Berretta N, Rossokhin A V, Cherubini E, Astrelin A V, Voronin L L
Biophysics Sector, International School of Advanced Studies, Trieste, Italy.
Neuroscience. 1999;93(2):469-77. doi: 10.1016/s0306-4522(99)00167-0.
Minimal excitatory postsynaptic potentials were evoked in CA3 pyramidal neurons by activation of the mossy fibres in hippocampal slices from seven- to 16-day-old rats. Conditioning intracellular depolarizing pulses were delivered as 50- or 100-Hz bursts. A statistically significant depression and potentiation was induced in four and five of 13 cases, respectively. The initial state of the synapses influenced the effect: the amplitude changes correlated with the pretetanic paired-pulse facilitation ratio. Afferent (mossy fibre) tetanization produced a significant depression in four of six inputs, and no significant changes in two inputs. Quantal content decreased or increased following induction of the depression or potentiation, respectively, whereas no significant changes in quantal size were observed. Compatible with presynaptic maintenance mechanisms of both depression and potentiation, changes in the mean quantal content were associated with modifications in the paired-pulse facilitation ratios, coefficient of variation of response amplitudes and number of response failures. Cases were encountered when apparently "presynaptically silent" synapses were converted into functional synapses during potentiation or when effective synapses became "presynaptically silent" when depression was induced, suggesting respective changes in the probability of transmitter release. It is concluded that, in juvenile rats, it is possible to induce lasting potentiation at the mossy fibre-CA3 synapses by purely postsynaptic stimulation, while afferent tetanization is accompanied by long-lasting depression. The data support the existence not only of a presynaptically induced, but also a postsynaptically induced form of long-term potentiation in the mossy fibre-CA3 synapse. Despite a postsynaptic induction mechanism, maintenance of both potentiation and depression is likely to occur presynaptically.
在7至16日龄大鼠海马切片中，通过激活苔藓纤维在CA3锥体神经元中诱发最小兴奋性突触后电位。条件性细胞内去极化脉冲以50或100赫兹的爆发形式发放。在13例中有4例和5例分别诱导出具有统计学意义的抑制和增强。突触的初始状态影响了这种效应：幅度变化与强直刺激前的双脉冲易化比率相关。传入（苔藓纤维）强直刺激在六个输入中的四个产生了显著的抑制，在两个输入中没有显著变化。在诱导抑制或增强后，量子含量分别降低或增加，而量子大小没有观察到显著变化。与抑制和增强的突触前维持机制一致，平均量子含量的变化与双脉冲易化比率、反应幅度的变异系数和反应失败次数的改变有关。在增强过程中，明显“突触前沉默”的突触会转变为功能性突触，或者在诱导抑制时有效突触会变成“突触前沉默”，这表明递质释放概率发生了相应变化。结论是，在幼年大鼠中，通过纯粹的突触后刺激有可能在苔藓纤维 - CA3突触处诱导持久增强，而传入强直刺激则伴随着持久抑制。这些数据支持在苔藓纤维 - CA3突触中不仅存在突触前诱导的，而且存在突触后诱导的长期增强形式。尽管存在突触后诱导机制，但增强和抑制的维持可能都发生在突触前。
