Bojovic Ognjen, Panja Debabrata, Bittins Margarethe, Bramham Clive R, Tjølsen Arne
Department of Biomedicine, University of Bergen, Jonas Lies vei 91, 5009 Bergen, Norway.
PLoS One. 2015 Apr 10;10(4):e0123604. doi: 10.1371/journal.pone.0123604. eCollection 2015.
Long-term potentiation induced by conditioning electrical stimulation of afferent fibers is a widely studied form of synaptic plasticity in the brain and the spinal cord. In the spinal cord dorsal horn, long-term potentiation is induced by a series of high-frequency trains applied to primary afferent fibers. Conditioning stimulation (CS) of sciatic nerve primary afferent fibers also induces expression of immediate early gene proteins in the lumbar spinal cord. However, the time course of immediate early gene expression and the rostral-caudal distribution of expression in the spinal cord have not been systematically studied. Here, we examined the effects of sciatic nerve conditioning stimulation (10 stimulus trains, 0.5 ms stimuli, 7.2 mA, 100 Hz, train duration 2 s, 8 s intervals between trains) on cellular expression of immediate early genes, Arc, c-Fos and Zif268, in anesthetized rats. Immunohistochemical analysis was performed on sagittal sections obtained from Th13- L5 segments of the spinal cord at 1, 2, 3, 6 and 12 h post-CS. Strikingly, all immediate early genes exhibited a monophasic increase in expression with peak increases detected in dorsal horn neurons at 2 hours post-CS. Regional analysis showed peak increases at the location between the L3 and L4 spinal segments. Both Arc, c-Fos and Zif268 remained significantly elevated at 2 hours, followed by a sharp decrease in immediate early gene expression between 2 and 3 hours post-CS. Colocalization analysis performed at 2 hours post-CS showed that all c-Fos and Zif268 neurons were positive for Arc, while 30% and 43% of Arc positive neurons were positive for c-Fos and Zif268, respectively. The present study identifies the spinal cord level and time course of immediate early gene (IEGP) expression of relevance for analysis of IEGPs function in neuronal plasticity and nociception.
由传入纤维的条件性电刺激诱导的长时程增强是在脑和脊髓中广泛研究的一种突触可塑性形式。在脊髓背角，通过对初级传入纤维施加一系列高频串刺激可诱导长时程增强。对坐骨神经初级传入纤维的条件性刺激（CS）也可诱导腰段脊髓中即早基因蛋白的表达。然而，即早基因表达的时间进程以及在脊髓中表达的头-尾分布尚未得到系统研究。在此，我们研究了坐骨神经条件性刺激（10个刺激串，0.5毫秒刺激，7.2毫安，100赫兹，串持续时间2秒，串间间隔8秒）对麻醉大鼠脊髓中即早基因Arc、c-Fos和Zif268细胞表达的影响。在CS后1、2、3、6和12小时，对从脊髓Th13-L5节段获得的矢状切片进行免疫组织化学分析。令人惊讶的是，所有即早基因的表达均呈现单相增加，在CS后2小时在背角神经元中检测到峰值增加。区域分析显示在L3和L4脊髓节段之间的位置出现峰值增加。Arc、c-Fos和Zif268在2小时时仍显著升高，随后在CS后2至3小时即早基因表达急剧下降。在CS后2小时进行的共定位分析表明，所有c-Fos和Zif268神经元的Arc均呈阳性，而分别有30%和43%的Arc阳性神经元的c-Fos和Zif268呈阳性。本研究确定了即早基因（IEGP）表达的脊髓水平和时间进程，这对于分析IEGPs在神经元可塑性和伤害感受中的功能具有重要意义。
