Narasimhan K, Pessah I N, Linden D J
Department of Neuroscience, Johns Hopkins University School of Medicine, Baltimore, Maryland 21205, USA.
J Neurophysiol. 1998 Dec;80(6):2963-74. doi: 10.1152/jn.1998.80.6.2963.
Inositol-1,4,5-trisphosphate receptor-mediated Ca mobilization is not required for cerebellar long-term depression in reduced preparations. J. Neurophysiol. 80: 2963-2974, 1998. Cerebellar long-term depression (LTD) is a cellular model system of information storage in which coincident parallel fiber and climbing fiber activation of a Purkinje neuron (PN) gives rise to a sustained attenuation of parallel fiber-PN synaptic strength. Climbing fiber and parallel fiber inputs may be replaced by direct depolarization of the PN and exogenous glutamate pulses, respectively. The parallel fiber-PN synapse has a high-density of mGluR1 receptors that are coupled to phosphoinositide turnover. Several lines of evidence indicated that activation of mGluR1 by parallel fiber stimulation is necessary for the induction of cerebellar LTD. Because phosphoinositide hydrolysis has two initial products, 1, 2-diacylglycerol and inositol-1,4,5-trisphosphate (IP3), we wished to determine whether IP3 signaling via IP3 receptors and consequent Ca mobilization were necessary for the induction of cerebellar LTD. First, ratiometric imaging of free cytosolic Ca was performed on both acutely dissociated and cultured PNs. It was determined that the threshold for glutamate pulses to contribute to LTD induction was below the threshold for producing a Ca transient. Furthermore, the Ca transients produced by depolarization alone and glutamate plus depolarization were not significantly different. Second, the potent and selective IP3 receptor channel blocker xestospongin C was not found to affect the induction of LTD in either acutely dissociated or cultured PNs at a concentration that was sufficient to block mGluR1-evoked Ca mobilization. Third, replacement of mGluR activation by exogenous synthetic diacylglycerol in an LTD induction protocol was successful. Taken together, these results suggest that activation of an IP3 signaling cascade is not required for induction of cerebellar LTD in reduced preparations.
在简化制备中，小脑长时程抑制并不需要肌醇 - 1,4,5 - 三磷酸受体介导的钙动员。《神经生理学杂志》80: 2963 - 2974, 1998年。小脑长时程抑制（LTD）是一种信息存储的细胞模型系统，其中浦肯野神经元（PN）的平行纤维和攀缘纤维同时激活会导致平行纤维 - PN突触强度的持续减弱。攀缘纤维和平行纤维输入可分别被PN的直接去极化和外源性谷氨酸脉冲所替代。平行纤维 - PN突触具有高密度的与磷酸肌醇代谢偶联的代谢型谷氨酸受体1（mGluR1）。几条证据表明，平行纤维刺激激活mGluR1是诱导小脑LTD所必需的。由于磷酸肌醇水解有两个初始产物，1,2 - 二酰基甘油和肌醇 - 1,4,5 - 三磷酸（IP3），我们希望确定通过IP3受体的IP3信号传导以及随之而来的钙动员是否是诱导小脑LTD所必需的。首先，对急性分离和培养的PN进行了游离胞质钙的比率成像。已确定谷氨酸脉冲有助于LTD诱导的阈值低于产生钙瞬变的阈值。此外，单独去极化以及谷氨酸加去极化所产生的钙瞬变并无显著差异。其次，未发现强效且选择性的IP3受体通道阻滞剂海绵共栖菌素C在足以阻断mGluR1诱发的钙动员的浓度下影响急性分离或培养的PN中LTD的诱导。第三，在LTD诱导方案中用外源性合成二酰基甘油替代mGluR激活是成功的。综上所述，这些结果表明在简化制备中诱导小脑LTD不需要IP3信号级联的激活。
