Reversible reduction in dendritic spines in CA1 of rat and ground squirrel subjected to hypothermia-normothermia in vivo: A three-dimensional electron microscope study.
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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ABSTRACT: Seasonal affective disorder (SAD) is characterized by depressive episodes during winter that are alleviated during summer and by morning bright light treatment. Currently, there is no animal model of SAD. However, it may be possible to use rodents that respond to day length to understand how day length can shape brain and behavior in humans. For instance, Siberian hamsters use day length to time seasonal cycles of reproduction and also exhibit changes in nonreproductive behaviors dependent on day length. Specifically, short-day Siberian hamsters increase floating in the forced swim test (a behavioral test used to screen antidepressant compounds). Current research in depression and animal models of depression suggests that hippocampal atrophy may underlie the symptoms of depression and depressive-like behaviors, respectively. The goal of this study was to determine whether altered depressive-like responses after exposure to short days are associated with photoperiod-mediated plasticity within the hippocampus of Siberian hamsters. Hamsters were housed in either short (8:16 LD) or long days (16:8 LD) for 10 weeks. At the end of 10 weeks hamsters were tested in the forced swim test and 48 h later, brains were removed and stained using the Golgi impregnation method. Brains were processed for hippocampal dendritic length, branching, and spines, as well as cell body size. Short days significantly reduced cell body size and dendritic complexity in the CA1 region of the hippocampus. This suggests that altered depressive-like behavior induced by exposure to short days may be a consequence of reduced complexity (and perhaps connectivity) in the hippocampus.
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ABSTRACT: Morphometric methods were used to study the ultrastructure of afferent synapses on the ventral dendrites of Mauthner neurons (MN) during adaptation of goldfish to prolonged, fatiguing, sensory (visual) stimu- lation inducing increased resistance of MN. The extent of active zones (AZ) in synapses located on the MN ventral dendrite was found to decrease significantly, by 23%, after adaptation. The extent of the AZ of excitatory visual synapses decreased by 29% as compared with controls, with a simultaneous 71% increase in the extent of desmosome-like contacts (DLC) bordering AZ. There was also a 19% reduction in the extent of AZ of inhibitory synapses after adaptation, which is consistent with the important role of inhibitory processes in sensory pathways during memory formation. Considering the actin nature of DLC, it can be suggested that adaptation to visual stimulation is based on a synaptic mechanism of regulation of neurotransmitter secretion by actin.Neuroscience and Behavioral Physiology 05/2014; 44(4):461-466.
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ABSTRACT: Why do neurons have dendritic spines? This question-the heart of what Yuste calls "the spine problem"-presupposes that why-questions of this sort have scientific answers: that empirical findings can favor or count against claims about why neurons have spines. Here we show how such questions can receive empirical answers. We construe such why-questions as questions about how spines make a difference to the behavior of some mechanism that we take to be significant. Why-questions are driven fundamentally by the effort to understand how some item, such as the dendritic spine, is situated in the causal structure of the world (the causal nexus). They ask for a filter on that busy world that allows us to see a part's individual contribution to a mechanism, independent of everything else going on. So understood, answers to why-questions can be assessed by testing the claims these answers make about the causal structure of a mechanism. We distinguish four ways of making a difference to a mechanism (necessary, modulatory, component, background condition), and we sketch their evidential requirements. One consequence of our analysis is that there are many spine problems and that any given spine problem might have many acceptable answers.Frontiers in Neuroanatomy 09/2014; 8:95. DOI:10.3389/fnana.2014.00095 · 4.18 Impact Factor