Elsevier

Experimental Neurology

Volume 230, Issue 2, August 2011, Pages 176-185
Experimental Neurology

Unilateral entorhinal denervation leads to long-lasting dendritic alterations of mouse hippocampal granule cells

https://doi.org/10.1016/j.expneurol.2011.04.011Get rights and content

Abstract

Following brain injury, neurons efferently connected from the lesion site are denervated and remodel their dendritic tree. Denervation-induced dendritic reorganization of granule cells was investigated in the dentate gyrus of the Thy1-GFP mouse. After mechanical transection of the perforant path, single granule cells were 3D-reconstructed at different time points post-lesion (3 d, 7 d, 10 d, 30 d, 90 d and 180 d) and their soma size, total dendritic length, number of dendritic segments and dendritic branch orders were studied. Changes in spine densities were determined using 3D-analysis of individual dendritic segments. Following entorhinal denervation the granule cell arbor progressively atrophied until 90 d post-lesion (reduction of total dendritic length to ~ 50% of control). Dendritic alterations occurred selectively in the denervated outer molecular layer, where a loss of distal dendritic segments and a reduction of mean segment length were seen. At 180 d post-lesion total dendritic length partially recovered (~ 70% of control). This recovery appeared to be the result of a re-elongation of surviving dendrites rather than dendritic re-branching, since the number of dendritic segments did not recover. In contrast to the protracted dendritic changes, spine density changes followed a faster time course. In the denervated layer spine densities dropped to ~ 65% of control values and fully recovered by 30 d post-lesion. We conclude that entorhinal denervation in mouse causes protracted and long-term structural alterations of the granule cell dendritic tree. Spontaneously occurring reinnervation processes, such as the sprouting of surviving afferent fibers, are insufficient to maintain the granule cell dendritic arbor.

Highlights

► Long-term survival study of dendritic remodeling after denervation in mouse. ► Denervation causes loss of distal dendritic segments and a reduction of mean segment length. ► Dendritic alterations are protracted and occur over the course of months. ► Denervation causes transient and layer-specific changes in spine density. ► Denervation has long-lasting effects on the complexity of the dendritic tree.

Section snippets

Animals and tissue preparation

Adult male Thy1-GFP transgenic mice (Thy1-GFP-M line; C57BL/6 background; Feng et al., 2000; N = 33; Fig. 1) housed under standard laboratory conditions were used. Experimental animals were divided into three groups: control animals 4–5 months (N = 5), control animals 11–12 months (N = 5) and animals with unilateral wire knife transections of the perforant path (N = 23). Animals were allowed to survive 3, 7, 10, 30, 90 and 180 d prior to morphological analysis (see Table 1 for details concerning number of

The fascia dentata of the normal (non-denervated) Thy1-GFP mouse

Using fluorescence microscopy, a subpopulation of intensely green-fluorescent granule cells was revealed in the fascia dentata of Thy1-GFP mice (Figs. 1A, B). These neurons were located in the granule cell layer and could be identified based on morphological criteria, i. e. small ovoid somata, apically oriented spiny dendrites extending all the way to the hippocampal fissure and a basally oriented axon originating from the granule cell soma and extending into the hilus (Desmond and Levy, 1982,

Discussion

In the present study, we investigated the reorganization of dentate granule cells after entorhinal denervation in Thy1-GFP mouse mutants. The main results are: (1) Entorhinal denervation caused a profound reorganization of the dendritic tree of dentate granule cells. Atrophic changes occurred primarily in the denervated zone of the molecular layer, where a significant shortening of dendrites and a loss of dendritic segments was seen. (2) Dendritic atrophy progressed until ~ 90 d post-lesion. By

Acknowledgments

The authors thank Anke Biczysko, Heike Korff, and Charlotte Nolte-Uhl for excellent technical support, Dr. Guoping Feng for providing the Thy1-GFP mice, and Dr. Peter Jedlicka for reading and commenting on the manuscript. Supported by Deutsche Forschungsgemeinschaft (DFG) and LOEWE Lipid Signaling Forschungszentrum Frankfurt (LiFF).

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    1

    These authors contributed equally to this work.

    2

    Present address: Max-Planck-Institute for Brain Research, Deutschordenstraße 46, 60528 Frankfurt am Main, Germany.

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