Combined in Vivo Amperometric Oximetry and Electrophysiology in a Single Sensor: A Tool for Epilepsy Research
2017
Ledo, Ana | Lourenço, Cátia F. | Laranjinha, João | Gerhardt, Greg A. | Barbosa, Rui M.
Seizures are paroxysmal events in which increased neuronal activity is accompanied by an increase in localized energetic demand. The ability to simultaneously record electrical and chemical events using a single sensor poses a promising approach to identify seizure onset zones in the brain. In the present work, we used ceramic-based platinum microelectrode arrays (MEAs) to perform high-frequency amperometric recording of local pO₂ and local field potential (LFP)-related currents during seizures in the hippocampus of chronically implanted freely moving rats. Resting levels of O₂ in the rodent brain varied between 6.6 ± 0.7 μM in the dentate gyrus (DG) region of the hippocampus and 22.1 ± 4.9 μM in the cerebral cortex. We also observed an expected increase in hippocampal pO₂ (15 ± 4% from baseline) in response to tail pinch stress paradigm. Finally, induction of status epilepticus by intrahippocampal injection of pilocarpine induced biphasic changes in pO₂ in the hippocampus. The initial dip at seizure onset (ΔO₂ = −4.5 ± 0.7 μM) was followed by a prolonged hyperoxygenation phase (ΔO₂ = +10.4 ± 2.9 μM). By acquiring the amperometry signal with a high sampling rate of 100 Hz we decomposed the raw signal in an oximetry recording (<1 Hz) and LFP recording (>1 Hz), demonstrating that each individual Pt site can simultaneously report changes in local pO₂ and LFP-related currents during pilocarpine-induced seizure activity. This has high potential for translation into the clinical setting supported on intracranial grid or strip electrodes.
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