Reymann K G, Matthies H K, Frey U, Vorobyev V S, Matthies H
Brain Res Bull. 1986 Sep;17(3):291-6. doi: 10.1016/0361-9230(86)90234-0.
A transient increase in extracellular calcium concentration causes a long-lasting enhancement of radiatum fibers evoked excitatory postsynaptic potential and population spike responses of CA1 pyramidal neurons which resembles long-term potentiation (LTP). The duration of this potentiation is much longer than described previously and is probably limited by the survival of the preparation itself (greater than 8 hr). Therefore, Ca-induced LTP can be used for the investigation of a postulated late phase of LTP. Ca effects were activity-independent, since the subsequently evoked responses were facilitated even when the presynaptic fibers were not concurrently stimulated during or immediately after superfusion with the high Ca medium. In contrast, if too frequent testing of the synaptic input was done during the high Ca pulse, a short lasting depression instead of potentiation was observed. A lower extracellular magnesium concentration in the standard medium (1.3 instead of 2.0 mM MgSO4) prevents the potentiation of the EPSP at least for the first few hours. Presumably, both tetanus- and Ca-induced LTP share some common mechanisms, since an additional tetanization after Ca induction was not followed by an additional LTP. Compared to the potentiation following tetanization, the Ca-induced LTP was, however, not accompanied by a potentiation of the EPSP/spike ratio within the range of the population spike threshold intensity.
细胞外钙浓度的短暂升高会导致辐射层纤维诱发的CA1锥体神经元兴奋性突触后电位和群体峰电位反应出现持久增强，这类似于长时程增强（LTP）。这种增强的持续时间比之前描述的要长得多，可能受标本存活时间的限制（超过8小时）。因此，钙诱导的LTP可用于研究假定的LTP晚期阶段。钙效应不依赖于活动，因为即使在高钙溶液灌注期间或之后立即不同时刺激突触前纤维，随后诱发的反应也会得到促进。相反，如果在高钙脉冲期间对突触输入进行过于频繁的测试，则会观察到短暂的抑制而非增强。标准培养基中较低的细胞外镁浓度（1.3 mM MgSO4而非2.0 mM）至少在最初几个小时内可阻止EPSP的增强。推测破伤风诱导的LTP和钙诱导的LTP有一些共同机制，因为在钙诱导后额外进行强直刺激并不会导致额外的LTP。然而，与破伤风诱导后的增强相比，在群体峰电位阈值强度范围内，钙诱导的LTP并不伴随EPSP/峰电位比率的增强。
