Article

Reversible reduction in dendritic spines in CA1 of rat and ground squirrel subjected to hypothermia-normothermia in vivo: A three-dimensional electron microscope study.

The Open University, Department of Biological Sciences, Faculty of Sciences, Walton Hall, Milton Keynes MK7 6AA, UK.
Neuroscience (Impact Factor: 3.33). 12/2007; 149(3):549-60. DOI: 10.1016/j.neuroscience.2007.07.059
Source: PubMed

ABSTRACT A study was made at electron microscope level of changes in the three-dimensional (3-D) morphology of dendritic spines and postsynaptic densities (PSDs) in CA1 of the hippocampus in ground squirrels, taken either at low temperature during hibernation (brain temperature 2-4 degrees C), or after warming and recovery to the normothermic state (34 degrees C). In addition, the morphology of PSDs and spines was measured in a non-hibernating mammal, rat, subjected to cooling at 2 degrees C at which time core rectal temperature was 15 degrees C, and then after warming to normothermic conditions. Significant differences were found in the proportion of thin and stubby spines, and shaft synapses in CA1 for rats and ground squirrels for normothermia compared with cooling or hibernation. Hypothermia induced a decrease in the proportion of thin spines, and an increase in stubby and shaft spines, but no change in the proportion of mushroom spines. The changes in redistribution of these three categories of spines in ground squirrel are more prominent than in rat. There were no significant differences in synapse density determined for ground squirrels or rats at normal compared with low temperature. Measurement of spine and PSD volume (for mushroom and thin spines) also showed no significant differences between the two functional states in either rats or ground squirrels, nor were there any differences in distances between neighboring synapses. Spinules on dendritic shafts were notable qualitatively during hibernation, but absent in normothermia. These data show that hypothermia results in morphological changes which are essentially similar in both a hibernating and a non-hibernating animal.

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    • "These changes have been characterized in other species of ground squirrels and include: a large decrease in pyramidal cell soma size [53] [54] [55], decreases in dendritic branching and spine density of CA1 and CA3 cells [53] [54] [55], fewer mossy fiber terminals [56] [57] and up to a 65% loss of synapses [58] [59]. Upon arousal from hibernation, there is a rapid increase in cell soma size, dendritic branching and spine density within several hours [53] [54] [57] [58] and this appears to parallel a recovery of function based on behavioral tests [60]. However, none of these studies examined sex as a variable. "
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    • "Most hibernators periodically interrupt the state of hibernation (torpor) by euthermic episodes or arousal, a process responsible for up to 90% of the energy consumed during hibernation. Previously, using Golgi and electron microscope studies in hippocampal tissue of hibernating ground squirrels we have shown marked structural alterations in the components of neural circuitry, with the reversible retraction of dendritic spines and synapses in CA1 and CA3 [1] [2]. "
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    • "Recent electron-microscopic data indicate that spine-pruned cortical neurons do lose their connection with afferent inputs (Knott et al., 2006). On the other hand, in hibernating animals there is a marked decrease in spine density during hibernation but there is an increase in shaft synapses (Popov et al., 2007; von der Ohe et al., 2006), and when the animals wake up from hibernation they regain the spines and appear to remember tasks learnt before hibernation, indicating that regardless of the persistence of spines, memories are retained (Clemens et al., 2009). In fact, if trained 24 h after arousal from hibernation, they remember better than controls (Weltzin et al., 2006). "
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