Abstracts

Rationale: Thrombospondins are astrocyte-secreted proteins that promote developmental synaptogenesis in the central nervous system by binding to the alpha2-delta1 subunit of voltage-gated calcium channels. We hypothesize that overexpression of alpha2-delta1 receptors in transgenic (TG) mice, would result in increased excitatory connectivity, hyperexcitable cortical networks and seizures. Methods: To test this hypothesis, we used behavioral observations, whole cell patch clamp and extracellular field potential recordings from in vitro brain slices, and video/EEG monitoring of mice with chronically implanted epidural electrodes. In addition, we assessed the colocalization of Vglut1- and Vglut2-IR profiles with PSD95-IR in control and TG mice. Results: Epileptiform field potentials were evoked in layers II/III and V of brain slices from TG mice (n = 6 mice) but not control (n = 6 mice). Whole cell recordings from layer V pyramidal cells in somatosensory cortical slices showed increased frequency and amplitude of miniature (m) and spontaneous (s) EPSCs. Mean peak amplitude of sEPSCs was 32.6 ± 1.2 pA (n = 14 cells) in TG mice and 26.1 ± 1.5 pA in control (n = 11; unpaired t-test: P < 0.005). Mean frequency of sEPSCs was 6.5 ± 1.6Hz in TG mice and 2 ± 0.3Hz in control (unpaired t-test: P < 0.05). In addition, recurrent spontaneous polysynaptic "burst-like" discharges, were recorded in 10/14 layer V Pyr cells from TG mice vs. 1/11 Pyr cells from control (χ2 test; df = 1; χ2 = 9.71, P < 0.005). Dual immunoreactivity for Vglut2 and PSD95 showed an increased density of close appositions in TG mice compared to control, suggesting an increased number of excitatory synapses. Video-EEG monitoring of chronically implanted mice aged >