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GABAA receptor activity shapes the formation of inhibitory synapses between developing medium spiny neurons.

Arama J, Abitbol K, Goffin D, Fuchs C, Sihra TS, Thomson AM, Jovanovic JN - Front Cell Neurosci (2015)

Bottom Line: When activity of GABAARs was under chronic blockade between 4-7 DIV, the structural properties of these synapses remained unchanged.In contrast, chronic inhibition of GABAARs between 7-14 DIV led to reduction in size of α1- and α1/α2-postsynaptic clusters and a concomitant increase in number and size of α2-postsynaptic clusters.Thus, the main subtypes of GABAergic synapses formed by MSNs are regulated by GABAAR activity, but in opposite directions, and thus appear to be driven by different molecular mechanisms.

View Article: PubMed Central - PubMed

Affiliation: UCL School of Pharmacy, University College London London, UK.

ABSTRACT
Basal ganglia play an essential role in motor coordination and cognitive functions. The GABAergic medium spiny neurons (MSNs) account for ~95% of all the neurons in this brain region. Central to the normal functioning of MSNs is integration of synaptic activity arriving from the glutamatergic corticostriatal and thalamostriatal afferents, with synaptic inhibition mediated by local interneurons and MSN axon collaterals. In this study we have investigated how the specific types of GABAergic synapses between the MSNs develop over time, and how the activity of GABAA receptors (GABAARs) influences this development. Isolated embryonic (E17) MSNs form a homogenous population in vitro and display spontaneous synaptic activity and functional properties similar to their in vivo counterparts. In dual whole-cell recordings of synaptically connected pairs of MSNs, action potential (AP)-activated synaptic events were detected between 7 and 14 days in vitro (DIV), which coincided with the shift in GABAAR operation from depolarization to hyperpolarization, as detected indirectly by intracellular calcium imaging. In parallel, the predominant subtypes of inhibitory synapses, which innervate dendrites of MSNs and contain GABAAR α1 or α2 subunits, underwent distinct changes in the size of postsynaptic clusters, with α1 becoming smaller and α2 larger over time, while both the percentage and the size of mixed α1/α2-postsynaptic clusters were increased. When activity of GABAARs was under chronic blockade between 4-7 DIV, the structural properties of these synapses remained unchanged. In contrast, chronic inhibition of GABAARs between 7-14 DIV led to reduction in size of α1- and α1/α2-postsynaptic clusters and a concomitant increase in number and size of α2-postsynaptic clusters. Thus, the main subtypes of GABAergic synapses formed by MSNs are regulated by GABAAR activity, but in opposite directions, and thus appear to be driven by different molecular mechanisms.

No MeSH data available.


Related in: MedlinePlus

Developmental changes in GABAergic MSN synapses. (A,B) Immunolabeling of GABAA receptor α1- (i,ii,vii; pink), α2-(iii,iv,vii; green), α1/α2- (v,vi,vii; white) subunit-containing GABAA receptor clusters, and presynaptic GABAergic terminals (ii,iv,vi,vii; red) along the primary dendrites of 7 and 14 DIV MSNs, respectively. (i–vi) Scale bar = 5 μm. (vii) Scale bar = 10 μm. (C) Increase in the number of GABAergic terminals making connections with primary dendrites of MSNs from 7 to 14 DIV (n = 23 dendrites at 7 DIV, n = 18 dendrites at 14 DIV). (D–F) Changes in the number (left panel), percentage (middle panel) and size (right panel) of synaptic α1-, α2-, and α1/α2-clusters, respectively, along the primary dendrites of MSNs from 7 to 14 DIV. The box plots display the median and IQRs of indicated synaptic parameters measured along the first 20 μm of primary dendrites (n = 45 dendrites at 7 DIV, n = 48 dendrites at 14 DIV) of total of n = 16 neurons from two independent experiments. Statistical analysis was performed using Mann Whitney test, *p < 0.05.
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Figure 5: Developmental changes in GABAergic MSN synapses. (A,B) Immunolabeling of GABAA receptor α1- (i,ii,vii; pink), α2-(iii,iv,vii; green), α1/α2- (v,vi,vii; white) subunit-containing GABAA receptor clusters, and presynaptic GABAergic terminals (ii,iv,vi,vii; red) along the primary dendrites of 7 and 14 DIV MSNs, respectively. (i–vi) Scale bar = 5 μm. (vii) Scale bar = 10 μm. (C) Increase in the number of GABAergic terminals making connections with primary dendrites of MSNs from 7 to 14 DIV (n = 23 dendrites at 7 DIV, n = 18 dendrites at 14 DIV). (D–F) Changes in the number (left panel), percentage (middle panel) and size (right panel) of synaptic α1-, α2-, and α1/α2-clusters, respectively, along the primary dendrites of MSNs from 7 to 14 DIV. The box plots display the median and IQRs of indicated synaptic parameters measured along the first 20 μm of primary dendrites (n = 45 dendrites at 7 DIV, n = 48 dendrites at 14 DIV) of total of n = 16 neurons from two independent experiments. Statistical analysis was performed using Mann Whitney test, *p < 0.05.

Mentions: Between 7 and 14 DIV, synaptic connections formed between MSNs undergo prominent changes in their number and structural properties (Figures 5A,B). The total number of GAD-65-positive terminals innervating the proximal dendrites (the first 20 μm from the cell body) increased significantly from 7.1 ± 0.9 (mean ± s.e.m., n = 23 dendrites) at 7 DIV to 10.3 ± 1.2 (mean ± s.e.m., n = 18 dendrites) at 14 DIV (p < 0.05, Two sample t-test; Figure 5C). In parallel with changes in presynaptic inputs, the number of synaptic GABAA receptor clusters and the percentage of these clusters in the population of all GABAA receptor clusters (synaptic and extrasynaptic) also changed but in a subtype-specific manner.


GABAA receptor activity shapes the formation of inhibitory synapses between developing medium spiny neurons.

Arama J, Abitbol K, Goffin D, Fuchs C, Sihra TS, Thomson AM, Jovanovic JN - Front Cell Neurosci (2015)

Developmental changes in GABAergic MSN synapses. (A,B) Immunolabeling of GABAA receptor α1- (i,ii,vii; pink), α2-(iii,iv,vii; green), α1/α2- (v,vi,vii; white) subunit-containing GABAA receptor clusters, and presynaptic GABAergic terminals (ii,iv,vi,vii; red) along the primary dendrites of 7 and 14 DIV MSNs, respectively. (i–vi) Scale bar = 5 μm. (vii) Scale bar = 10 μm. (C) Increase in the number of GABAergic terminals making connections with primary dendrites of MSNs from 7 to 14 DIV (n = 23 dendrites at 7 DIV, n = 18 dendrites at 14 DIV). (D–F) Changes in the number (left panel), percentage (middle panel) and size (right panel) of synaptic α1-, α2-, and α1/α2-clusters, respectively, along the primary dendrites of MSNs from 7 to 14 DIV. The box plots display the median and IQRs of indicated synaptic parameters measured along the first 20 μm of primary dendrites (n = 45 dendrites at 7 DIV, n = 48 dendrites at 14 DIV) of total of n = 16 neurons from two independent experiments. Statistical analysis was performed using Mann Whitney test, *p < 0.05.
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Related In: Results  -  Collection

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Figure 5: Developmental changes in GABAergic MSN synapses. (A,B) Immunolabeling of GABAA receptor α1- (i,ii,vii; pink), α2-(iii,iv,vii; green), α1/α2- (v,vi,vii; white) subunit-containing GABAA receptor clusters, and presynaptic GABAergic terminals (ii,iv,vi,vii; red) along the primary dendrites of 7 and 14 DIV MSNs, respectively. (i–vi) Scale bar = 5 μm. (vii) Scale bar = 10 μm. (C) Increase in the number of GABAergic terminals making connections with primary dendrites of MSNs from 7 to 14 DIV (n = 23 dendrites at 7 DIV, n = 18 dendrites at 14 DIV). (D–F) Changes in the number (left panel), percentage (middle panel) and size (right panel) of synaptic α1-, α2-, and α1/α2-clusters, respectively, along the primary dendrites of MSNs from 7 to 14 DIV. The box plots display the median and IQRs of indicated synaptic parameters measured along the first 20 μm of primary dendrites (n = 45 dendrites at 7 DIV, n = 48 dendrites at 14 DIV) of total of n = 16 neurons from two independent experiments. Statistical analysis was performed using Mann Whitney test, *p < 0.05.
Mentions: Between 7 and 14 DIV, synaptic connections formed between MSNs undergo prominent changes in their number and structural properties (Figures 5A,B). The total number of GAD-65-positive terminals innervating the proximal dendrites (the first 20 μm from the cell body) increased significantly from 7.1 ± 0.9 (mean ± s.e.m., n = 23 dendrites) at 7 DIV to 10.3 ± 1.2 (mean ± s.e.m., n = 18 dendrites) at 14 DIV (p < 0.05, Two sample t-test; Figure 5C). In parallel with changes in presynaptic inputs, the number of synaptic GABAA receptor clusters and the percentage of these clusters in the population of all GABAA receptor clusters (synaptic and extrasynaptic) also changed but in a subtype-specific manner.

Bottom Line: When activity of GABAARs was under chronic blockade between 4-7 DIV, the structural properties of these synapses remained unchanged.In contrast, chronic inhibition of GABAARs between 7-14 DIV led to reduction in size of α1- and α1/α2-postsynaptic clusters and a concomitant increase in number and size of α2-postsynaptic clusters.Thus, the main subtypes of GABAergic synapses formed by MSNs are regulated by GABAAR activity, but in opposite directions, and thus appear to be driven by different molecular mechanisms.

View Article: PubMed Central - PubMed

Affiliation: UCL School of Pharmacy, University College London London, UK.

ABSTRACT
Basal ganglia play an essential role in motor coordination and cognitive functions. The GABAergic medium spiny neurons (MSNs) account for ~95% of all the neurons in this brain region. Central to the normal functioning of MSNs is integration of synaptic activity arriving from the glutamatergic corticostriatal and thalamostriatal afferents, with synaptic inhibition mediated by local interneurons and MSN axon collaterals. In this study we have investigated how the specific types of GABAergic synapses between the MSNs develop over time, and how the activity of GABAA receptors (GABAARs) influences this development. Isolated embryonic (E17) MSNs form a homogenous population in vitro and display spontaneous synaptic activity and functional properties similar to their in vivo counterparts. In dual whole-cell recordings of synaptically connected pairs of MSNs, action potential (AP)-activated synaptic events were detected between 7 and 14 days in vitro (DIV), which coincided with the shift in GABAAR operation from depolarization to hyperpolarization, as detected indirectly by intracellular calcium imaging. In parallel, the predominant subtypes of inhibitory synapses, which innervate dendrites of MSNs and contain GABAAR α1 or α2 subunits, underwent distinct changes in the size of postsynaptic clusters, with α1 becoming smaller and α2 larger over time, while both the percentage and the size of mixed α1/α2-postsynaptic clusters were increased. When activity of GABAARs was under chronic blockade between 4-7 DIV, the structural properties of these synapses remained unchanged. In contrast, chronic inhibition of GABAARs between 7-14 DIV led to reduction in size of α1- and α1/α2-postsynaptic clusters and a concomitant increase in number and size of α2-postsynaptic clusters. Thus, the main subtypes of GABAergic synapses formed by MSNs are regulated by GABAAR activity, but in opposite directions, and thus appear to be driven by different molecular mechanisms.

No MeSH data available.


Related in: MedlinePlus