Petrucci Alexandra N, Abel Ted, Wilcox Karen S
Department of Neuroscience and Pharmacology.
Iowa Neuroscience Institute, University of Iowa, Iowa City, IA, 52242, USA.
bioRxiv. 2025 May 21:2025.05.20.655185. doi: 10.1101/2025.05.20.655185.
Epilepsy affects one in twenty-six individuals. A major cause of epilepsy worldwide is viral encephalitis. Central nervous system infections can provoke seizures in the short term and increase the risk of spontaneous, recurrent seizures post-infection. However, the neural mechanisms underlying seizures during acute infection are unknown. These neuronal changes can be studied in C57BL6/J mice infected with Theiler's murine encephalomyelitis virus (TMEV). TMEV-infected mice experience seizures 3-8 days post-injection (DPI), clear the virus by DPI 14, and may develop chronic, acquired temporal lobe epilepsy. TMEV may incite seizures during the acute infection period through inflammation, reactive gliosis, and cell death in hippocampal area CA1. Here, we explore the neuronal circuits underlying acute seizures in TMEV-injected mice using c-Fos driven TRAP (targeted recombination in active populations). TRAP mice (c-Fos-CreERT2 x CAG-tdTomato) were injected with PBS or TMEV and gently handled on DPI 5 to induce seizures. 4-OHT was administered to mice either 1.5 or 3 hr after seizures to tag the active cells expressing c-Fos with tdTomato. After 1 week, the mice were sacrificed and whole mouse brains were sectioned and immunostained for tdTomato expression. Percent area of fluorescence was quantified, and comparisons were made between TMEV-injected mice and PBS controls, sites ipsilateral vs contralateral to TMEV injection site, and between sexes. TdTomato expression was elevated in the TMEV-injected mice in the ipsilateral and contralateral hippocampus, thalamus, lateral septal nucleus, basal ganglia, triangular septal nucleus, fornix, and corpus callosum. Critically, the expression pattern suggests that seizures induced on DPI 5 arise from the hilus, dentate gyrus, and CA3 hippocampal subregions. Generalized seizures during acute TMEV infection may have propagated to the contralateral hemisphere via CA3 and the hippocampal commissure. TRAP has not been previously utilized in the TMEV mouse model and these experiments address crucial questions regarding seizure spread during TMEV infection.
癫痫影响着每二十六人中的一人。在全球范围内，癫痫的一个主要病因是病毒性脑炎。中枢神经系统感染可在短期内引发癫痫发作，并增加感染后自发性、复发性癫痫发作的风险。然而，急性感染期间癫痫发作的神经机制尚不清楚。这些神经元变化可以在感染了泰勒氏鼠脑脊髓炎病毒（TMEV）的C57BL6/J小鼠中进行研究。感染TMEV的小鼠在注射后3至8天（DPI）会出现癫痫发作，在14 DPI时清除病毒，并可能发展为慢性获得性颞叶癫痫。TMEV可能在急性感染期通过海马CA1区的炎症、反应性胶质增生和细胞死亡引发癫痫发作。在此，我们使用c-Fos驱动的TRAP（活性群体中的靶向重组）来探索TMEV注射小鼠急性癫痫发作的神经回路。将TRAP小鼠（c-Fos-CreERT2×CAG-tdTomato）注射PBS或TMEV，并在DPI 5时轻轻处理以诱发癫痫发作。在癫痫发作后1.5或3小时给小鼠注射4-OHT，以用tdTomato标记表达c-Fos的活性细胞。1周后，处死小鼠，将整个小鼠脑切片并进行tdTomato表达的免疫染色。对荧光面积百分比进行量化，并在注射TMEV的小鼠与PBS对照组之间、TMEV注射部位同侧与对侧部位之间以及不同性别之间进行比较。在注射TMEV的小鼠同侧和对侧海马、丘脑、外侧隔核、基底神经节、三角隔核、穹窿和胼胝体中，tdTomato表达升高。至关重要的是，表达模式表明在DPI 5诱发的癫痫发作起源于海马的门区、齿状回和CA3亚区。急性TMEV感染期间的全身性癫痫发作可能通过CA3和海马连合扩散到对侧半球。TRAP此前尚未在TMEV小鼠模型中使用，这些实验解决了有关TMEV感染期间癫痫发作传播的关键问题。
