Gant John C, Thibault Oliver, Blalock Eric M, Yang Jun, Bachstetter Adam, Kotick James, Schauwecker Paula E, Hauser Kurt F, Smith George M, Mervis Ron, Li YanFang, Barnes Gregory N
Departments of Molecular and Biomedical Pharmacology, University of Kentucky College of Medicine, Lexington, KY, USA.
Epilepsia. 2009 Apr;50(4):629-45. doi: 10.1111/j.1528-1167.2008.01725.x. Epub 2008 Jul 24.
Clinically, perturbations in the semaphorin signaling system have been associated with autism and epilepsy. The semaphorins have been implicated in guidance, migration, differentiation, and synaptic plasticity of neurons. The semaphorin 3F (Sema3F) ligand and its receptor, neuropilin 2 (NPN2) are highly expressed within limbic areas. NPN2 signaling may intimately direct the apposition of presynaptic and postsynaptic locations, facilitating the development and maturity of hippocampal synaptic function. To further understand the role of NPN2 signaling in central nevous system (CNS) plasticity, structural and functional alterations were assessed in NPN2 deficient mice.
In NPN2 deficient mice, we measured seizure susceptibility after kainic acid or pentylenetetrazol, neuronal excitability and synaptic throughput in slice preparations, principal and interneuron cell counts with immunocytochemical protocols, synaptosomal protein levels with immunoblots, and dendritic morphology with Golgi-staining.
NPN2 deficient mice had shorter seizure latencies, increased vulnerability to seizure-related death, were more likely to develop spontaneous recurrent seizure activity after chemical challenge, and had an increased slope on input/output curves. Principal cell counts were unchanged, but GABA, parvalbumin, and neuropeptide Y interneuron cell counts were significantly reduced. Synaptosomal NPN2 protein levels and total number of GABAergic synapses were decreased in a gene dose-dependent fashion. CA1 pyramidal cells showed reduced dendritic length and complexity, as well as an increased number of dendritic spines.
These data suggest the novel hypothesis that the Sema 3F signaling system's role in appropriate placement of subsets of hippocampal interneurons has critical downstream consequences for hippocampal function, resulting in a more seizure susceptible phenotype.
在临床上，信号素信号系统的紊乱与自闭症和癫痫有关。信号素与神经元的导向、迁移、分化及突触可塑性有关。信号素3F（Sema3F）配体及其受体神经纤毛蛋白2（NPN2）在边缘区域高度表达。NPN2信号可能直接引导突触前和突触后位置的并置，促进海马突触功能的发育和成熟。为了进一步了解NPN2信号在中枢神经系统（CNS）可塑性中的作用，我们评估了NPN2基因敲除小鼠的结构和功能改变。
在NPN2基因敲除小鼠中，我们测量了给予红藻氨酸或戊四氮后的癫痫易感性、脑片制备中的神经元兴奋性和突触通量、采用免疫细胞化学方法计数主神经元和中间神经元的细胞数量、采用免疫印迹法检测突触体蛋白水平以及采用高尔基染色法观察树突形态。
NPN2基因敲除小鼠的癫痫发作潜伏期较短，对癫痫相关死亡的易感性增加，在化学刺激后更易出现自发性反复癫痫活动，并且输入/输出曲线的斜率增加。主神经元细胞数量未变，但GABA、小白蛋白和神经肽Y中间神经元的细胞数量显著减少。突触体NPN2蛋白水平和GABA能突触的总数呈基因剂量依赖性降低。CA1锥体细胞的树突长度和复杂性降低，树突棘数量增加。
这些数据提出了一个新的假说，即Sema 3F信号系统在海马中间神经元亚群的适当定位中的作用对海马功能具有关键的下游影响，导致更易癫痫发作的表型。
