Involvement of ryanodine receptors in neurotrophin-induced hippocampal synaptic plasticity and spatial memory formation

摘要

Ryanodine receptors (RyR) amplify activity-dependent calcium influx via calcium-induced calcium release. Calcium signals trigger post-synaptic pathways in hippocampal neurons that underlie synaptic plasticity, learning, and memory. Recent evidence supports a role of the RyR2 and RyR3 isoforms in these processes. Along with calcium signals, brain-derived neurotrophic factor (BDNF) is a key signaling molecule for hippocampal synaptic plasticity and spatial memory. Upon binding to specific TrkB receptors, BDNF initiates complex signaling pathways that modify synaptic structure and function. Here, we show that BDNF-induced remodeling of hippocampal dendritic spines required functional RyR. Additionally, incubation with BDNF enhanced the expression of RyR2, RyR3, and PKM£, an atypical protein kinase C isof orm with key roles in hippocampal memory consolidation. Consistent with their increased RyR protein content BDNF-treated neurons generated larger RyR-mediated calcium signals than controls. Selective inhibition of RyR-mediated calcium release with inhibitory ryanodine concentrations prevented the PKM£, RyR2, and RyR3 protein content enhancement induced by BDNF. Intrahippocampal injection of BDNF or training rats in a spatial memory task enhanced PKM£, RyR2, RyR3, and BDNF hippocampal protein content, while injection of ryanodine at concentrations that stimulate RyR-mediated calcium release improved spatial memory learning and enhanced memory consolidation. We propose that RyR-generated calcium signals are key features of the complex neu-ronal plasticity processes induced by BDNF, which include increased expression of RyR2, RyR3, and PKM£ and the spine remodeling required for spatial memory formation.