Dynamics of postsynaptic calcium involved in plasticity of visual cortex

在发育中的视皮层中，传入通路的重复刺激被报道可诱导皮层II/III层突触传递的长时程增强（LTP）或长时程抑制（LTD）。然而，目前还不清楚是什么因素决定了突触功效的长期变化方向，即，本研究的目的是解决这一问题。从年轻的大鼠（出生后20-26天）的视皮层薄片。在视觉控制下，通过玻璃微量移液器将荧光Ca^2+指示剂rhod 2加载到第II/III层的神经元上，进行膜片钳记录。同时记录荧光强度的变化与兴奋性突触后电位（EPSPs）诱发的测试刺激layr IV。破伤风刺激layr IV，诱导LTP的EPSPs导致大量的荧光强度增加在树突热点。另一方面，强直刺激诱导荧光适度上升导致LTD的EPSPs。总之，我们认为突触后Ca^<2+>在突触输入过程中升高超过一定阈值会诱发LTP，而低于阈值的微弱或适度升高则会诱发LTD。

In the developing visual cortex, repetitive stimulation of afferent pathways was reported to induce long-term potentiation (LTP) or long-term depression (LTD) of synaptic transmission in layr II/III of the cortex. It was not clearly known, however, what factors determine the direction of long-term changes in synaptic efficacy, i.e., LT or LTD.The present results were designed to address this question.Thin slices of the visual cortex were prepared from young rats (postnatal days 20-26). Under visual control, neurons in layr II/III were loaded with a fluorescent Ca^<2+> indicator, rhod 2, through glass micropipettes for patch-clamp recording. Changes in fluorescence intensity were recorded simultaneously with excitaory postsynaptic potentials (EPSPs) evoked by test stimulation of layr IV.Tetanic stimulation of layr IV which induced LTP of EPSPs led to a massive increase in fluorescence intensity at dendritic hot spots. On the other hand, tetanic stimulation which induced a moderate rise of fluorescence led to LTD of EPSPs. In sum, it is suggested that a rise of postsynaptic Ca^<2+> during synaptic inputs beyond a certain threshold induces LTP while a weak or moderate rise below the threshold induces LTD.