Abstract
Highlights Simultaneous epileptiform LFPs and single-cell activity can be recorded in the membrane chamber.Interneuron firing can be linked to epileptiform high frequency activity.Fast ripples, unique to chronic epilepsy, can be modeled in ex vivo tissue from TeNT-treated rats.Traditionally, visually-guided patch clamp in brain slices using submerged recording conditions has been required to characterize the activity of individual neurons. However, due to limited oxygen availability, submerged conditions truncate fast network oscillations including epileptiform activity. Thus, it is technically challenging to study the contribution of individual identified neurons to fast network activity. The membrane chamber is a submerged-style recording chamber, modified to enhance oxygen supply to the slice, which we use to demonstrate the ability to record single-cell activity during in vitro epilepsy. We elicited epileptiform activity using 9 mM potassium and simultaneously recorded from fluorescently labeled interneurons. Epileptiform discharges were more reliable than in standard submerged conditions. During these synchronous discharges interneuron firing frequency increased and action potential amplitude progressively decreased. The firing of 15 interneurons was significantly correlated with epileptiform high frequency activity (HFA; ~100–500 Hz) cycles. We also recorded epileptiform activity in tissue prepared from chronically epileptic rats, treated with intrahippocampal tetanus neurotoxin. Four of these slices generated fast ripple activity, unique to chronic epilepsy. We showed the membrane chamber is a promising new in vitro environment facilitating patch clamp recordings in acute epilepsy models. Further, we showed that chronic epilepsy can be better modeled using ex vivo brain slices. These findings demonstrate that the membrane chamber facilitates previously challenging investigations into the neuronal correlates of epileptiform activity in vitro.
Highlights
A major issue in studies of epilepsy is how much the activity of different types of neurons is altered during epileptiform bursts
We began by testing the ability of the membrane chamber to support epileptiform network activity, using the elevated potassium model in vitro (Traynelis and Dingledine, 1988)
We tested whether the membrane chamber provided a viable environment for the simultaneous recording of single-cell activity in patch clamp and epileptiform field activity
Summary
A major issue in studies of epilepsy is how much the activity of different types of neurons is altered during epileptiform bursts. Acute manipulations which can induce epileptiform activity include perfusion with solutions containing elevated potassium (Traynelis and Dingledine, 1988), lowered calcium (Jefferys and Haas, 1982) or zero magnesium (Mody et al, 1987) Such experiments are advantageous as they permit the recording of neuronal network activity with microelectrode techniques whilst perfusing with pharmacological agents (Hill and Greenfield, 2011). Guided patch clamp can be performed using a submerged style chamber, in which the slice rests on a plastic cover slip within a deeper reservoir of aCSF (Li and McIlwain, 1957) This permits the use of high powered objectives, it severely impairs oxygen delivery to the slice, which impacts on the ability to record robust local field potentials (LFPs) (Gloveli et al, 2005; Hájos et al, 2009). Suspension of the slice on a net has been suggested to impair high-powered imaging (Hill and Greenfield, 2011)
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