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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.

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Spatiotemporal pattern of CF collateral sprouting in the double-transgenic mice.(a) Average number of ladders categorized as outside added (±s.e.m.) at each time point (n=8 surviving CFs from 3 double-transgenic mice, black). The data from single transgenic mice (green, taken from Fig. 2b) are overlaid for comparison. No interaction or genotype or time point effect was found (two-way repeated measures analysis of variance (ANOVA): F(6,30)=1.197; P=0.4). (b) Average number of ladders categorized as inside added (±s.e.m.) at each time point (n=8 surviving CFs from 3 double-transgenic mice, black). The data from single-transgenic mice (green, taken from Fig. 2b) are overlaid for comparison. No interaction or genotype effect was found, however time points did have a significant effect (two-way repeated measures ANOVA: F(6,30)=3.125; P=0.01). (c,d) Representative images showing CF collaterals crossing the zonal boundary in lobule VIII. In vivo two-photon image of the same area of cerebellar cortex taken 5/6 weeks apart. Maximum projections (top-down view) of the CFs and the zonal boundary in the molecular layer are shown. Scale bar, 50 μm. (e) Average change in stalk length (±s.e.m.) of ladders growing in native (red, n=49 ladders) and non-native (black, n=32 ladders) zones at each time point, where each time point indicates number of weeks from birth of the ladder. The change in stalk length was significantly different over time for ladders growing in their native or non-native zone (one-way ANOVA with Tukey post hoc analysis: native zone; F(5,116)=7.19, P<0.0001, *P<0.001 compared with time points 1, 2, 3, 4 and 5; and non-native zone; F(5,99)=17.5, P<0.0001, *P<0.001 compared with time points 1, 2, 3, 4 and 5). (f) Average change in total ladder length (±s.e.m.) of ladders growing in native (red, n=49 ladders) and non-native (black, n=32 ladders) zones at each time point, where each time point indicates number of weeks from birth of the ladder. The change in total ladder length was significantly different over time for ladders growing in their native or non-native zone (one-way ANOVA with Tukey post hoc analysis: native zone; F(5,116)=7.667, P<0.0001, *P<0.001 compared with time points 1, 2 and 3; and non-native zone; F(5,99)=8.137, P<0.0001, *P<0.001 compared with time points 1, 2, 3 and 4).
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f5: Spatiotemporal pattern of CF collateral sprouting in the double-transgenic mice.(a) Average number of ladders categorized as outside added (±s.e.m.) at each time point (n=8 surviving CFs from 3 double-transgenic mice, black). The data from single transgenic mice (green, taken from Fig. 2b) are overlaid for comparison. No interaction or genotype or time point effect was found (two-way repeated measures analysis of variance (ANOVA): F(6,30)=1.197; P=0.4). (b) Average number of ladders categorized as inside added (±s.e.m.) at each time point (n=8 surviving CFs from 3 double-transgenic mice, black). The data from single-transgenic mice (green, taken from Fig. 2b) are overlaid for comparison. No interaction or genotype effect was found, however time points did have a significant effect (two-way repeated measures ANOVA: F(6,30)=3.125; P=0.01). (c,d) Representative images showing CF collaterals crossing the zonal boundary in lobule VIII. In vivo two-photon image of the same area of cerebellar cortex taken 5/6 weeks apart. Maximum projections (top-down view) of the CFs and the zonal boundary in the molecular layer are shown. Scale bar, 50 μm. (e) Average change in stalk length (±s.e.m.) of ladders growing in native (red, n=49 ladders) and non-native (black, n=32 ladders) zones at each time point, where each time point indicates number of weeks from birth of the ladder. The change in stalk length was significantly different over time for ladders growing in their native or non-native zone (one-way ANOVA with Tukey post hoc analysis: native zone; F(5,116)=7.19, P<0.0001, *P<0.001 compared with time points 1, 2, 3, 4 and 5; and non-native zone; F(5,99)=17.5, P<0.0001, *P<0.001 compared with time points 1, 2, 3, 4 and 5). (f) Average change in total ladder length (±s.e.m.) of ladders growing in native (red, n=49 ladders) and non-native (black, n=32 ladders) zones at each time point, where each time point indicates number of weeks from birth of the ladder. The change in total ladder length was significantly different over time for ladders growing in their native or non-native zone (one-way ANOVA with Tukey post hoc analysis: native zone; F(5,116)=7.667, P<0.0001, *P<0.001 compared with time points 1, 2 and 3; and non-native zone; F(5,99)=8.137, P<0.0001, *P<0.001 compared with time points 1, 2, 3 and 4).

Mentions: The temporal pattern of collateral sprouting and ladder addition in the double-transgenic mice was similar to that in the single-transgenic mice (Fig. 5a,b, n=3 animals, only animals that had sufficient time points were quantitatively analysed). Inside ladder addition peaked at 4 weeks after the lesion, and most inside and outside additions were made within the first 4 weeks (Fig. 5b, number of ladders added in the first 4 weeks/total ladders analysed: single transgenic=49/101, double transgenic=40/96), suggesting that this temporal profile is preserved across the different lobules. Consistent with our observation from the single-transgenic data, the outside ladder addition did not stop even at 13 weeks post lesion in the double-transgenic mice. More importantly, these newly sprouted ladders added to the outside of the mediolateral extent of the parent CF allowed the parent CF to expand across the boundary of zebrin II stripes, from its original native zone, which is the zebrin II-positive or -negative zone it exists in, into the adjacent non-native zone (Fig. 5c,d). In Fig. 5c, two surviving CFs extend collaterals into adjacent non-native zone, but in Fig. 5d, only one of the two surviving CFs (upper right) poised at the zonal boundary extends a collateral into the non-native zone. In all six double-transgenic animals imaged (including three animals that were excluded from quantitative analysis), some surviving CFs ignored the zonal boundary. Although it is unclear why only a certain subset of surviving CFs extends into a non-native zone, these data show that the zonal boundary defined by zebrin II expression does not prevent new collaterals from extending into a non-native zone and giving rise to CF ladders in that non-native zone. Furthermore, CF ladders in native and non-native zones both expressed VGLUT2, suggesting that newly formed CF ladders were functional presynaptic terminals regardless of the zones they appeared in (Supplementary Fig. 4).


Spatiotemporal dynamics of lesion-induced axonal sprouting and its relation to functional architecture of the cerebellum
Spatiotemporal pattern of CF collateral sprouting in the double-transgenic mice.(a) Average number of ladders categorized as outside added (±s.e.m.) at each time point (n=8 surviving CFs from 3 double-transgenic mice, black). The data from single transgenic mice (green, taken from Fig. 2b) are overlaid for comparison. No interaction or genotype or time point effect was found (two-way repeated measures analysis of variance (ANOVA): F(6,30)=1.197; P=0.4). (b) Average number of ladders categorized as inside added (±s.e.m.) at each time point (n=8 surviving CFs from 3 double-transgenic mice, black). The data from single-transgenic mice (green, taken from Fig. 2b) are overlaid for comparison. No interaction or genotype effect was found, however time points did have a significant effect (two-way repeated measures ANOVA: F(6,30)=3.125; P=0.01). (c,d) Representative images showing CF collaterals crossing the zonal boundary in lobule VIII. In vivo two-photon image of the same area of cerebellar cortex taken 5/6 weeks apart. Maximum projections (top-down view) of the CFs and the zonal boundary in the molecular layer are shown. Scale bar, 50 μm. (e) Average change in stalk length (±s.e.m.) of ladders growing in native (red, n=49 ladders) and non-native (black, n=32 ladders) zones at each time point, where each time point indicates number of weeks from birth of the ladder. The change in stalk length was significantly different over time for ladders growing in their native or non-native zone (one-way ANOVA with Tukey post hoc analysis: native zone; F(5,116)=7.19, P<0.0001, *P<0.001 compared with time points 1, 2, 3, 4 and 5; and non-native zone; F(5,99)=17.5, P<0.0001, *P<0.001 compared with time points 1, 2, 3, 4 and 5). (f) Average change in total ladder length (±s.e.m.) of ladders growing in native (red, n=49 ladders) and non-native (black, n=32 ladders) zones at each time point, where each time point indicates number of weeks from birth of the ladder. The change in total ladder length was significantly different over time for ladders growing in their native or non-native zone (one-way ANOVA with Tukey post hoc analysis: native zone; F(5,116)=7.667, P<0.0001, *P<0.001 compared with time points 1, 2 and 3; and non-native zone; F(5,99)=8.137, P<0.0001, *P<0.001 compared with time points 1, 2, 3 and 4).
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f5: Spatiotemporal pattern of CF collateral sprouting in the double-transgenic mice.(a) Average number of ladders categorized as outside added (±s.e.m.) at each time point (n=8 surviving CFs from 3 double-transgenic mice, black). The data from single transgenic mice (green, taken from Fig. 2b) are overlaid for comparison. No interaction or genotype or time point effect was found (two-way repeated measures analysis of variance (ANOVA): F(6,30)=1.197; P=0.4). (b) Average number of ladders categorized as inside added (±s.e.m.) at each time point (n=8 surviving CFs from 3 double-transgenic mice, black). The data from single-transgenic mice (green, taken from Fig. 2b) are overlaid for comparison. No interaction or genotype effect was found, however time points did have a significant effect (two-way repeated measures ANOVA: F(6,30)=3.125; P=0.01). (c,d) Representative images showing CF collaterals crossing the zonal boundary in lobule VIII. In vivo two-photon image of the same area of cerebellar cortex taken 5/6 weeks apart. Maximum projections (top-down view) of the CFs and the zonal boundary in the molecular layer are shown. Scale bar, 50 μm. (e) Average change in stalk length (±s.e.m.) of ladders growing in native (red, n=49 ladders) and non-native (black, n=32 ladders) zones at each time point, where each time point indicates number of weeks from birth of the ladder. The change in stalk length was significantly different over time for ladders growing in their native or non-native zone (one-way ANOVA with Tukey post hoc analysis: native zone; F(5,116)=7.19, P<0.0001, *P<0.001 compared with time points 1, 2, 3, 4 and 5; and non-native zone; F(5,99)=17.5, P<0.0001, *P<0.001 compared with time points 1, 2, 3, 4 and 5). (f) Average change in total ladder length (±s.e.m.) of ladders growing in native (red, n=49 ladders) and non-native (black, n=32 ladders) zones at each time point, where each time point indicates number of weeks from birth of the ladder. The change in total ladder length was significantly different over time for ladders growing in their native or non-native zone (one-way ANOVA with Tukey post hoc analysis: native zone; F(5,116)=7.667, P<0.0001, *P<0.001 compared with time points 1, 2 and 3; and non-native zone; F(5,99)=8.137, P<0.0001, *P<0.001 compared with time points 1, 2, 3 and 4).
Mentions: The temporal pattern of collateral sprouting and ladder addition in the double-transgenic mice was similar to that in the single-transgenic mice (Fig. 5a,b, n=3 animals, only animals that had sufficient time points were quantitatively analysed). Inside ladder addition peaked at 4 weeks after the lesion, and most inside and outside additions were made within the first 4 weeks (Fig. 5b, number of ladders added in the first 4 weeks/total ladders analysed: single transgenic=49/101, double transgenic=40/96), suggesting that this temporal profile is preserved across the different lobules. Consistent with our observation from the single-transgenic data, the outside ladder addition did not stop even at 13 weeks post lesion in the double-transgenic mice. More importantly, these newly sprouted ladders added to the outside of the mediolateral extent of the parent CF allowed the parent CF to expand across the boundary of zebrin II stripes, from its original native zone, which is the zebrin II-positive or -negative zone it exists in, into the adjacent non-native zone (Fig. 5c,d). In Fig. 5c, two surviving CFs extend collaterals into adjacent non-native zone, but in Fig. 5d, only one of the two surviving CFs (upper right) poised at the zonal boundary extends a collateral into the non-native zone. In all six double-transgenic animals imaged (including three animals that were excluded from quantitative analysis), some surviving CFs ignored the zonal boundary. Although it is unclear why only a certain subset of surviving CFs extends into a non-native zone, these data show that the zonal boundary defined by zebrin II expression does not prevent new collaterals from extending into a non-native zone and giving rise to CF ladders in that non-native zone. Furthermore, CF ladders in native and non-native zones both expressed VGLUT2, suggesting that newly formed CF ladders were functional presynaptic terminals regardless of the zones they appeared in (Supplementary Fig. 4).

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&ndash;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