von der Ohe Christina G, Darian-Smith Corinna, Garner Craig C, Heller H Craig
Department of Biological Sciences, Stanford University, Stanford, California 94305-5020, USA.
J Neurosci. 2006 Oct 11;26(41):10590-8. doi: 10.1523/JNEUROSCI.2874-06.2006.
Hibernating mammals are remarkable for surviving near-freezing brain temperatures and near cessation of neural activity for a week or more at a time. This extreme physiological state is associated with dendritic and synaptic changes in hippocampal neurons. Here, we investigate whether these changes are a ubiquitous phenomenon throughout the brain that is driven by temperature. We iontophoretically injected Lucifer yellow into several types of neurons in fixed slices from hibernating ground squirrels. We analyzed neuronal microstructure from animals at several stages of torpor at two different ambient temperatures, and during the summer. We show that neuronal cell bodies, dendrites, and spines from several cell types in hibernating ground squirrels retract on entry into torpor, change little over the course of several days, and then regrow during the 2 h return to euthermia. Similar structural changes take place in neurons from the hippocampus, cortex, and thalamus, suggesting a global phenomenon. Investigation of neural microstructure from groups of animals hibernating at different ambient temperatures revealed that there is a linear relationship between neural retraction and minimum body temperature. Despite significant temperature-dependent differences in extent of retraction during torpor, recovery reaches the same final values of cell body area, dendritic arbor complexity, and spine density. This study demonstrates large-scale and seemingly ubiquitous neural plasticity in the ground squirrel brain during torpor. It also defines a temperature-driven model of dramatic neural plasticity, which provides a unique opportunity to explore mechanisms of large-scale regrowth in adult mammals, and the effects of remodeling on learning and memory.
冬眠的哺乳动物能够在大脑温度接近冰点且神经活动几乎停止长达一周或更长时间的情况下存活，这一点十分引人注目。这种极端的生理状态与海马神经元的树突和突触变化有关。在此，我们研究这些变化是否是由温度驱动的、在整个大脑中普遍存在的现象。我们通过离子电渗法将荧光黄注入冬眠地松鼠固定脑片中的几种神经元类型。我们分析了处于两种不同环境温度下的几个蛰伏阶段以及夏季的动物的神经元微观结构。我们发现，冬眠地松鼠几种细胞类型的神经元细胞体、树突和棘在进入蛰伏状态时会收缩，在几天内变化不大，然后在恢复正常体温的2小时内重新生长。海马体、皮层和丘脑的神经元也发生了类似的结构变化，这表明这是一种普遍现象。对在不同环境温度下冬眠的动物群体的神经微观结构进行研究发现，神经收缩与最低体温之间存在线性关系。尽管在蛰伏期间收缩程度存在显著的温度依赖性差异，但恢复后细胞体面积、树突分支复杂性和棘密度的最终值相同。这项研究证明了地松鼠大脑在蛰伏期间存在大规模且似乎普遍存在的神经可塑性。它还定义了一种由温度驱动的显著神经可塑性模型，这为探索成年哺乳动物大规模再生的机制以及重塑对学习和记忆的影响提供了独特的机会。
