Elsevier

Neuroscience

Volume 149, Issue 3, 9 November 2007, Pages 549-560
Neuroscience

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

https://doi.org/10.1016/j.neuroscience.2007.07.059Get rights and content

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 °C), or after warming and recovery to the normothermic state (34 °C). In addition, the morphology of PSDs and spines was measured in a non-hibernating mammal, rat, subjected to cooling at 2 °C at which time core rectal temperature was 15 °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.

Section snippets

Ground squirrels

Adult ground squirrels, Spermophilus undulatus, of both sexes and 600–700 g in weight, were caught in Yakutiya (Siberia) and kept in individual cages in a cold vivarium under natural photoperiodicity. Food supplemented with sunflower seeds and carrots, and nesting material was provided ad libitum. In November, the animals were individually placed in wooden hibernation boxes (20×20×25 cm) and transferred to a dark room having a temperature of 1–3 °C. Food was not provided during hibernation.

Synapse density

Each synapse was identified primarily on the basis of prominent PSDs and synaptic vesicles clustered close to the apposition zone. Using a volume disector synaptic densities were expressed as number of synapses identified per 100 um3 to tissue as in (Harris 1994, Fiala et al 1998, Popov et al 2004). Fig. 2 shows synapse density for both rats and ground squirrels. There are no significant differences for either functional state of rats (normothermia: 329 synapses±38; Cooling: 327±8; Recovery:

Discussion

The data presented show clearly that significant morphological changes in dendritic spines occur in both a hibernating (ground squirrel) and non-hibernating mammal (rat), subjected to low temperature. Thin dendritic spines decrease as a percentage of the population measured and there is a concomitant increase in the percentages of both stubby spines and synapses directly on dendritic shafts. Recovery on warming is similar in both animals, with reversion to the spine proportions observed before

Acknowledgments

Supported by EU FPVI Promemoria Contract No. 512012 and to V.I.P. (RFBR grant 05-04-49635-a).

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