The effect of one-hour hypothermia on long term spatial memory in male Long Evans rats

Abstract

The human body is willing to expend great amount of energy on mechanisms that keep the core temperature within a very small range. When these mechanisms are overwhelmed the body temperature either rises (hyperthermia) or drops (hypothermia). Hypothermia has earlier been used to induce retrograde amnesia (forgetting) and we have in this study examined if hypothermia can affect a robust long-term spatial memory like that of the water maze task.

Thirty-three male Long Evans rats were trained in the water maze task with eight sessions per day for five consecutive days. On day six a baseline Atlantis test was run before randomly allocating the animals to either deep hypothermia (24 °C), intermediate hypothermia (26, 28, 30, 32 °C) and normothermia (37.5 °C) procedure. The target temperature for the deep and intermediate hypothermia was sustained for an hour and the normothermia time controlled to the mean time spent under anesthesia for the hypothermic groups. The animals then rested for five days before a final retrieval Atlantis trial was conducted.

We found no difference between the three groups during training, at baseline or at retrieval. This meant that there was no difference in how well the groups learned the task and there was no difference in how well the groups remembered the task after five days. We did not find any FJC positive cells in the histology, but due to the lack of positive controls we cannot draw any conclusions from this.

The results from this study seem to suggest that hypothermia do not induce retrograde amnesia for the water maze task, compared to normothermia. A confounding factor might be the noise resulting from the construction work going on just outside the animal facility and the low number of animals in the study.