Combined electrophysiological and biosensor approaches to study purinergic regulation of epileptiform activity in cortical tissue

Abstract

Abstract:Background: Cortical brain slices offer a readily accessible experimental model of a region of the brain commonly affected by epilepsy. The diversity of recording techniques, seizure-promoting protocols and mutant mouse models provides a rich diversity of avenues of investigation, which is facilitated by the regular arrangement of distinct neuronal populations and afferent fibre pathways, particularly in the hippocampus. New method & Results:We have been interested in the regulation of seizure activity in hippocampal and neocortical slices by the purines, adenosine and ATP. Via the use of microelectrode biosensors we have been able to measure the release of these important neuroactive compounds simultaneously with on-going epileptiform activity, even of brief durations. In addition, detailed numerical analysis and computational modelling has produced new insights into the kinetics and spatial distribution of elevations in purine concentration that occur during seizure activity. Comparison and Conclusions:Such an approach allows the spatio-temporal characteristics of neurotransmitter/neuromodulator release to be directly correlated with electrophysiological measures of synaptic and seizure activity, and can provide greater insight into the role of purines in epilepsy.

Modeling microelectrode biosensors: free-flow calibration can substantially underestimate tissue concentrations

“…A biosensor is typically calibrated by placing it in a free-flow environment in which the analyte A has a fixed concentration $A_{\mathrm{c}}^{*}$ at its outer surface (Frenguelli and Wall 2016). As the analyte is absorbed into the biosensor enzyme layer, it diffuses until it is broken down by the enzyme at a rate v b into a certain number of molecules of the electrically active product H 2 O 2 , the concentration of which we denote by H .…”

“…The idealized model of a biosensor considered here with a single-enzyme layer is likely to display the same characteristics as the more complex biosensors such as those that use a cascade of enzymes for adenosine or inosine (Llaudet et al 2003; Wall and Richardson 2015; Frenguelli and Wall 2016), glutamate (Mikeladze et al 2002), or acetylcholine (Chen et al 1998). The main barrier for such analysis is the paucity of published information regarding the properties of the biosensors, which in many cases is proprietary.…”

“…Biosensors have been used to measure neurotransmitters and neuromodulators including glutamate (Hu et al 1994; Oldenziel et al 2006; Tian et al 2009), acetylcholine (Bruno et al 2006; Zhang et al 2010), adenosine triphosphate (Llaudet et al 2005; Frenguelli et al 2007; Gourine et al 2008; Lalo et al 2014; Lopatář et al 2015; Wells et al 2015), glucose (Lowry et al 1998; Dash et al 2013), adenosine, inosine, and hypoxanthine (Llaudet et al 2003; Klyuch et al 2012; Dale 2013; Van Gompel et al 2014; Wall and Richardson 2015; Frenguelli and Wall 2016). Many microelectrode biosensors developed for brain tissue use oxidative enzymes followed by detection via fixed-potential amperometry.…”

“…The biosensor is calibrated in a standard concentration of analyte, typically in free-flow conditions where the concentration of the analyte at the outer surface of the biosensor can be considered constant because any analyte broken down by the biosensor is rapidly replaced. Details of biosensor calibration are discussed in Frenguelli and Wall (2016). The free-flow calibration conditions differ substantially to those in tissue, where the analyte diffuses to reach the biosensor.…”

The combination of ribose and adenine promotes adenosine release and attenuates the intensity and frequency of epileptiform activity in hippocampal slices: Evidence for the rapid depletion of cellular ATP during electrographic seizures

“…). During seizure activity the extracellular accumulation of adenosine (During and Spencer ; Dunwiddie ; Dale and Frenguelli ) likely results from rapid, potentially very local (Wall and Richardson ; Frenguelli and Wall ), intracellular depletion of ATP, as well as the extracellular metabolism of ATP released in an activity‐dependent manner (Dale and Frenguelli ). Under both these conditions, the activation of adenosine A 1 receptors suppresses neuronal activity in an attempt to minimize cellular energy demand.…”