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Determinants of functional coupling between astrocytes and respiratory neurons in the pre-Bötzinger complex.

Schnell C, Fresemann J, Hülsmann S - PLoS ONE (2011)

Bottom Line: In astrocytes that exhibited rhythmic potassium fluxes and glutamate transporter currents, we did not find a translation of respiratory neuronal activity into phase-locked astroglial calcium signals.We conclude that astrocytes do not exhibit respiratory-rhythmic calcium fluctuations when they are able to prevent synaptic glutamate accumulation.Calcium signaling is, however, observed when glutamate transport processes in astrocytes are suppressed or neuronal discharge activity is excessive.

View Article: PubMed Central - PubMed

Affiliation: Abt. Neuro- und Sinnesphysiologie, Zentrum Physiologie und Pathophysiologie, Georg-August-Universität, Göttingen, Germany.

ABSTRACT
Respiratory neuronal network activity is thought to require efficient functioning of astrocytes. Here, we analyzed neuron-astrocyte communication in the pre-Bötzinger Complex (preBötC) of rhythmic slice preparations from neonatal mice. In astrocytes that exhibited rhythmic potassium fluxes and glutamate transporter currents, we did not find a translation of respiratory neuronal activity into phase-locked astroglial calcium signals. In up to 20% of astrocytes, 2-photon calcium imaging revealed spontaneous calcium fluctuations, although with no correlation to neuronal activity. Calcium signals could be elicited in preBötC astrocytes by metabotropic glutamate receptor activation or after inhibition of glial glutamate uptake. In the latter case, astrocyte calcium elevation preceded a surge of respiratory neuron discharge activity followed by network failure. We conclude that astrocytes do not exhibit respiratory-rhythmic calcium fluctuations when they are able to prevent synaptic glutamate accumulation. Calcium signaling is, however, observed when glutamate transport processes in astrocytes are suppressed or neuronal discharge activity is excessive.

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Calcium signals in preBötC astrocytes evoked by activation of mGluR1-receptors.(A–C) Images show (A) the distribution of astrocytes identified by 900 nm 2-photon excitation and a CFP emission filter (BP 450–500 nm) and (B) Oregon Green BAPTA-1 AM staining (800 nm excitation and BP 511–551 nm emission filter). (C) Fluorescence traces from astrocyte somata shown in panel (A) in presence of DNQX and TTX. Application of quisqualate (5 µM) evoked a robust calcium elevation in 4 out of 5 astrocytes. (D–F) Astrocytic mGluR1-receptor expression is confirmed by immunohistochemistry. Panel (D) shows the confocal image of the EGFP-expressing astrocytes (green), and (E) the mGluR1-receptor expression. The arrows indicate astrocytes that express mGluR1 receptors (Cy-3, red). Note that neighboring neurons also show a high level of mGluR1-expression. In panel (F) the overlay of (D) and (E) is depicted.
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pone-0026309-g003: Calcium signals in preBötC astrocytes evoked by activation of mGluR1-receptors.(A–C) Images show (A) the distribution of astrocytes identified by 900 nm 2-photon excitation and a CFP emission filter (BP 450–500 nm) and (B) Oregon Green BAPTA-1 AM staining (800 nm excitation and BP 511–551 nm emission filter). (C) Fluorescence traces from astrocyte somata shown in panel (A) in presence of DNQX and TTX. Application of quisqualate (5 µM) evoked a robust calcium elevation in 4 out of 5 astrocytes. (D–F) Astrocytic mGluR1-receptor expression is confirmed by immunohistochemistry. Panel (D) shows the confocal image of the EGFP-expressing astrocytes (green), and (E) the mGluR1-receptor expression. The arrows indicate astrocytes that express mGluR1 receptors (Cy-3, red). Note that neighboring neurons also show a high level of mGluR1-expression. In panel (F) the overlay of (D) and (E) is depicted.

Mentions: In the present study, we tested whether group I metabotropic receptors contribute to glutamatergic Ca2+ signaling in preBötC astrocytes. Two-photon excitation microscopy revealed that the type I agonist quisqualate (5 µM) induced robust astrocyte calcium transients. We co-applied the AMPA/KA receptor blocker DNQX (25 µM) in these tests, since quisqualate has agonistic effects on AMPA receptors as well. In the presence of DNQX and 0.5 µM TTX, quisqualate induced calcium signals in 53±29% of EGFP-labeled preBötC astrocytes in 4 slices. As shown in figure 3, mGluR activation elicited short oscillatory calcium transients that rode on top of a much larger, longer lasting calcium elevation (figure 3C).


Determinants of functional coupling between astrocytes and respiratory neurons in the pre-Bötzinger complex.

Schnell C, Fresemann J, Hülsmann S - PLoS ONE (2011)

Calcium signals in preBötC astrocytes evoked by activation of mGluR1-receptors.(A–C) Images show (A) the distribution of astrocytes identified by 900 nm 2-photon excitation and a CFP emission filter (BP 450–500 nm) and (B) Oregon Green BAPTA-1 AM staining (800 nm excitation and BP 511–551 nm emission filter). (C) Fluorescence traces from astrocyte somata shown in panel (A) in presence of DNQX and TTX. Application of quisqualate (5 µM) evoked a robust calcium elevation in 4 out of 5 astrocytes. (D–F) Astrocytic mGluR1-receptor expression is confirmed by immunohistochemistry. Panel (D) shows the confocal image of the EGFP-expressing astrocytes (green), and (E) the mGluR1-receptor expression. The arrows indicate astrocytes that express mGluR1 receptors (Cy-3, red). Note that neighboring neurons also show a high level of mGluR1-expression. In panel (F) the overlay of (D) and (E) is depicted.
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Related In: Results  -  Collection

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getmorefigures.php?uid=PMC3198395&req=5

pone-0026309-g003: Calcium signals in preBötC astrocytes evoked by activation of mGluR1-receptors.(A–C) Images show (A) the distribution of astrocytes identified by 900 nm 2-photon excitation and a CFP emission filter (BP 450–500 nm) and (B) Oregon Green BAPTA-1 AM staining (800 nm excitation and BP 511–551 nm emission filter). (C) Fluorescence traces from astrocyte somata shown in panel (A) in presence of DNQX and TTX. Application of quisqualate (5 µM) evoked a robust calcium elevation in 4 out of 5 astrocytes. (D–F) Astrocytic mGluR1-receptor expression is confirmed by immunohistochemistry. Panel (D) shows the confocal image of the EGFP-expressing astrocytes (green), and (E) the mGluR1-receptor expression. The arrows indicate astrocytes that express mGluR1 receptors (Cy-3, red). Note that neighboring neurons also show a high level of mGluR1-expression. In panel (F) the overlay of (D) and (E) is depicted.
Mentions: In the present study, we tested whether group I metabotropic receptors contribute to glutamatergic Ca2+ signaling in preBötC astrocytes. Two-photon excitation microscopy revealed that the type I agonist quisqualate (5 µM) induced robust astrocyte calcium transients. We co-applied the AMPA/KA receptor blocker DNQX (25 µM) in these tests, since quisqualate has agonistic effects on AMPA receptors as well. In the presence of DNQX and 0.5 µM TTX, quisqualate induced calcium signals in 53±29% of EGFP-labeled preBötC astrocytes in 4 slices. As shown in figure 3, mGluR activation elicited short oscillatory calcium transients that rode on top of a much larger, longer lasting calcium elevation (figure 3C).

Bottom Line: In astrocytes that exhibited rhythmic potassium fluxes and glutamate transporter currents, we did not find a translation of respiratory neuronal activity into phase-locked astroglial calcium signals.We conclude that astrocytes do not exhibit respiratory-rhythmic calcium fluctuations when they are able to prevent synaptic glutamate accumulation.Calcium signaling is, however, observed when glutamate transport processes in astrocytes are suppressed or neuronal discharge activity is excessive.

View Article: PubMed Central - PubMed

Affiliation: Abt. Neuro- und Sinnesphysiologie, Zentrum Physiologie und Pathophysiologie, Georg-August-Universität, Göttingen, Germany.

ABSTRACT
Respiratory neuronal network activity is thought to require efficient functioning of astrocytes. Here, we analyzed neuron-astrocyte communication in the pre-Bötzinger Complex (preBötC) of rhythmic slice preparations from neonatal mice. In astrocytes that exhibited rhythmic potassium fluxes and glutamate transporter currents, we did not find a translation of respiratory neuronal activity into phase-locked astroglial calcium signals. In up to 20% of astrocytes, 2-photon calcium imaging revealed spontaneous calcium fluctuations, although with no correlation to neuronal activity. Calcium signals could be elicited in preBötC astrocytes by metabotropic glutamate receptor activation or after inhibition of glial glutamate uptake. In the latter case, astrocyte calcium elevation preceded a surge of respiratory neuron discharge activity followed by network failure. We conclude that astrocytes do not exhibit respiratory-rhythmic calcium fluctuations when they are able to prevent synaptic glutamate accumulation. Calcium signaling is, however, observed when glutamate transport processes in astrocytes are suppressed or neuronal discharge activity is excessive.

Show MeSH
Related in: MedlinePlus