Abstracts

Rationale: Early-life seizures are associated with cognitive and psychiatric impairments later in life. Since animals subjected to early-life Status Epilepticus (SE) do not show the neuropathological features classically associated with temporal lobe epilepsy, the neural mechanisms for these deficits are not known. Our hypothesis is that these behavioral dysfunctions could emerge from mild connectivity alterations between hippocampal CA1 and prefrontal cortex (PFC) since they are pathologically involved in psychiatric comorbidities of adult limbic epilepsy. Our aim was to investigate how early-life SE affects synaptic plasticity and the oscillatory activity of the CA1-PFC pathway, and how these effects relate to behavioral abnormalities. Methods: We induced a 2 h SE by means of lithium-pilocarpine in P12 male Wistar rats. Once adults, they were tested for spatial working memory (radial arm maze), exploratory behavior (open field), and sensorimotor gating (pre-pulse inhibition of the acoustic startle, PPI). They were submitted to an acute electrophysiological session, with PFC field responses being recorded upon electrical pulses (200 μs, 0.05 Hz, 150-300 μA) into CA1, both before (30 min) and after (240 min) CA1 high-frequency stimulation (HFS, 2 series of 10 trains, each train with 50 pulses at 250 Hz). In a second experiment, SE and control (Ctrl) animals were chronically implanted with microwire bundles in the PFC and CA1 for extracellular recordings (1000x gain, 0.03-3 kHz band pass and digitized at 10 kHz) during free behavior for 48 h. Stages of wake/sleep cycle were classified as slow wave sleep (SWS), rapid eye movement (REM) sleep, active wake and quiet wake using a machine learning algorithm. The protocol was approved by the Ethical Committee on Animal Research (159/2014).  Results: SE rats showed impaired radial arm maze performance (Student t-test, t(23)=-2141, p<0.05, n=11/14), hyperlocomotion (Student t-test, t(23)=-2,886, p<0.05, n=11/14), PPI deficit (Student t-test, t(23)=3,693, p<0.05, n=11/14), and a stronger long-term potentiation (two-way repeated measures ANOVA, F(1,12)=19,687; p<0,001, n=7/7). In the chronic recording session SE animals do not present differences in time spent in each stage of sleep cycle. However, SE rats showed a reduction in delta (1-4 Hz, Student t-test, t(14)=3.59, p<0.05, n=7/9) and an increase in theta frequencies power (5-10 Hz) during SWS (Student t-test, t(14)=-2.43, p<0.05, n=7/9) and a disruption in hippocampus cross-frequency coupling during SWS (Student t-test, t(14)=1.72, p<0.05, n=7/9) and REM (Student t-test, t(14)=1.66, p<0.05, n=7/9), between slow frequencies and high-gamma frequencies (65-100 Hz). No changes in neuronal density were detected with NeuN immunohistochemistry.  Conclusions: Our results indicate that typical behavioral abnormalities after early-life SE can occur independently of neuronal loss and are related to long-lasting CA1-PFC alterations. These data suggest possible functional impairments that can underlie psychiatry comorbidities in limbic epilepsy.  Funding: FAPESP: 2018/02303-4, 2016/17882-4