Ca(2+)-independent spine dynamics in cultured hippocampal neurons

Developing spines are highly dynamic processes that undergo rapid morphologic changes. We have investigated whether basal developmentally regulated spine motility is triggered by spontaneous changes in intracellular Ca(2+) ([Ca(2+)](i)). To address the link between Ca(2+) transients and motility, we have used the cell-permeable chelator BAPTA-AM. Consistent with others, we found that young cultured hippocampal neurons [7-13 days in vitro (DIV)] display significantly more spine motility than older neurons (14-21 days in vitro). Control experiments indicate that BAPTA-AM can lower basal [Ca(2+)](i) as well as block synaptically mediated Ca(2+) transients. However, globally buffering [Ca(2+)](i) by BAPTA-AM treatment failed to significantly alter the basal motility of developing spines measured at either relatively slow (5 min) or faster sampling times (every 20 s). We conclude that the basal spine motility of cultured hippocampal neurons may represent an intrinsic feature of developing neurons and is not necessarily choreographed by ongoing changes in [Ca(2+)](i) levels.