Abstracts

Rationale: Neonatal seizures are known to cause epilepsy and are associated with long-term cognitive and behavioral deficits including autism. Early-life seizures are found to reduce the number of silent synapses and cause deficits in long-term potentiation of CA1 hippocampal neurons (Zhou et al., J. Neurosci., 2011), resulting in alterations of excitatory-inhibitory (E-I) balance, and pathways involved in synaptic plasticity and learning. At birth, the inhibitory GABA circuit is initially underdeveloped and E-I balance is eventually reached with the appearance and maturation of inhibitory parvalbumin (PV) interneurons. Perineuronal nets (PNN) form around mature PV cells, and these mature, PNN-associated PV cells represent an attenuation of plasticity associated with immature PV (Hensch, Nat. Rev. Neurosci., 2005). Here we examine whether pentylenetetrazol (PTZ)-induced neonatal seizures disrupt E-I balance during postnatal development by altering the maturational profile of PV cells in the primary auditory cortex (A1).Methods: We induced acute seizures in male C57BL/6 mice by daily intraperitoneal injections of PTZ (60mg/kg) from P9-P11. Saline-injected littermates were used as controls. Mice were sacrified at P20 and P40, and and 16μm sections were collected. Immunohistochemistry was performed on sections containing A1 using antibodies for PV, Wisteria floribunda lectin (for PNN), and NeuN. Images were acquired using a Leica SP5 confocal microscope and the number of PV positive cells without PNN (PV+ only), PV cells with PNN (PV PNN+), or total PV+ cells in layer 4 of A1 per 100μm2 were calculated.Results: Preliminary data show no difference in the number of PV PNN+ cells, indicative of mature cells, at either age post-seizure. However, we found an increasing trend in PV+ only cells, indicative of immature cells, in P40 PTZ mice compared to controls (control: 0.183±0.034, n=12 fields from 4 mice; PTZ: 0.340±0.084, n=13 fields from 4 mice; p=0.0552 by Student’s t-test). Therefore we hypothesized that early-life seizures delay maturation of PV cells in A1. To test this, we examined the development change from P20 to P40 in post-seizure mice vs. controls. Because PNN plateaus between P21 and P40 in normal development (Bruckner et al., J. Comp. Neurol., 2000), we confirmed that there was no change in PV PNN+ cells in controls. Conversely, we observed a significant increase in PV PNN+ cells during the development of mice that had PTZ seizures (P20 PTZ: 0.790±0.092, n=15 fields from 4 mice; P40 PTZ: 1.059±0.128; p=0.025), representing a shift or delay in PV maturation due to early-life seizures. We are currently investigating earlier time points to evaluate whether this delay represents a compensation for an early decrease in PV cells.Conclusions: Our data show a delay in the maturation of parvalbumin cells, as manifested by an increase in PV neurons without perineuronal nets in the auditory cortex during development following PTZ-induced seizures. This suggests that early-life seizures can alter local inhibitory networks, which may affect plasticity in areas related to language acquisition.