Essential role of astrocytes in rapid activity-dependent restructuration of the axon initial segment

One key regulator of neuronal excitability is the axon initial segment (AIS), a highly specialized axonal region, enriched in ion channels, where action potentials are initiated. The AIS can undergo significant morphological changes to fine-tune neuronal excitability in response to external perturbations. Long considered solely a homeostatic mechanism operating over long timescales (hours to days) to adjust excitability, we show here that this phenomenon can also occur rapidly, within minutes, following a brief period of high activity in layer 5 pyramidal neurons of the visual cortex. Because astrocytes have been known to regulate neuronal excitability, we explored the effects of gliotransmitters on this process and identified the calcium-binding protein S100{beta} from astrocytes to be required for the rapid reorganization of the AIS. O_FIG O_LINKSMALLFIG WIDTH=169 HEIGHT=200 SRC="FIGDIR/small/667937v3_ufig1.gif" ALT="Figure 1"> View larger version (30K): org.highwire.dtl.DTLVardef@1765348org.highwire.dtl.DTLVardef@155bf98org.highwire.dtl.DTLVardef@95c300org.highwire.dtl.DTLVardef@356376_HPS_FORMAT_FIGEXP M_FIG Graphical abstract C_FIG