Bendotti C, Baldessari S, Pende M, Southgate T, Guglielmetti F, Samanin R
Laboratory of Neuropharmacology, Istituto di Ricerche Farmacologiche Mario Negrl, Milano, Italy.
Eur J Neurosci. 1997 Jan;9(1):93-101. doi: 10.1111/j.1460-9568.1997.tb01357.x.
Kainic acid-induced seizures, in adult rats produce neurodegeneration in the hippocampus followed by sprouting of the mossy fibres in the inner molecular layer of the dentate gyrus and changes in GAP-43 expression in the granule cells. In the present study we observed that 4 days after kainic acid injection a dense plexus of silver-impregnated degenerating terminals detected by Gallyas's method and a decrease of GAP-43 immunostaining was observed in the inner molecular layer of the dentate gyrus indicating deafferentiation of this region. This was associated with the formation of an intense GAP-43 immunostained band in the supragranular layer. MK-801, a non-competitive inhibitor of the NMDA receptor, which partially inhibited the behavioural seizures induced by KA, also protected from the inner molecular layer deafferentation and markedly reduced the expression of GAP-43 mRNA in the granule cells and the intense GAP-43 immunostained band in the supragranular layer, suggesting a relationship among these events. Two months after kainic acid injection the intense supragranular GAP-43 positive band was no longer evident but the whole inner molecular layer appeared more labelled in association with the formation of the collateral sprouting of the mossy fibres in the inner molecular layer as detected by Timm's staining. These effects were also markedly reduced by the pretreatment with MK-801. Taken together, these experiments indicate for the first time a direct relationship between the increase of GAP-43 immunostaining in the inner molecular layer of the dentate gyrus and the collateral sprouting of mossy fibres in this district in response to kainic acid induced seizures. This further supports the hypothesis that the early induction of GAP-43 in granule cells may be one of the molecular mechanisms required for the synaptic reorganization of the mossy fibres.
成年大鼠中，海藻酸诱导的癫痫发作会导致海马体发生神经退行性变，随后齿状回内分子层的苔藓纤维会出现出芽现象，同时颗粒细胞中GAP - 43的表达也会发生变化。在本研究中，我们观察到，注射海藻酸4天后，用加利亚斯方法检测到齿状回内分子层中有密集的银浸染变性终末丛，且GAP - 43免疫染色减少，表明该区域发生了去传入神经支配。这与颗粒上层中形成强烈的GAP - 43免疫染色带有关。MK - 801是一种NMDA受体的非竞争性抑制剂，它部分抑制了KA诱导的行为性癫痫发作，还能防止内分子层去传入神经支配，并显著降低颗粒细胞中GAP - 43 mRNA的表达以及颗粒上层中强烈的GAP - 43免疫染色带，提示这些事件之间存在关联。注射海藻酸两个月后，颗粒上层强烈的GAP - 43阳性带不再明显，但整个内分子层的标记似乎更多，这与通过廷氏染色检测到的内分子层苔藓纤维侧支出芽的形成有关。MK - 801预处理也显著降低了这些效应。综上所述，这些实验首次表明齿状回内分子层中GAP - 43免疫染色的增加与该区域苔藓纤维侧支出芽之间存在直接关系，这是对海藻酸诱导的癫痫发作的反应。这进一步支持了颗粒细胞中GAP - 43的早期诱导可能是苔藓纤维突触重组所需的分子机制之一的假说。
