Adrenoceptors were among the first neurotransmitter receptors identified in glial cells, but it is not known whether these receptors meditate glial responses during neuronal activity. We show that repetitive nerve activity evoked a rise of intracellular calcium in Bergmann glia and neighboring Purkinje neurons of cerebellar slices of mice. The glial but not the neuronal calcium transient persisted during block of ionotropic and metabotropic glutamate receptors. In contrast, the glial calcium response was abolished by cyclopiazonic acid and prazosin; however, prazosin affected neither the inward current nor the resulting depolarization that accompanied the stimulus-induced glial calcium transients. The glial depolarization was attenuated by 38% by the mixture of glutamate receptor blockers, which abolished the evoked neuronal depolarization and afterhyperpolarization. Ba(2+) reduced the glial currents by 66% without affecting the concomitant calcium transients. In the presence of Ba(2+), the mixture of glutamate receptor blockers exerted no effect on the glial inward current or calcium rise. Furthermore, Ba(2+) greatly potentiated both the activity-related Purkinje cell inward current and the accompanying neuronal calcium rises. The results indicate that release of noradrenaline from afferent fibers activates a glial alpha(1) adrenoceptor that promotes calcium release from intracellular stores. Glial calcium rises are known to stimulate a diversity of processes such as transmitter release, energy metabolism, or proliferation. Thus the adrenoceptor-mediated mechanism described here is well suited for feedback modulation of neuronal function that is independent of glutamate.
In hippocampal slices from rats, dialysis with rhodamine-123 (Rh-123) and/or fura-2 via the patch electrode allowed monitoring of mitochondrial potential (DeltaPsi) changes and intracellular Ca(2+) ([Ca(2+)](i)) of CA1 pyramidal neurons. Plasmalemmal depolarization to 0 mV caused a mean [Ca(2+)](i) rise of 300 nM and increased Rh-123 fluorescence signal (RFS) by =50% of control. The evoked RFS, indicating depolarization of DeltaPsi, and the [Ca(2+)](i) transient were abolished by Ca(2+)-free superfusate or exposure of Ni(2+)/Cd(2+). Simultaneous measurements of RFS and [Ca(2+)](i) showed that the kinetics of both the Ca(2+) rise and recovery were considerably faster than those of the DeltaPsi depolarization. The plasmalemmal Ca(2+)/H(+) pump blocker eosin-B potentiated the peak of the depolarization-induced RFS and delayed recovery of both the RFS and [Ca(2+)](i) transient. Thus the DeltaPsi depolarization due to plasmalemmal depolarization is related to mitochondrial Ca(2+) sequestration secondary to Ca(2+) influx through voltage-gated Ca(2+) channels. CN(-) elevated [Ca(2+)](i) by <50 nM but increased RFS by 221% as a result of extensive depolarization of DeltaPsi. Oligomycin decreased RFS by 52% without affecting [Ca(2+)](i). In the presence of oligomycin, CN(-) and p-trifluoromethoxy-phenylhydrazone (FCCP) elevated [Ca(2+)](i) by <50 nM and increased RFS by 285 and 290%, respectively. Accordingly, the metabolism-related DeltaPsi changes are independent of [Ca(2+)](i). Imaging techniques revealed that evoked [Ca(2+)](i) rises are distributed uniformly over the soma and primary dendrites, whereas corresponding changes in RFS occur more localized in subregions within the soma. The results show that microfluorometric measurement of the relation between mitochondrial function and intracellular Ca(2+) is feasible in whole cell recorded mammalian neurons in situ.
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