High resolution recording of local field currents simultaneously with sound-evoked calcium signals by a photometric patch electrode in the auditory cortex field L of the chick

Abstract

BackgroundFunctioning of the brain is based on both electrical and metabolic activity of neural ensembles. Accordingly, it would be useful to measure intracellular metabolic signaling simultaneously with electrical activity in the brain in vivo. New methodWe innovated a PhotoMetric-patch-Electrode (PME) recording system that has a high temporal resolution incorporating a photomultiplier tube as a light detector. The PME is fabricated from a quartz glass capillary to transmit light as a light guide, and it can detect electrical signals as a patch electrode simultaneously with a fluorescence signal. ResultsWe measured the sound-evoked Local Field Current (LFC) and fluorescence Ca2+ signal from neurons labeled with Ca2+-sensitive dye Oregon Green BAPTA1 in field L, the avian auditory cortex. Sound stimulation evoked multi-unit spike bursts and Ca2+ signals, and enhanced the fluctuation of LFC. After a brief sound stimulation, the cross-correlation between LFC and Ca2+ signal was prolonged. D-AP5 (antagonist for NMDA receptors) suppressed the sound-evoked Ca2+ signal when applied locally by pressure from the tip of PME. Comparison with existing methodsIn contrast to existing multiphoton imaging or optical fiber recording methods, the PME is a patch electrode pulled simply from a quartz glass capillary and can measure fluorescence signals at the tip simultaneously with electrical signal at any depth of the brain structure. ConclusionThe PME is devised to record electrical and optical signals simultaneously with high temporal resolution. Moreover, it can inject chemical agents dissolved in the tip-filling medium locally by pressure, allowing manipulation of neural activity pharmacologically.