Ca2+ signaling in astrocytes is considered to be mainly mediated by metabotropic receptors linked to intracellular Ca2+ release. However, recent studies demonstrate a significant contribution of Ca2+ influx to spontaneous and evoked Ca2+ signaling in astrocytes, suggesting that Ca2+ influx might account for astrocytic Ca2+ signaling to a greater extent than previously thought. Here, we investigated AMPA-evoked Ca2+ influx into olfactory bulb astrocytes in mouse brain slices using Fluo-4 and GCaMP6s, respectively. Bath application of AMPA evoked Ca2+ transients in periglomerular astrocytes that persisted after neuronal transmitter release was inhibited by tetrodotoxin and bafilomycin A1. Withdrawal of external Ca2+ suppressed AMPA-evoked Ca2+ transients, whereas depletion of Ca2+ stores had no effect. Both Ca2+ transients and inward currents induced by AMPA receptor activation were partly reduced by Naspm, a blocker of Ca2+-permeable AMPA receptors lacking the GluA2 subunit. Antibody staining revealed a strong expression of GluA1 and GluA4 and a weak expression of GluA2 in periglomerular astrocytes. Our results indicate that Naspm-sensitive, Ca2+-permeable AMPA receptors contribute to Ca2+ signaling in periglomerular astrocytes in the olfactory bulb.

Astrocytes have a high impact on the structure of the central nervous system, as they control neural activity, development, and plasticity. Heterogeneity of astrocytes has been shown before, but so far only a few studies have demonstrated heterogeneous morphology of astrocytes concerning aging. In this study, we examined morphologic differences of astrocyte subpopulations in adult mice and the progression of these differences with age. We surveyed astrocytes in olfactory bulb slices of mice aged 3 months, 1 year and 2 years (three animals each age group), based on their appearance in anti-GFAP immunostaining. Based on this data we established three different types of astrocytes: type I (stellate), type II (elliptic), and type III (squid-like). We found that with the advanced age of the mice, astrocytes grow in size and complexity. Major changes occurred between the ages of 3 months and 1 year, while between 1 and 2 years no significant development in cell size and complexity could be detected. Our results show that astrocytes in the olfactory bulb are heterogeneous and undergo morphological transformation until late adolescence but not upon senescence. Structural plasticity is further substantiated by the expression of vimentin in some astrocyte processes in all age groups.