Dynamics of postsynaptic calcium involved in plasticity of visual cortex

在发育中的视皮层，重复刺激传入通路可引起皮层Layr II/III区突触传递的长时程增强(LTP)或长时程抑制(LTD)。然而，目前尚不清楚是什么因素决定了突触有效性的长期变化方向，即LT或LTD。目前的结果旨在解决这个问题。在视觉控制下，通过玻璃微管向Layr II/III神经元加载钙离子荧光指示剂Rhod 2，用于膜片钳记录。实验刺激Layr IV诱发兴奋性突触后电位(EPSP)，同时记录荧光强度的变化。强直刺激Layr IV诱导EPSPS的LTP，使树突状热点的荧光强度显著增加。另一方面，强直刺激导致EPSPS的荧光适度升高，导致LTD。综上所述，在突触输入过程中，突触后Ca~(2+)和Gt~(2+)的升高超过一定阈值即可诱发LTP，而弱或中度升高则可诱发LTP。

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.