Abstract：
Long-term depression (LTD) of synaptic transmission at parallel fiber (PF)-Purkinje cell (PC) synapses plays an important role in cerebellum-related motor coordination and learning. LTD is induced by the conjunction of PF stimulation and climbing fiber (CF) stimulation or somatic PC depolarization, while long-term potentiation (LTP) is induced by PF stimulation alone. Therefore, it is considered that different types of stimulation induce different types of synaptic plasticity. However, we found that a small number of conjunctive stimulations (PF + somatic depolarization of PC) induced LTP, but did not induce LTD of a small size. This LTP was not associated with changes in paired-pulse ratio, suggesting postsynaptic origin. Additionally this LTP was dependent on nitric oxide. This LTP was also induced by a smaller number of physiological conjunctive PF and CF stimuli. These results suggested that a larger number or longer period of conjunctive stimulation is required to induce LTD by overcoming LTP. Ca2+ transients at the PC dendritic region was measured by calcium imaging during LTD-inducing conjunctive stimulation. Peak amplitude of Ca2+ transients increased gradually during repetitive conjunctive stimulation. Instantaneous peak amplitude was not different between the early phase and late phase, but the average amplitude was larger in the later phase than in the early phase. These results show that LTD overcomes LTP, and increased Ca2+ integration or a number of stimulations is required for LTD induction.
摘要：
平行纤维（PF）-浦肯野细胞（PC）突触的突触传递的长期抑制（LTD）在小脑相关的运动协调和学习中起重要作用。LTD是由PF刺激和攀爬纤维(CF)刺激或体细胞PC去极化联合诱导的，而长时程增强（LTP）仅由PF刺激诱导。因此,认为不同类型的刺激诱导不同类型的突触可塑性。然而,我们发现少量的联合刺激（PF+PC的体细胞去极化）诱导LTP，但没有诱导LTD的小尺寸。此LTP与成对脉冲比的变化无关，提示突触后起源。此外,该LTP依赖于一氧化氮。这种LTP也是由较少量的生理联合PF和CF刺激诱导的。这些结果表明，通过克服LTP来诱导LTD需要更多数量或更长时间的联合刺激。在LTD诱导的结膜刺激期间通过钙成像测量PC树突区域的Ca2瞬变。在重复的结膜刺激过程中，Ca2瞬变的峰值振幅逐渐增加。早期阶段和晚期阶段的瞬时峰值幅度没有差异，但后期的平均振幅大于早期。这些结果表明，LTD克服了LTP，LTD诱导需要增加的Ca2+积分或许多刺激。
