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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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Analysis of respiratory-rhythmic astrocytic currents (Iresp,A).In panel (A) the effect of BaCl2 on Iresp,A is shown. Data, for each cell normalized (I/Imax) to the largest current measured over the range of holding potentials, are given for the different holding potentials from −90 mV to +20 mV. Error bars indicate mean ± SEM. The number of cells is indicated below each set of data points. Panel (B) shows cycle-averaged currents (holding potential −70 mV) that were recorded from the rhythmic astrocyte (C) under control conditions, in the presence of barium (BaCl2, 100 µM) and after additional inhibition of glutamate uptake by dihydrokainate (DHK, 300 µM). The cycle-averaged traces of the corresponding integrated preBötC field potential are depicted underneath.
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pone-0026309-g002: Analysis of respiratory-rhythmic astrocytic currents (Iresp,A).In panel (A) the effect of BaCl2 on Iresp,A is shown. Data, for each cell normalized (I/Imax) to the largest current measured over the range of holding potentials, are given for the different holding potentials from −90 mV to +20 mV. Error bars indicate mean ± SEM. The number of cells is indicated below each set of data points. Panel (B) shows cycle-averaged currents (holding potential −70 mV) that were recorded from the rhythmic astrocyte (C) under control conditions, in the presence of barium (BaCl2, 100 µM) and after additional inhibition of glutamate uptake by dihydrokainate (DHK, 300 µM). The cycle-averaged traces of the corresponding integrated preBötC field potential are depicted underneath.

Mentions: To test for periodic membrane current transients in astrocytes of the preBötC that coincide with rhythmic neuron discharges, we performed whole-cell voltage-clamp recordings from fluorescently labeled astrocytes in the slice preparation. We recorded from a total of 569 fluorescent astrocytes (Figure 1A). As typical, these astrocytes exhibited predominantly passive currents that were distinguished by a linear current-voltage relationship in whole-cell recordings (Figure 1D). Fifty-nine of these astrocytes (10.4%) also exhibited membrane current fluctuations (Iresp,A) that were in phase with the rhythmic discharges of preBötC neurons. Since Iresp,A current amplitude was imbedded to a large extent in background noise (figure 1B), it was not possible to measure current accurately from the raw data. Thus we used cycle triggered averaging to estimate the amplitude, which in 27 astrocytes was –5.9±0.7 pA (mean ± SEM) at Vhold = −70 mV (figure 1C). Iresp,A was recorded as an inward current at clamping potentials between −90 mV and +20 mV (see figure 2A).


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

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

Analysis of respiratory-rhythmic astrocytic currents (Iresp,A).In panel (A) the effect of BaCl2 on Iresp,A is shown. Data, for each cell normalized (I/Imax) to the largest current measured over the range of holding potentials, are given for the different holding potentials from −90 mV to +20 mV. Error bars indicate mean ± SEM. The number of cells is indicated below each set of data points. Panel (B) shows cycle-averaged currents (holding potential −70 mV) that were recorded from the rhythmic astrocyte (C) under control conditions, in the presence of barium (BaCl2, 100 µM) and after additional inhibition of glutamate uptake by dihydrokainate (DHK, 300 µM). The cycle-averaged traces of the corresponding integrated preBötC field potential are depicted underneath.
© Copyright Policy
Related In: Results  -  Collection

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

pone-0026309-g002: Analysis of respiratory-rhythmic astrocytic currents (Iresp,A).In panel (A) the effect of BaCl2 on Iresp,A is shown. Data, for each cell normalized (I/Imax) to the largest current measured over the range of holding potentials, are given for the different holding potentials from −90 mV to +20 mV. Error bars indicate mean ± SEM. The number of cells is indicated below each set of data points. Panel (B) shows cycle-averaged currents (holding potential −70 mV) that were recorded from the rhythmic astrocyte (C) under control conditions, in the presence of barium (BaCl2, 100 µM) and after additional inhibition of glutamate uptake by dihydrokainate (DHK, 300 µM). The cycle-averaged traces of the corresponding integrated preBötC field potential are depicted underneath.
Mentions: To test for periodic membrane current transients in astrocytes of the preBötC that coincide with rhythmic neuron discharges, we performed whole-cell voltage-clamp recordings from fluorescently labeled astrocytes in the slice preparation. We recorded from a total of 569 fluorescent astrocytes (Figure 1A). As typical, these astrocytes exhibited predominantly passive currents that were distinguished by a linear current-voltage relationship in whole-cell recordings (Figure 1D). Fifty-nine of these astrocytes (10.4%) also exhibited membrane current fluctuations (Iresp,A) that were in phase with the rhythmic discharges of preBötC neurons. Since Iresp,A current amplitude was imbedded to a large extent in background noise (figure 1B), it was not possible to measure current accurately from the raw data. Thus we used cycle triggered averaging to estimate the amplitude, which in 27 astrocytes was –5.9±0.7 pA (mean ± SEM) at Vhold = −70 mV (figure 1C). Iresp,A was recorded as an inward current at clamping potentials between −90 mV and +20 mV (see figure 2A).

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