that, while food restriction or cool ambient temperature independently disrupt memory processes, together they cause physiological changes including the induction of a state of torpor that results in functional preservation of the memory process.

Tau phosphorylation‐associated spine regression does not impair hippocampal‐dependent memory in hibernating golden hamsters

“…The preservation of spatial memory in Golden hamsters is in agreement with the studies in mice where single bouts of starvation-induced torpor do not impair spatial memory in a Morris water maze (Nowakowski et al, 2009). However, in European ground squirrels, an impairment of spatial memory was observed following hibernation (Millesi et al, 2001).…”

Obese mice on a high‐fat alternate‐day fasting regimen lose weight and improve glucose tolerance

“…Mice were intentionally housed at an ambient temperature that is common among most animal facilities and also is conducive to torpor in the calorically deprived mouse (23 °C). Warmer temperatures inhibit entry into torpor in mice (Koizumi et al., ; Nowakowski et al., ). Despite the relatively cool ambient temperature and multiple weeks of caloric restriction, none of the mice entered torpor throughout the entirety of the current study.…”

Human torpor: translating insights from nature into manned deep space expedition

“…Post‐training cooling results in an impairment in memory consolidation, whereas already cached information appears to be unaffected (Fulton et al ., 2008). Intriguingly, a single bout of shallow torpor can protect mice against either food restriction or low T a ‐induced spatial memory impairment (Nowakowski, Swoap & Sandstrom, 2009). The sequelae of prolonged torpor on cognition are likely to be more complex and severe than after hypothermia in non‐hibernating species, since substantial impairment in neural network function would arise from irreversible retraction of synaptic contacts and regression of spines during torpor.…”

“…Injecting leptin to signal large energy stores can reverse deep torpor and modest hypothermia (Gavrilova et al ., 1999), while injecting ghrelin to mimic a status of starvation can deepen the bout of torpor in mice (Gluck et al ., 2006). A non‐pharmacological method that employed food restriction coupled with cool T a successfully induced torpor in mice (Nowakowski et al ., 2009; Sunagawa & Takahashi, 2016). Food restriction alone also can result in hypometabolism and hypothermia in mice (Williams et al ., 2002; Brown & Staples, 2010; Lo Martire et al ., 2018).…”