Abstract
Learning and memory require coordinated structural and functional plasticity at neuronal glutamatergic synapses located on dendritic spines. Here, we investigated how the endoplasmic reticulum (ER) controls postsynaptic Ca(2+) signaling and long-term potentiation of dendritic spine size, i.e., sLTP that accompanies functional strengthening of glutamatergic synaptic transmission. In most ER-containing (ER+) spines, high-frequency optical glutamate uncaging (HFGU) induced long-lasting sLTP that was accompanied by a persistent increase in spine ER content downstream of a signaling cascade engaged by N-methyl-D-aspartate receptors (NMDARs), L-type Ca(2+) channels (LTCCs), and Orai1 channels, the latter being activated by stromal interaction molecule 1 (STIM1) in response to ER Ca(2+) release. In contrast, HFGU stimulation of ER-lacking (ER-) spines expressed only transient sLTP and exhibited weaker Ca(2+) signals noticeably lacking Orai1 and ER contributions. Consistent with spine ER regulating structural metaplasticity, delivery of a second stimulus to ER- spines induced ER recruitment along with persistent sLTP, whereas ER+ spines showed no additional increases in size or ER content in response to sequential stimulation. Surprisingly, the physical interaction between STIM1 and Orai1 induced by ER Ca(2+) release, but not the resulting Ca(2+) entry through Orai1 channels, proved necessary for the persistent increases in both spine size and ER content required for expression of long-lasting late sLTP.