Roles of presynaptic calcium stores at hipporampal mossy fiber synapse

Ryanodine受体介导细胞内Ca^<2+>的释放，调节神经元和非神经元细胞的各种功能。为了研究ryanodine受体在突触前Ca^<2+>动力学活动依赖性调节中的作用，我们采用光学方法选择性监测海马苔藓纤维- ca3突触突触前末端Ca^<2+>浓度。荧光Ca^<2+>指示剂rhod- 2am局部注射到CA3区透明层轴突束苔藓纤维中，对苔藓纤维进行选择性标记。监测突触部位的荧光强度，以评估突触前末端Ca^<2+>水平。应用ryanodine受体黑剂TMB-8选择性抑制苔藓纤维高频刺激引起的突触前Ca^<2+>瞬态。我们还研究了咖啡因通过ryanodine受体诱导Ca^<2+>从胞内储存释放，对苔藓纤维- ca3突触突触传递的影响。咖啡因的应用导致epsp领域的强大增强，而这种突触增强伴随着成对脉冲促进的显着减少。这些结果表明，ryanodine受体存在于海马体苔藓纤维突触的突触前末端，细胞内储存的Ca^<2+>释放在该突触的突触前Ca^<2+>动力学和突触可塑性的调节中起关键作用。

Ryanodine receptors mediate Ca^<2+> release from intracellular stores and regulate various functions of neuronal and non-neuronal cells. To investigate the roles of ryanodine receptors in activity-dependent modulation of presynaptic Ca^<2+> dynamics, we adopted optical methods to selectively monitor Ca^<2+> concentrations in the presynaptic terminals of mossy fiber-CA3 synapse in the hippocampus. Fluorescent Ca^<2+> indicator rhod-2 AM was locally injected into the axon bundles mossy fibers at stratum lucidum of CA3 region, resulting in selective labeling of the mossy fibers. Fluorescence intencity at the synaptic sites was monitored to assess the Ca^<2+> levels in the presynaptic terminals. Application of ryanodine receptor blacker TMB-8 selectively suppressed the presynaptic Ca^<2+> transient evoked by high frequency stimulation of the mossy fibers. We also investigated the effect of caffeine, which induces Ca^<2+> release from intracellular store through ryanodine receptors, on the synaptic transmission at mossy fiber-CA3 synapse. Application of caffeine caused robust enhancement of the field EPSPs, and this synaptic enhancement was accompanied by a marked reduction of paired-pulse facilitation. These results suggested that ryanodine receptors are present in the presynaptic terminals of the hippocampal mossy fiber synapses, and Ca^<2+> release from the intracellular stores plays a pivotal role in regulation of presynaptic Ca^<2+> dynamics as well as synaptic plasticity at this synapse.