Glutamatergic and purinergic receptor-mediated calcium transients in Bergmann glial cells - PubMed (original) (raw)

Comparative Study

Glutamatergic and purinergic receptor-mediated calcium transients in Bergmann glial cells

Richard Piet et al. J Neurosci. 2007.

Abstract

Astrocytes respond to neuronal activity with [Ca2+]i increases after activation of specific receptors. Bergmann glial cells (BGs), astrocytes of the cerebellar molecular layer (ML), express various receptors that can mobilize internal Ca2+. BGs also express Ca2+ permeable AMPA receptors that may be important for maintaining the extensive coverage of Purkinje cell (PC) excitatory synapses by BG processes. Here, we examined Ca2+ signals in single BGs evoked by synaptic activity in cerebellar slices. Short bursts of high-frequency stimulation of the ML elicited Ca2+ transients composed of a small-amplitude fast rising phase, followed by a larger and slower rising phase. The first phase resulted from Ca2+ influx through AMPA receptors, whereas the second phase required release of Ca2+ from internal stores initiated by P2 purinergic receptor activation. We found that such Ca2+ responses could be evoked by direct activation of neurons releasing ATP onto BGs or after activation of metabotropic glutamate receptor 1 on these neurons. Moreover, examination of BG and PC responses to various synaptic stimulation protocols suggested that ML interneurons are likely the cellular source of ATP.

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Figures

Figure 1.

Figure 1.

ML stimulation evokes [Ca2+]i elevations in BG. A, Whole-cell current (Aa) and simultaneous Ca2+ transients (Ab) evoked in a BG by local ML stimulation (arrowhead). Inset, Magnification of the first phase of the Ca2+ transient. Ba, Bath application of 20 μ

m

NBQX inhibited the current and the first phase of the Ca2+ transient evoked in a BG by local ML stimulation. Control (gray) and NBQX traces were superimposed on the right to highlight the block of the first phase by NBQX. Bb, Histogram of the effect of NBQX on currents (I) and Ca2+ transients in 10 different BGs. **p < 0.01.

Figure 2.

Figure 2.

Ca2+ transient second phase involves Ca2+ release from internal stores and P2 receptor activation. Aa, Depleting internal Ca2+ stores with 20 μ

m

CPA inhibited the second phase of the BG Ca2+ transients but did not affect the first phase or the whole-cell current. Ab, Histogram of the effect of CPA (n = 6). Ba, PPADS (200 μ

m

) blocked the Ca2+ transient recorded in the presence of NBQX. Bb, Ca2+ transients evoked by pressure application of 1 m

m

ATP (open arrowhead) and their blockade by 200 μ

m

PPADS. Bc, Histogram of the effect of 20 μ

m

(n = 9) and 200 μ

m

PPADS (n = 4) on Ca2+ transients (Ca2+) and currents (I) evoked in BGs in the presence of NBQX and of 200 μ

m

PPADS on Ca2+ transients elicited by pressure application of ATP (Ca2+ ATP; n = 4). **p < 0.01.

Figure 3.

Figure 3.

Role of mGluR1 in the generation of BG Ca2+ transients. A, CPCCOet did not affect BG currents or Ca2+ transients evoked by local ML stimulation. B, TBOA enhanced the BG Ca2+ transient. The enhancement was blocked by CPCCOet. C, Histogram summarizing the effect of CPCCOet alone (n = 5), TBOA alone, and CPCCOet in the presence of TBOA (n = 6) on BG currents (I) and Ca2+ transients. *p < 0.05.

Figure 4.

Figure 4.

Distal PF stimulation evokes mGluR1-mediated Ca2+ transients in BGs. Aa, CPCCOet inhibits the second phase of BG Ca2+ transient evoked by distal stimulation of PFs without affecting the current (I). Ab, Histogram of the effects of CPCCOet (n = 5) and 200 μ

m

PPADS (n = 5) on BG currents and Ca2+ transients evoked in the same conditions. Ba, Coapplication of CPCCOet and PPADS did not inhibit BG Ca2+ transients evoked by distal PF stimulation more than CPCCOet alone. Bb, Histogram of the effect of CPCCOet and of CPCCOet plus PPADS in six cells. Ca, The effect of TBOA and TBOA plus PPADS on BG Ca2+ transients evoked by local ML stimulation. Cb, Histogram summarizing results of the experiment shown in Ca. **p < 0.01.

Figure 5.

Figure 5.

Neither BGs nor PCs are likely sources for ATP release. A, TTX blocked BG Ca2+ transients and whole-cell currents evoked by local ML stimulation. Histogram of the effect of TTX on the Ca2+ transient first and second phases and on whole-cell currents (I; n = 5). B, Neither single CF stimulations (left) nor short CF trains (right) evoked Ca2+ signals in BGs (top traces), but both elicited whole-cell currents (bottom traces). Insets show Ca2+ transients evoked in the corresponding cells when the stimulating electrode was moved to the ML. **p < 0.01.

Figure 6.

Figure 6.

Disynaptic GABA release via activation of mGluR1 on ML interneurons. A, Disynaptic IPSC evoked in a PC by distal PF stimulation (10 at 100 Hz; arrowhead) in NBQX and R-CPP. B–D, The effects of gabazine (B; n = 5), CPCCOet (C; n = 6), and PPADS (D; n = 5) on the disynaptic IPSC. E, Histogram summary. *p < 0.05, **p < 0.01.

Comment in

References

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