Participation of dysplastic neurons in the abnormal circuitry of focal epileptogenic lesions

Pedro Royero1, Anne Quatraccioni2, Barbara Robens2, Thomas Ulas3, Kristian Händler4, Joachim Schultze3, Susanne Schoch2, Albert Becker2, Heinz Beck1

1 IEECR, University of Bonn
2 Institute of Neuropathology, University of Bonn
3 LIMES, University of Bonn

Focal epileptogenic lesions are characterized by the presence of dysplastic neurons with abnormal dendritic morphology. We have used a novel model of cortical malformations where focal cortical knock-down (KD) of a gene that we found to be down-regulated in dysplastic neurons of human cortical malformations, Ste20-like kinase (SLK), is achieved using in-utero electroporation. By performing in-vitro recordings while stimulating the subcortical white matter, we found that the amplitude of evoked-inhibitory postsynaptic currents (IPSCs) was much lower in SLK-KD compared to controls. Next, we asked whether this inhibitory input impairment resides specifically in one of the canonical input pathways of cortical neurons. To this end, we expressed channelrhodopsin-2 (ChR2) in cortical excitatory neurons and in thalamic nuclei to measure light-evoked feed-back and feed-forward PSCs, respectively. Remarkably, we found feed-back inputs to be unaffected, while both feed-forward EPSCs and IPSCs were reduced in SLK-KD neurons, with the excitation-inhibition balance strongly shifted towards excitation. C-fos staining indicated that this inhibitory deficit may result in a higher basal activity of SLK-KD neurons in-vivo. Finally, we aimed to assess the specific connection between the E/I imbalance and the transcriptional landscape of dysplastic neurons, by performing patch-clamp RNA sequencing. Our analysis showed that dysplastic neurons differentially express sets of genes involved in neoplastic processes as well as in neurological diseases like epilepsy, Parkinson’s and Alzheimer’s disease, for which further validation analysis will be performed. As a whole, our data suggest a novel mechanism underlying hyperexcitability in focal epileptogenic lesions, where a deficit in feed-forward inhibitory motifs causes augmented sensory recruitment of a dysplastic neuron population