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Pre-existing astrocytes form functional perisynaptic processes on neurons generated in the adult hippocampus.

Krzisch M, Temprana SG, Mongiat LA, Armida J, Schmutz V, Virtanen MA, Kocher-Braissant J, Kraftsik R, Vutskits L, Conzelmann KK, Bergami M, Gage FH, Schinder AF, Toni N - Brain Struct Funct (2014)

Bottom Line: We found that the afferent and efferent synapses of newborn neurons are ensheathed by astrocytic processes, irrespective of the age of the neurons or the size of their synapses.Finally, some processes were found intercalated between newly formed dendritic spines and potential presynaptic partners, suggesting that they may also play a structural role in the connectivity of new spines.Together, these results indicate that pre-existing astrocytes remodel their processes to ensheathe synapses of adult-born neurons and participate to the functional and structural integration of these cells into the hippocampal network.

View Article: PubMed Central - PubMed

Affiliation: Department of Fundamental Neurosciences, University of Lausanne, 9 rue du Bugnon, 1005, Lausanne, Switzerland.

ABSTRACT
The adult dentate gyrus produces new neurons that morphologically and functionally integrate into the hippocampal network. In the adult brain, most excitatory synapses are ensheathed by astrocytic perisynaptic processes that regulate synaptic structure and function. However, these processes are formed during embryonic or early postnatal development and it is unknown whether astrocytes can also ensheathe synapses of neurons born during adulthood and, if so, whether they play a role in their synaptic transmission. Here, we used a combination of serial-section immuno-electron microscopy, confocal microscopy, and electrophysiology to examine the formation of perisynaptic processes on adult-born neurons. We found that the afferent and efferent synapses of newborn neurons are ensheathed by astrocytic processes, irrespective of the age of the neurons or the size of their synapses. The quantification of gliogenesis and the distribution of astrocytic processes on synapses formed by adult-born neurons suggest that the majority of these processes are recruited from pre-existing astrocytes. Furthermore, the inhibition of astrocytic glutamate re-uptake significantly reduced postsynaptic currents and increased paired-pulse facilitation in adult-born neurons, suggesting that perisynaptic processes modulate synaptic transmission on these cells. Finally, some processes were found intercalated between newly formed dendritic spines and potential presynaptic partners, suggesting that they may also play a structural role in the connectivity of new spines. Together, these results indicate that pre-existing astrocytes remodel their processes to ensheathe synapses of adult-born neurons and participate to the functional and structural integration of these cells into the hippocampal network.

No MeSH data available.


Related in: MedlinePlus

Astrocytic perisynaptic processes ensheathe dendritic spines of adult-born neurons. aLeft RABV used for trans-synaptic tracing reveals astrocytes: Mice were infected with a MoMuLV expressing DsRed, protein G and TVA. Five weeks later, they were infected with RABV expressing GFP and examined 1 week later. Confocal micrograph maximal projection reveals GFP-labeled astrocytes (arrows) contacting a starter neuron (yellow) co-infected by MoMuLV and RABV. Presumable presynaptic neurons (RABV-only infected) are also labeled in green. Scale bar 20 µm. Right higher magnification single optical section micrograph showing the dendrite of a starter neuron (yellow) in close contact with GFP-labeled astrocytic processes. Scale bar 5 µm. b Three-dimensional reconstruction of a synapse between a dendritic spine (red) and an axon terminal (blue) ensheathed by an astrocytic perisynaptic process (green). Scale bar 0.25 µm. c Proportion of the different types of astrocytic ensheathement on spines of adult-born neuron synapses (left) and GFP-negative, control neurons (right). d Mean perisynaptic ensheathement on spines of different morphologies on adult-born neurons (Kruskal–Wallis test, p < 0.05, n = 50–100 spines per group). e Mean perisynaptic ensheathement on spines of different morphologies on control neurons (Kruskal–Wallis test, p < 0.05, n = 50–100 spines per group). F filopodia, T thin spines, M mushroom spines. f Electron micrographs of dendritic spines from newborn neurons (false-colored in red) and axon terminals (blue) ensheathed by an astrocytic perisynaptic process (green). From left to right: the perisynaptic process is found on the axon terminal only, on the dendritic spine only, on both synaptic partners or is absent. Scale bars 0.25 µm. gLeft panel confocal micrograph maximal projection of an adult-born neuron (red) in the dentate gyrus of an Aldh1l1-GFP mouse, 4 weeks post-injection. Scale bar 20 µm. Right panel confocal micrograph single optical section (after deconvolution) of a dendrite of a newborn neuron (red) in the dentate gyrus of an Aldh1l1-GFP mouse 4 weeks post-injection. Scale bar 2 µm. h. Confocal micrographs of dendritic spines with astrocytic processes scored in four classes: score 0 no coverage, score 1 coverage inferior or equal to 25 % of the spine head, score 2 coverage between 25 and 50 %, score 3 coverage above 50 %. Scale bar 0.5 µm. i Histogram of the mean perisynaptic ensheathement on neurons of different ages, as assessed by confocal microscopy [One-way ANOVA between groups, F(3,71) = 1.18, p = 0.32, n = 84–1,780 spines per group]
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Fig1: Astrocytic perisynaptic processes ensheathe dendritic spines of adult-born neurons. aLeft RABV used for trans-synaptic tracing reveals astrocytes: Mice were infected with a MoMuLV expressing DsRed, protein G and TVA. Five weeks later, they were infected with RABV expressing GFP and examined 1 week later. Confocal micrograph maximal projection reveals GFP-labeled astrocytes (arrows) contacting a starter neuron (yellow) co-infected by MoMuLV and RABV. Presumable presynaptic neurons (RABV-only infected) are also labeled in green. Scale bar 20 µm. Right higher magnification single optical section micrograph showing the dendrite of a starter neuron (yellow) in close contact with GFP-labeled astrocytic processes. Scale bar 5 µm. b Three-dimensional reconstruction of a synapse between a dendritic spine (red) and an axon terminal (blue) ensheathed by an astrocytic perisynaptic process (green). Scale bar 0.25 µm. c Proportion of the different types of astrocytic ensheathement on spines of adult-born neuron synapses (left) and GFP-negative, control neurons (right). d Mean perisynaptic ensheathement on spines of different morphologies on adult-born neurons (Kruskal–Wallis test, p < 0.05, n = 50–100 spines per group). e Mean perisynaptic ensheathement on spines of different morphologies on control neurons (Kruskal–Wallis test, p < 0.05, n = 50–100 spines per group). F filopodia, T thin spines, M mushroom spines. f Electron micrographs of dendritic spines from newborn neurons (false-colored in red) and axon terminals (blue) ensheathed by an astrocytic perisynaptic process (green). From left to right: the perisynaptic process is found on the axon terminal only, on the dendritic spine only, on both synaptic partners or is absent. Scale bars 0.25 µm. gLeft panel confocal micrograph maximal projection of an adult-born neuron (red) in the dentate gyrus of an Aldh1l1-GFP mouse, 4 weeks post-injection. Scale bar 20 µm. Right panel confocal micrograph single optical section (after deconvolution) of a dendrite of a newborn neuron (red) in the dentate gyrus of an Aldh1l1-GFP mouse 4 weeks post-injection. Scale bar 2 µm. h. Confocal micrographs of dendritic spines with astrocytic processes scored in four classes: score 0 no coverage, score 1 coverage inferior or equal to 25 % of the spine head, score 2 coverage between 25 and 50 %, score 3 coverage above 50 %. Scale bar 0.5 µm. i Histogram of the mean perisynaptic ensheathement on neurons of different ages, as assessed by confocal microscopy [One-way ANOVA between groups, F(3,71) = 1.18, p = 0.32, n = 84–1,780 spines per group]

Mentions: We first assessed whether dendritic spines of adult-born neurons were ensheathed by astrocytic processes. Recently, a rabies virus (RABV)-based approach for mono-synaptic tracing of the inputs on adult-generated neurons unexpectedly resulted in the labeling of astrocytes (Deshpande et al. 2013; Vivar et al. 2012). To examine whether this RABV-mediated labeling of astrocytes resulted from a direct contact with new neurons, we transduced newborn neurons with a DsRed-encoding Moloney Murine Leukemia virus (MoMuLV; G-TVA retrovirus) co-expressing the EnvA receptor TVA (required for RABV internalization) and the RABV glycoprotein (G) required for subsequent synaptic transfer. Control injections were performed with a virus expressing DsRed and TVA, but not G. Five weeks later, mice were injected with an EnvA-pseudotyped RABV encoding for GFP and analyzed 1 week thereafter. On average 1.02 ± 0.21 RABV-labeled astrocytes were found per neuron in G-TVA retrovirally injected mice. This number is underestimated, since RABV-mediated trans-synaptic tracing does not label all presynaptic partners. In contrast, only 0.02 ± 0.02 labeled astrocytes were found in control virus-injected mice (p < 0.05, n = 3 mice, Student’s t test). Moreover, about 90 % of secondarily infected astrocytes had visible dendrites of RABV-infected new neurons crossing their territories (Fig. 1a), suggesting that astrocytes formed direct contacts with the dendrites of adult-born neurons.Fig. 1


Pre-existing astrocytes form functional perisynaptic processes on neurons generated in the adult hippocampus.

Krzisch M, Temprana SG, Mongiat LA, Armida J, Schmutz V, Virtanen MA, Kocher-Braissant J, Kraftsik R, Vutskits L, Conzelmann KK, Bergami M, Gage FH, Schinder AF, Toni N - Brain Struct Funct (2014)

Astrocytic perisynaptic processes ensheathe dendritic spines of adult-born neurons. aLeft RABV used for trans-synaptic tracing reveals astrocytes: Mice were infected with a MoMuLV expressing DsRed, protein G and TVA. Five weeks later, they were infected with RABV expressing GFP and examined 1 week later. Confocal micrograph maximal projection reveals GFP-labeled astrocytes (arrows) contacting a starter neuron (yellow) co-infected by MoMuLV and RABV. Presumable presynaptic neurons (RABV-only infected) are also labeled in green. Scale bar 20 µm. Right higher magnification single optical section micrograph showing the dendrite of a starter neuron (yellow) in close contact with GFP-labeled astrocytic processes. Scale bar 5 µm. b Three-dimensional reconstruction of a synapse between a dendritic spine (red) and an axon terminal (blue) ensheathed by an astrocytic perisynaptic process (green). Scale bar 0.25 µm. c Proportion of the different types of astrocytic ensheathement on spines of adult-born neuron synapses (left) and GFP-negative, control neurons (right). d Mean perisynaptic ensheathement on spines of different morphologies on adult-born neurons (Kruskal–Wallis test, p < 0.05, n = 50–100 spines per group). e Mean perisynaptic ensheathement on spines of different morphologies on control neurons (Kruskal–Wallis test, p < 0.05, n = 50–100 spines per group). F filopodia, T thin spines, M mushroom spines. f Electron micrographs of dendritic spines from newborn neurons (false-colored in red) and axon terminals (blue) ensheathed by an astrocytic perisynaptic process (green). From left to right: the perisynaptic process is found on the axon terminal only, on the dendritic spine only, on both synaptic partners or is absent. Scale bars 0.25 µm. gLeft panel confocal micrograph maximal projection of an adult-born neuron (red) in the dentate gyrus of an Aldh1l1-GFP mouse, 4 weeks post-injection. Scale bar 20 µm. Right panel confocal micrograph single optical section (after deconvolution) of a dendrite of a newborn neuron (red) in the dentate gyrus of an Aldh1l1-GFP mouse 4 weeks post-injection. Scale bar 2 µm. h. Confocal micrographs of dendritic spines with astrocytic processes scored in four classes: score 0 no coverage, score 1 coverage inferior or equal to 25 % of the spine head, score 2 coverage between 25 and 50 %, score 3 coverage above 50 %. Scale bar 0.5 µm. i Histogram of the mean perisynaptic ensheathement on neurons of different ages, as assessed by confocal microscopy [One-way ANOVA between groups, F(3,71) = 1.18, p = 0.32, n = 84–1,780 spines per group]
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Related In: Results  -  Collection

Show All Figures
getmorefigures.php?uid=PMC4481333&req=5

Fig1: Astrocytic perisynaptic processes ensheathe dendritic spines of adult-born neurons. aLeft RABV used for trans-synaptic tracing reveals astrocytes: Mice were infected with a MoMuLV expressing DsRed, protein G and TVA. Five weeks later, they were infected with RABV expressing GFP and examined 1 week later. Confocal micrograph maximal projection reveals GFP-labeled astrocytes (arrows) contacting a starter neuron (yellow) co-infected by MoMuLV and RABV. Presumable presynaptic neurons (RABV-only infected) are also labeled in green. Scale bar 20 µm. Right higher magnification single optical section micrograph showing the dendrite of a starter neuron (yellow) in close contact with GFP-labeled astrocytic processes. Scale bar 5 µm. b Three-dimensional reconstruction of a synapse between a dendritic spine (red) and an axon terminal (blue) ensheathed by an astrocytic perisynaptic process (green). Scale bar 0.25 µm. c Proportion of the different types of astrocytic ensheathement on spines of adult-born neuron synapses (left) and GFP-negative, control neurons (right). d Mean perisynaptic ensheathement on spines of different morphologies on adult-born neurons (Kruskal–Wallis test, p < 0.05, n = 50–100 spines per group). e Mean perisynaptic ensheathement on spines of different morphologies on control neurons (Kruskal–Wallis test, p < 0.05, n = 50–100 spines per group). F filopodia, T thin spines, M mushroom spines. f Electron micrographs of dendritic spines from newborn neurons (false-colored in red) and axon terminals (blue) ensheathed by an astrocytic perisynaptic process (green). From left to right: the perisynaptic process is found on the axon terminal only, on the dendritic spine only, on both synaptic partners or is absent. Scale bars 0.25 µm. gLeft panel confocal micrograph maximal projection of an adult-born neuron (red) in the dentate gyrus of an Aldh1l1-GFP mouse, 4 weeks post-injection. Scale bar 20 µm. Right panel confocal micrograph single optical section (after deconvolution) of a dendrite of a newborn neuron (red) in the dentate gyrus of an Aldh1l1-GFP mouse 4 weeks post-injection. Scale bar 2 µm. h. Confocal micrographs of dendritic spines with astrocytic processes scored in four classes: score 0 no coverage, score 1 coverage inferior or equal to 25 % of the spine head, score 2 coverage between 25 and 50 %, score 3 coverage above 50 %. Scale bar 0.5 µm. i Histogram of the mean perisynaptic ensheathement on neurons of different ages, as assessed by confocal microscopy [One-way ANOVA between groups, F(3,71) = 1.18, p = 0.32, n = 84–1,780 spines per group]
Mentions: We first assessed whether dendritic spines of adult-born neurons were ensheathed by astrocytic processes. Recently, a rabies virus (RABV)-based approach for mono-synaptic tracing of the inputs on adult-generated neurons unexpectedly resulted in the labeling of astrocytes (Deshpande et al. 2013; Vivar et al. 2012). To examine whether this RABV-mediated labeling of astrocytes resulted from a direct contact with new neurons, we transduced newborn neurons with a DsRed-encoding Moloney Murine Leukemia virus (MoMuLV; G-TVA retrovirus) co-expressing the EnvA receptor TVA (required for RABV internalization) and the RABV glycoprotein (G) required for subsequent synaptic transfer. Control injections were performed with a virus expressing DsRed and TVA, but not G. Five weeks later, mice were injected with an EnvA-pseudotyped RABV encoding for GFP and analyzed 1 week thereafter. On average 1.02 ± 0.21 RABV-labeled astrocytes were found per neuron in G-TVA retrovirally injected mice. This number is underestimated, since RABV-mediated trans-synaptic tracing does not label all presynaptic partners. In contrast, only 0.02 ± 0.02 labeled astrocytes were found in control virus-injected mice (p < 0.05, n = 3 mice, Student’s t test). Moreover, about 90 % of secondarily infected astrocytes had visible dendrites of RABV-infected new neurons crossing their territories (Fig. 1a), suggesting that astrocytes formed direct contacts with the dendrites of adult-born neurons.Fig. 1

Bottom Line: We found that the afferent and efferent synapses of newborn neurons are ensheathed by astrocytic processes, irrespective of the age of the neurons or the size of their synapses.Finally, some processes were found intercalated between newly formed dendritic spines and potential presynaptic partners, suggesting that they may also play a structural role in the connectivity of new spines.Together, these results indicate that pre-existing astrocytes remodel their processes to ensheathe synapses of adult-born neurons and participate to the functional and structural integration of these cells into the hippocampal network.

View Article: PubMed Central - PubMed

Affiliation: Department of Fundamental Neurosciences, University of Lausanne, 9 rue du Bugnon, 1005, Lausanne, Switzerland.

ABSTRACT
The adult dentate gyrus produces new neurons that morphologically and functionally integrate into the hippocampal network. In the adult brain, most excitatory synapses are ensheathed by astrocytic perisynaptic processes that regulate synaptic structure and function. However, these processes are formed during embryonic or early postnatal development and it is unknown whether astrocytes can also ensheathe synapses of neurons born during adulthood and, if so, whether they play a role in their synaptic transmission. Here, we used a combination of serial-section immuno-electron microscopy, confocal microscopy, and electrophysiology to examine the formation of perisynaptic processes on adult-born neurons. We found that the afferent and efferent synapses of newborn neurons are ensheathed by astrocytic processes, irrespective of the age of the neurons or the size of their synapses. The quantification of gliogenesis and the distribution of astrocytic processes on synapses formed by adult-born neurons suggest that the majority of these processes are recruited from pre-existing astrocytes. Furthermore, the inhibition of astrocytic glutamate re-uptake significantly reduced postsynaptic currents and increased paired-pulse facilitation in adult-born neurons, suggesting that perisynaptic processes modulate synaptic transmission on these cells. Finally, some processes were found intercalated between newly formed dendritic spines and potential presynaptic partners, suggesting that they may also play a structural role in the connectivity of new spines. Together, these results indicate that pre-existing astrocytes remodel their processes to ensheathe synapses of adult-born neurons and participate to the functional and structural integration of these cells into the hippocampal network.

No MeSH data available.


Related in: MedlinePlus