Abstracts

Rationale: Status epilepticus (SE) is any seizure lasting more than 5 minutes. It is a life-threatening emergency that can result in de novo development or worsening of epilepsy and behavioral and cognitive comorbidities. Focal neocortical (F)SE in mice results in neuronal loss, increases in functional excitatory synaptic connectivity and hyperexcitability in neocortical networks in vitro. Previous reports have shown that prolonged neocortical seizures can induce injury to downstream targets, such as thalamus, that might contribute to long-term consequences of FSE. We hypothesized that the intense cortical output during SE would induce chronic structural and functional changes in excitatory connectivity within downstream targets, such as ventral posterolateral nucleus (VPL), ventral posteromedial nucleus (VPM), and the thalamic nucleus reticularis (nRt). The enhanced excitatory connectivity would result in alterations in thalamocortical circuit function.

Methods: With epidural application of gabazine (150µM) and 4-AP (150µM), we induced FSE over the somatosensory cortex of anesthetized mice. FSE was identified with electrographic recordings and contralateral focal myoclonic activity and was allowed to persist for ~2h. Ten and 30 days later we obtained confocal images of medial nRt, VPL and VPM sections immunoreacted for pre- and postsynaptic markers of excitatory synapses. We measured colocalized pixel areas for VGLUT1-PSD95 and VGLUT2-PSD95 to identify excitatory synapses of cortical and thalamic origin accordingly. Counts of NeuN labeled neurons within nRT ROIs were obtained from non-overlapping 40µm confocal sections and analyzed. Whole cell voltage clamp recordings in nRT neurons were used to measure the spontaneous EPSC frequency. Statistical significance was tested with Wilcoxon test with a p< 0.05.