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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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Inhibition of astrocytic glutamate transport elicits robust calcium signals in astrocytes.Panels (A–D) show an example of fluorometric calcium imaging during glutamate transport: Panel (A) identifies astrocytes, which were loaded with the calcium indicator Oregon Green BAPTA-1 AM (panel B). (C) A blockade of astrocyte glutamate transporters by TFB–TBOA (1 µM) elicited calcium signals in astrocytes (green traces) that were, as shown in (D), not phase-locked to preBötC neuronal activity (preBötC ∫). In the second example (E–G) the effects of glutamate transport inhibition are investigated after mGluR1-blockade. When the incubation of the mGluR1-antagonist CPCCOEt (200 µM) was started 10 min before the application of TFB-TBOA the astrocytic calcium signals were suppressed. (G) Original OGB-1 AM calcium traces are shown from one respiratory neuron (1) and three astrocytes (green traces). Panel (E) shows location of the corresponding EGFP-labeled astrocytes and panel (F) the distribution of the OGB-1-AM labeling.
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pone-0026309-g006: Inhibition of astrocytic glutamate transport elicits robust calcium signals in astrocytes.Panels (A–D) show an example of fluorometric calcium imaging during glutamate transport: Panel (A) identifies astrocytes, which were loaded with the calcium indicator Oregon Green BAPTA-1 AM (panel B). (C) A blockade of astrocyte glutamate transporters by TFB–TBOA (1 µM) elicited calcium signals in astrocytes (green traces) that were, as shown in (D), not phase-locked to preBötC neuronal activity (preBötC ∫). In the second example (E–G) the effects of glutamate transport inhibition are investigated after mGluR1-blockade. When the incubation of the mGluR1-antagonist CPCCOEt (200 µM) was started 10 min before the application of TFB-TBOA the astrocytic calcium signals were suppressed. (G) Original OGB-1 AM calcium traces are shown from one respiratory neuron (1) and three astrocytes (green traces). Panel (E) shows location of the corresponding EGFP-labeled astrocytes and panel (F) the distribution of the OGB-1-AM labeling.

Mentions: We analyzed effects of blocking astrocyte glutamate transporters on Ca2+ signaling in astrocytes and neuron discharge properties in preBötC slice preparations. Bath application of TFB-TBOA (1 µM), a potent blocker of both glial glutamate transporters [26], evoked calcium signals in 22 of 25 (88%) astrocytes (n = 5 slices, figure 6). Complex Ca2+ waveforms were detected and consisted of relatively short bursts superimposed on larger, prolonged and slow decaying waves (figure 6D). The signal complexes were similar in appearance to those produced by mGluR1 activation.


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

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

Inhibition of astrocytic glutamate transport elicits robust calcium signals in astrocytes.Panels (A–D) show an example of fluorometric calcium imaging during glutamate transport: Panel (A) identifies astrocytes, which were loaded with the calcium indicator Oregon Green BAPTA-1 AM (panel B). (C) A blockade of astrocyte glutamate transporters by TFB–TBOA (1 µM) elicited calcium signals in astrocytes (green traces) that were, as shown in (D), not phase-locked to preBötC neuronal activity (preBötC ∫). In the second example (E–G) the effects of glutamate transport inhibition are investigated after mGluR1-blockade. When the incubation of the mGluR1-antagonist CPCCOEt (200 µM) was started 10 min before the application of TFB-TBOA the astrocytic calcium signals were suppressed. (G) Original OGB-1 AM calcium traces are shown from one respiratory neuron (1) and three astrocytes (green traces). Panel (E) shows location of the corresponding EGFP-labeled astrocytes and panel (F) the distribution of the OGB-1-AM labeling.
© Copyright Policy
Related In: Results  -  Collection

Show All Figures
getmorefigures.php?uid=PMC3198395&req=5

pone-0026309-g006: Inhibition of astrocytic glutamate transport elicits robust calcium signals in astrocytes.Panels (A–D) show an example of fluorometric calcium imaging during glutamate transport: Panel (A) identifies astrocytes, which were loaded with the calcium indicator Oregon Green BAPTA-1 AM (panel B). (C) A blockade of astrocyte glutamate transporters by TFB–TBOA (1 µM) elicited calcium signals in astrocytes (green traces) that were, as shown in (D), not phase-locked to preBötC neuronal activity (preBötC ∫). In the second example (E–G) the effects of glutamate transport inhibition are investigated after mGluR1-blockade. When the incubation of the mGluR1-antagonist CPCCOEt (200 µM) was started 10 min before the application of TFB-TBOA the astrocytic calcium signals were suppressed. (G) Original OGB-1 AM calcium traces are shown from one respiratory neuron (1) and three astrocytes (green traces). Panel (E) shows location of the corresponding EGFP-labeled astrocytes and panel (F) the distribution of the OGB-1-AM labeling.
Mentions: We analyzed effects of blocking astrocyte glutamate transporters on Ca2+ signaling in astrocytes and neuron discharge properties in preBötC slice preparations. Bath application of TFB-TBOA (1 µM), a potent blocker of both glial glutamate transporters [26], evoked calcium signals in 22 of 25 (88%) astrocytes (n = 5 slices, figure 6). Complex Ca2+ waveforms were detected and consisted of relatively short bursts superimposed on larger, prolonged and slow decaying waves (figure 6D). The signal complexes were similar in appearance to those produced by mGluR1 activation.

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