Limits...
Spatiotemporal dynamics of lesion-induced axonal sprouting and its relation to functional architecture of the cerebellum

View Article: PubMed Central - PubMed

ABSTRACT

Neurodegenerative lesions induce sprouting of new collaterals from surviving axons, but the extent to which this form of axonal remodelling alters brain functional structure remains unclear. To understand how collateral sprouting proceeds in the adult brain, we imaged post-lesion sprouting of cerebellar climbing fibres (CFs) in mice using in vivo time-lapse microscopy. Here we show that newly sprouted CF collaterals innervate multiple Purkinje cells (PCs) over several months, with most innervations emerging at 3–4 weeks post lesion. Simultaneous imaging of cerebellar functional structure reveals that surviving CFs similarly innervate functionally relevant and non-relevant PCs, but have more synaptic area on PCs near the collateral origin than on distant PCs. These results suggest that newly sprouted axon collaterals do not preferentially innervate functionally relevant postsynaptic targets. Nonetheless, the spatial gradient of collateral innervation might help to loosely maintain functional synaptic circuits if functionally relevant neurons are clustered in the lesioned area.

No MeSH data available.


Related in: MedlinePlus

CF morphology in the normal cerebellum and CF collateral sprouting induced by 3-AP injection into the inferior olive.(a) Image of normal CFs in vivo from a Nefl-EGFP tg mouse (no 3-AP injection) as viewed from a window placed over lobule VII of cerebellar cortex using two-photon microscopy. All in vivo images (a,c,d) are maximum projections showing top-down views of CFs in the molecular layer. Scale bar, 100 μm. (b) Image of normal CFs in a fixed cerebellar slice from a Nefl-GFP tg mouse. View of CFs in the molecular layer in para-sagittal plane (left) and view of another CF in transverse plane (right). (c) Image of a CF ladder in vivo (left) and its trace (right) in which red line represents the main stalk and the blue lines emerging from the main stalk represent the rungs of the CF ladder. (d) A representative image of surviving CFs in vivo from a Nefl-EGFP tg mice 1 week after 3-AP injection as viewed from a window placed over lobule VII of cerebellar cortex using two-photon microscopy. (Left) Red square shows site of collateral sprouting magnified in the images on the right. (Right) Red arrows mark collaterals in the magnified view. As shown in this example, collateral sprouting was observed 1 week after 3-AP injection in all animals (n=12). Scale bar, 50 μm. (e) Immunolabelling of synaptic sites with VGLUT2 (red) in CFs (anti-GFP, cyan) 2 weeks after 3-AP injection (n=2 animals). The molecular layer of lobule VIII in a fixed coronal section is shown. Red square shows site of collateral sprouting magnified in the images on the right. Note that new CF ladders (white arrowheads) are all VGLUT2-positive regardless of their ladder length and distance from their origin. Scale bar, 50 μm.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
getmorefigures.php?uid=PMC5036008&req=5

f1: CF morphology in the normal cerebellum and CF collateral sprouting induced by 3-AP injection into the inferior olive.(a) Image of normal CFs in vivo from a Nefl-EGFP tg mouse (no 3-AP injection) as viewed from a window placed over lobule VII of cerebellar cortex using two-photon microscopy. All in vivo images (a,c,d) are maximum projections showing top-down views of CFs in the molecular layer. Scale bar, 100 μm. (b) Image of normal CFs in a fixed cerebellar slice from a Nefl-GFP tg mouse. View of CFs in the molecular layer in para-sagittal plane (left) and view of another CF in transverse plane (right). (c) Image of a CF ladder in vivo (left) and its trace (right) in which red line represents the main stalk and the blue lines emerging from the main stalk represent the rungs of the CF ladder. (d) A representative image of surviving CFs in vivo from a Nefl-EGFP tg mice 1 week after 3-AP injection as viewed from a window placed over lobule VII of cerebellar cortex using two-photon microscopy. (Left) Red square shows site of collateral sprouting magnified in the images on the right. (Right) Red arrows mark collaterals in the magnified view. As shown in this example, collateral sprouting was observed 1 week after 3-AP injection in all animals (n=12). Scale bar, 50 μm. (e) Immunolabelling of synaptic sites with VGLUT2 (red) in CFs (anti-GFP, cyan) 2 weeks after 3-AP injection (n=2 animals). The molecular layer of lobule VIII in a fixed coronal section is shown. Red square shows site of collateral sprouting magnified in the images on the right. Note that new CF ladders (white arrowheads) are all VGLUT2-positive regardless of their ladder length and distance from their origin. Scale bar, 50 μm.

Mentions: We first determined the spatiotemporal pattern of CF collateral sprouting in adult mice. To visualize CFs, we used a transgenic mouse line in which EGFP is expressed under the neurofilament light chain promoter (Nefl-EGFP tg mice). As shown in our previous study19, ∼80% of CFs in the cerebellar vermis were labelled with EGFP in Nefl-EGFP tg mice (Fig. 1a). In the mature cerebellum, a single CF normally innervates only one PC and closely follows its dendritic arbor attaining an expansive appearance in the para-sagittal plane (Fig. 1b, left). In the transverse plane, because of the planarity of the PC dendritic arbor, the CFs have a restricted spread giving them a ladder-like appearance (Fig. 1b, right) with a thick main stalk and thinner rungs extending from the main stalk (Fig. 1c). This ladder-like structure represents the appearance of CFs in our in vivo time-lapse images. We refer to this ladder-like structure as a CF ladder hereafter.


Spatiotemporal dynamics of lesion-induced axonal sprouting and its relation to functional architecture of the cerebellum
CF morphology in the normal cerebellum and CF collateral sprouting induced by 3-AP injection into the inferior olive.(a) Image of normal CFs in vivo from a Nefl-EGFP tg mouse (no 3-AP injection) as viewed from a window placed over lobule VII of cerebellar cortex using two-photon microscopy. All in vivo images (a,c,d) are maximum projections showing top-down views of CFs in the molecular layer. Scale bar, 100 μm. (b) Image of normal CFs in a fixed cerebellar slice from a Nefl-GFP tg mouse. View of CFs in the molecular layer in para-sagittal plane (left) and view of another CF in transverse plane (right). (c) Image of a CF ladder in vivo (left) and its trace (right) in which red line represents the main stalk and the blue lines emerging from the main stalk represent the rungs of the CF ladder. (d) A representative image of surviving CFs in vivo from a Nefl-EGFP tg mice 1 week after 3-AP injection as viewed from a window placed over lobule VII of cerebellar cortex using two-photon microscopy. (Left) Red square shows site of collateral sprouting magnified in the images on the right. (Right) Red arrows mark collaterals in the magnified view. As shown in this example, collateral sprouting was observed 1 week after 3-AP injection in all animals (n=12). Scale bar, 50 μm. (e) Immunolabelling of synaptic sites with VGLUT2 (red) in CFs (anti-GFP, cyan) 2 weeks after 3-AP injection (n=2 animals). The molecular layer of lobule VIII in a fixed coronal section is shown. Red square shows site of collateral sprouting magnified in the images on the right. Note that new CF ladders (white arrowheads) are all VGLUT2-positive regardless of their ladder length and distance from their origin. Scale bar, 50 μm.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC5036008&req=5

f1: CF morphology in the normal cerebellum and CF collateral sprouting induced by 3-AP injection into the inferior olive.(a) Image of normal CFs in vivo from a Nefl-EGFP tg mouse (no 3-AP injection) as viewed from a window placed over lobule VII of cerebellar cortex using two-photon microscopy. All in vivo images (a,c,d) are maximum projections showing top-down views of CFs in the molecular layer. Scale bar, 100 μm. (b) Image of normal CFs in a fixed cerebellar slice from a Nefl-GFP tg mouse. View of CFs in the molecular layer in para-sagittal plane (left) and view of another CF in transverse plane (right). (c) Image of a CF ladder in vivo (left) and its trace (right) in which red line represents the main stalk and the blue lines emerging from the main stalk represent the rungs of the CF ladder. (d) A representative image of surviving CFs in vivo from a Nefl-EGFP tg mice 1 week after 3-AP injection as viewed from a window placed over lobule VII of cerebellar cortex using two-photon microscopy. (Left) Red square shows site of collateral sprouting magnified in the images on the right. (Right) Red arrows mark collaterals in the magnified view. As shown in this example, collateral sprouting was observed 1 week after 3-AP injection in all animals (n=12). Scale bar, 50 μm. (e) Immunolabelling of synaptic sites with VGLUT2 (red) in CFs (anti-GFP, cyan) 2 weeks after 3-AP injection (n=2 animals). The molecular layer of lobule VIII in a fixed coronal section is shown. Red square shows site of collateral sprouting magnified in the images on the right. Note that new CF ladders (white arrowheads) are all VGLUT2-positive regardless of their ladder length and distance from their origin. Scale bar, 50 μm.
Mentions: We first determined the spatiotemporal pattern of CF collateral sprouting in adult mice. To visualize CFs, we used a transgenic mouse line in which EGFP is expressed under the neurofilament light chain promoter (Nefl-EGFP tg mice). As shown in our previous study19, ∼80% of CFs in the cerebellar vermis were labelled with EGFP in Nefl-EGFP tg mice (Fig. 1a). In the mature cerebellum, a single CF normally innervates only one PC and closely follows its dendritic arbor attaining an expansive appearance in the para-sagittal plane (Fig. 1b, left). In the transverse plane, because of the planarity of the PC dendritic arbor, the CFs have a restricted spread giving them a ladder-like appearance (Fig. 1b, right) with a thick main stalk and thinner rungs extending from the main stalk (Fig. 1c). This ladder-like structure represents the appearance of CFs in our in vivo time-lapse images. We refer to this ladder-like structure as a CF ladder hereafter.

View Article: PubMed Central - PubMed

ABSTRACT

Neurodegenerative lesions induce sprouting of new collaterals from surviving axons, but the extent to which this form of axonal remodelling alters brain functional structure remains unclear. To understand how collateral sprouting proceeds in the adult brain, we imaged post-lesion sprouting of cerebellar climbing fibres (CFs) in mice using in vivo time-lapse microscopy. Here we show that newly sprouted CF collaterals innervate multiple Purkinje cells (PCs) over several months, with most innervations emerging at 3–4 weeks post lesion. Simultaneous imaging of cerebellar functional structure reveals that surviving CFs similarly innervate functionally relevant and non-relevant PCs, but have more synaptic area on PCs near the collateral origin than on distant PCs. These results suggest that newly sprouted axon collaterals do not preferentially innervate functionally relevant postsynaptic targets. Nonetheless, the spatial gradient of collateral innervation might help to loosely maintain functional synaptic circuits if functionally relevant neurons are clustered in the lesioned area.

No MeSH data available.


Related in: MedlinePlus