Najlerahim A, Williams S F, Pearson R C, Jefferys J G
Department of Biomedical Science, University of Sheffield, UK.
Exp Brain Res. 1992;90(2):332-42. doi: 10.1007/BF00227246.
A few mouse minimum lethal doses (MLD) of tetanus toxin injected into rat hippocampus triggers prolonged changes in neuronal function. Spontaneously recurring epileptic discharges arise in both the injected and the contralateral, uninjected hippocampus. The seizures remit after about 6 weeks, to be succeeded by a permanent depression of hippocampal neuronal responses. There is no evidence of any loss of pyramidal cells at this low dose of toxin. Here we studied presumptive inhibitory, GABAergic neurons, using in situ hybridization (ISH) with a probe directed against the mRNA encoding glutamic acid decarboxylase (GAD), at each of 1, 2, 4 and 8 weeks after injection of tetanus toxin. Epileptic activity was recorded from hippocampal slices prepared from both injected and contralateral hippocampi of rats at each time point, unexpectedly persisting until 8 weeks. There were no significant differences in the numbers of neurons containing GAD mRNA between toxin- and vehicle-injected and control rats in any hippocampal subfield, at any survival time, except for an apparently transient loss of hilar signal in vehicle-injected rats at 1 and 2 weeks which we attribute to a significant, transient loss of neuronal GAD mRNA to below the threshold for detection by ISH using this probe. In contrast there was a marked increase in GAD mRNA in the toxin-injected group, which reached a peak at 4 weeks, and returned to control levels by 8 weeks. The changes were bilateral and were most marked in the hilus of the dentate area, but were also significant in CA3 and CA1. Upregulation of GAD mRNA was preceded by an increase in the levels of the mRNA for the alpha subunit of the GTP binding protein, Gs (Gs alpha), at 2 weeks which affected the GABAergic neurons selectively, and not the pyramidal or granule cells. These marked changes in GAD mRNA may contribute to putative adaptive responses within GABAergic neurons, which would help contain epileptic activity in these chronic foci. The changes in GAD expression may be due to mechanisms acting through an increase in mRNA encoding Gs alpha.
向大鼠海马体注射几小鼠最小致死剂量（MLD）的破伤风毒素会引发神经元功能的长期变化。在注射侧和对侧未注射的海马体中都会出现自发反复的癫痫放电。癫痫发作在约6周后缓解，随后海马体神经元反应出现永久性抑制。在这种低剂量毒素作用下，没有证据表明锥体细胞有任何损失。在此，我们在注射破伤风毒素后的第1、2、4和8周，使用针对编码谷氨酸脱羧酶（GAD）的mRNA的探针进行原位杂交（ISH），研究假定的抑制性GABA能神经元。在每个时间点，从注射侧和对侧海马体制备的海马体切片中记录癫痫活动，出乎意料的是，癫痫活动一直持续到8周。在任何存活时间，除了在1周和2周时注射赋形剂的大鼠中门区信号明显短暂缺失（我们将其归因于神经元GAD mRNA显著短暂减少至低于使用该探针的ISH检测阈值）外，在任何海马亚区，注射毒素、注射赋形剂的大鼠和对照大鼠中含有GAD mRNA的神经元数量均无显著差异。相比之下，注射毒素组中GAD mRNA有明显增加，在4周时达到峰值，并在8周时恢复到对照水平。这些变化是双侧性的，在齿状区门区最为明显，但在CA3和CA1区也很显著。在GAD mRNA上调之前，GTP结合蛋白Gs的α亚基（Gsα）的mRNA水平在2周时增加，这选择性地影响了GABA能神经元，而不是锥体细胞或颗粒细胞。GAD mRNA的这些显著变化可能有助于GABA能神经元内的假定适应性反应，这将有助于控制这些慢性病灶中的癫痫活动。GAD表达的变化可能是由于通过增加编码Gsα的mRNA起作用的机制所致。
