Experimental early‐life febrile seizures cause a sustained increase in excitatory neurotransmission in newborn dentate granule cells

Prolonged febrile seizures (FS) are a risk factor for the development of hippocampal-associated temporal lobe epilepsy. The dentate gyrus is the major gateway to the hippocampal network and one of the sites in the brain where neurogenesis continues postnatally. Previously, we found that experimental FS increase the survival rate and structural integration of newborn dentate granule cells (DGCs). In addition, mature post-FS born DGCs express an altered receptor panel. Here, we aimed to study if these molecular and structural changes are accompanied by an altered cellular functioning. Experimental FS were induced by hyperthermia in 10-days-old Sprague-Dawley rats. Proliferating progenitor cells were labeled the next day by injecting green fluorescent protein expressing retroviral particles bilaterally in the dentate gyri. Eight weeks later, spontaneous excitatory and inhibitory postsynaptic events (sEPSCs and sIPSCs, respectively) were recorded from labeled DGCs using the whole-cell patch-clamp technique. Experimental FS resulted in a robust decrease of the inter event interval (p < .0001) and a small decrease of the amplitude of sEPSCs (p < .001). Collectively the spontaneous excitatory charge transfer increased (p < .01). Experimental FS also slightly increased the frequency of sIPSCs (p < .05), while the amplitude of these events decreased strongly (p < .0001). The net inhibitory charge transfer remained unchanged. Experimental, early-life FS have a long-term effect on post-FS born DGCs, as they display an increased spontaneous excitatory input when matured. It remains to be established if this presents a mechanism for FS-induced epileptogenesis.