Abbasi Saad, Kumar Sanjay S
Department of Biomedical Sciences, College of Medicine and Program in Neuroscience, Florida State University, Tallahassee, Florida.
Department of Biomedical Sciences, College of Medicine and Program in Neuroscience, Florida State University, Tallahassee, Florida
J Neurophysiol. 2015 Nov;114(5):2854-66. doi: 10.1152/jn.00823.2015. Epub 2015 Sep 16.
Temporal lobe epilepsy (TLE) is the most common form of epilepsy in adults and is often refractory to antiepileptic medications. The medial entorhinal area (MEA) is affected in TLE but mechanisms underlying hyperexcitability of MEA neurons require further elucidation. Previous studies suggest that inputs from the presubiculum (PrS) contribute to MEA pathophysiology. We assessed electrophysiologically how PrS influences MEA excitability using the rat pilocarpine model of TLE. PrS-MEA connectivity was confirmed by electrically stimulating PrS afferents while recording from neurons within superficial layers of MEA. Assessment of alterations in PrS-mediated synaptic drive to MEA neurons was made following focal application of either glutamate or NBQX to the PrS in control and epileptic animals. Here, we report that monosynaptic inputs to MEA from PrS neurons are conserved in epileptic rats, and that PrS modulation of MEA excitability is layer-specific. PrS contributes more to synaptic inhibition of LII stellate cells than excitation. Under epileptic conditions, stellate cell inhibition is significantly reduced while excitatory synaptic drive is maintained at levels similar to control. PrS contributes to both synaptic excitation and inhibition of LIII pyramidal cells in control animals. Under epileptic conditions, overall excitatory synaptic drive to these neurons is enhanced while inhibitory synaptic drive is maintained at control levels. Additionally, neither glutamate nor NBQX applied focally to PrS now affected EPSC and IPSC frequency of LIII pyramidal neurons. These layer-specific changes in PrS-MEA interactions are unexpected and of significance in unraveling pathophysiological mechanisms underlying TLE.
颞叶癫痫(TLE)是成人中最常见的癫痫形式,且通常对抗癫痫药物难治。内侧内嗅区(MEA)在TLE中会受到影响,但MEA神经元兴奋性过高的潜在机制仍需进一步阐明。先前的研究表明,来自前下托(PrS)的输入促成了MEA的病理生理过程。我们使用TLE的大鼠匹鲁卡品模型,通过电生理学方法评估PrS如何影响MEA的兴奋性。通过电刺激PrS传入纤维并记录MEA浅层神经元的活动,证实了PrS-MEA的连接性。在对照动物和癫痫动物中,向PrS局部应用谷氨酸或NBQX后,评估PrS介导的对MEA神经元的突触驱动的变化。在此,我们报告,癫痫大鼠中PrS神经元对MEA的单突触输入是保守的,并且PrS对MEA兴奋性的调节具有层特异性。PrS对II层星状细胞的突触抑制作用比对其兴奋作用贡献更大。在癫痫状态下,星状细胞的抑制作用显著降低,而兴奋性突触驱动维持在与对照相似的水平。在对照动物中,PrS对III层锥体细胞的突触兴奋和抑制均有作用。在癫痫状态下,对这些神经元的总体兴奋性突触驱动增强,而抑制性突触驱动维持在对照水平。此外,现在向PrS局部应用谷氨酸或NBQX均不影响III层锥体细胞的兴奋性突触后电流(EPSC)和抑制性突触后电流(IPSC)频率。PrS-MEA相互作用的这些层特异性变化出乎意料,对于阐明TLE潜在的病理生理机制具有重要意义。