Abstracts

Rationale: Sleep deprivation is a common trigger for seizures among patients with epilepsy, but can also induce new-onset seizures. However, the physiological substrate(s) for these observations is(are) unknown. Here, we tested the effects of several sleep disruption paradigms on susceptibility to flurothyl-induced seizures and their resultant effects on hippocampal neuronal excitability.Methods: We used both acute and chronic sleep disruption (CSD) protocols in normal C57Bl/6 mice to mirror human conditions; CSD was broken down into either chronically restricted sleep (CSR) or chronically fragmented sleep (CSF; as in sleep apnea). Mice were placed in a 6 diameter cage with a flexible, rotating lever at the base; each rotation provided a tactile stimulus, forcing movement. With acute sleep disruption (ASD), the lever was programmed to rotate for 10 sec every minute for 24 hours, starting at P37 1. CSD was conducted using two protocols for 2 weeks each starting at P24 1: chronic sleep restriction (CSR; 10 sec/30 sec for the first 4 light hrs) and chronic sleep fragmentation (CSF; 10 sec/60 sec for the entire light period). Following sleep disruption experiments (that ended at P38 1), seizure susceptibility was assessed with the volatile convulsant flurothyl (bis[2,2,2-trifluroethyl] ether), which was infused at a rate of 20 l/min after mice were placed in a plexiglass chamber (7 x9 x11 ). Latencies to the first myoclonic jerk (MJ) and to generalized tonic-clonic (GTC) seizure activity were measured (after which animals were promptly removed from the chamber). To evaluate cellular excitability, separate groups of control and sleep disrupted mice were used for whole-cell current-clamp recordings in CA1 pyramidal neurons in acute hippocampal slices using standard electrophysiological techniques.Results: Mice experiencing both chronic sleep CSR and CSF showed a significant reduction in latency to GTC seizures compared to control animals (n=4, 203 14 sec vs. CSR [n=4, 168 21 sec, p<0.02] and CSF [n=4, 142 4 sec, p<0.003]). ASD had no effect on latency (n=4, 205 16 sec, p=0.93) but appeared to increase seizure severity, duration and recovery time. Only the CSF group showed a significant decrease in latency to the first MJ (control, n=4, 157 7 sec vs. ASD [n=4: 144 4 sec, p=0.13] and CSR [n=4, 136 16 sec, p=0.26] and CSF [n=4, 133 3 sec, p<0.02]). In preliminary whole-cell experiments, smaller average current injections were required to reach 50% of the maximum firing rate after ASD treatment (115 64 pA, n=2) than in controls (150 14 pA, n=2), consistent with an elevation of intrinsic excitability in CA1 neurons.Conclusions: Threshold to fluorothyl seizure induction was inversely related to the intensity of the sleep deprivation protocol such that longer daily sleep deprivation increasingly shortened latency to GTC seizures, suggesting that long-term sleep disruption may increase excitability in neuronal circuits. Further work is necessary to determine the cellular, synaptic and network mechanisms of this effect.