Abstracts

Rationale: Acute hippocampal slices positioned on multi-electrode arrays (MEAs) have increasingly been employed to better understand network activity across an entire brain slice under normal or pathological conditions. This platform also permits the identification of novel anti-seizure medications through in vitro drug screening [1]. The signal-to-noise ratio (SNR) rendered by MEAs is, however, often of poor quality and therefore does not permit detailed analysis of the signal recorded. Further, traditional MEA planar electrodes only record neural activity from the bottom of the slice, where cells damaged during brain slicing are located, and cannot resolve activity of single neurons activity embedded in a network. Here, we show that neural network activity from and across intact mammalian brain slices can be recorded using advanced three-dimensional multi-electrode arrays designed to measure activity in the mV range. Compared to other reported and commercially available 3-dimensional devices [2, 3], these novel electrodes permit a SNR up to 500% higher and offers new perspectives for in-vitro screening tools for potential anticonvulsants. Methods: Brains from mice aged postnatal day 35 (P35) were placed in an ice-cold carboxygenated (95% O2 and 5% CO2) artificial cerebrospinal fluid (aCSF), before being sliced at thicknesses ranging from 350m to 500m. Spike-shaped three-dimensional electrodes were manufactured and had controlled heights ranging from 100m to 350m, with tips devoid of insulating coating to allow direct interfacing with neural cells located inside the slices. After recovery (28C for 1.5 h), slices were positioned on the MEA in a high potassium (8.5 mM) aCSF solution and interfaced with the 3-dimensional micro-electrodes using an anchor (Figure 1). Results: Spontaneous neural activity (consisting of inter-ictal, bursting and ictal events) was recorded in vitro consistently at multiple electrode sites across the brain slice (Figure 2). The SNR was then compared between our three-dimensional micro-electrodes and earlier reported devices, including other three-dimensional (e.g. pyramidal-shaped) and planar micro-electrodes [3]. The average noise was reduced to 20V (compared to 40-60V with traditional micro-electrodes) and the highest recorded activity was in the mV range (up to 3.2mV). Compared to reported signal recordings in the current literature [3], this represents a significantly higher signal-to-noise ratio (over 500% better) than most commercially available devices. Conclusions: Our novel three-dimensional electrodes offer new opportunities to record neural network phenomena across and from within brain slices by increasing the resolution of the SNR and enabling the analysis of specific seizure-like events. We believe that this technology will provide researchers with a high definition tool and will facilitate the screening of anti-seizure compounds in brain slices derived from epileptic tissues, whether from animal models or surgically-resected human specimens. 1. "Development of multi-electrode array screening for anticonvulsants in acute rat brain slices", A. J. Hill et al., Journal of Neuroscience Methods, 185, 246?"256 (2010) 2. "Metal-Transfer-Micromolded Three-Dimensional Microelectrode Arrays for in-vitro Brain-Slice Recordings", S. Rajaraman et al., Journal of microelectrochemical systems, 20, 2 (2011) 3. "Multi-electrode array technologies for neuroscience and cardiology", M. E. Spira and A. Hai, Nature Nanotechnology, 8 (2013) Funding: The authors wish to thank the following for supporting this work: Dr. L. Belototski, E. Zailer, NSERC, CIHR, AMIF, CMC Microsystems and the Antje Graupe Pryor Foundation.