Microfluidic Brain Slice Chambers and Flexible Microelectrode Arrays for in vitro Localized Stimulation and Spatial Mapping of Neural Activities
In vitro neurobiological experiments using brain slices have played a key role in improving our understanding of the central nervous system. Microfabricated brain slice chambers and flexible semi-transparent multi-electrode arrays allow controlled local changes in the chemical environments as well as high resolution electrophysiology and optical recording of brain slices which would in turn provide further information of the complex neuronal system. In this study, we exploit the advantages of microfabricated devices, including a microfluidic brain slice chamber for localized chemical stimulation and a flexible microelectrode array for spatial mapping of neuronal activities, to investigate various biophysical properties of cortical spreading depression.
First, a microfluidic brain slice chamber is designed and fabricated to permit localized chemical stimulation to specific brain slice cortical regions. We build a numerical finite element model to predict the injected plume shape and the resulting ion distributions in the stimulated brain slice. Various characterization methods, including particle tracking velocimetry, fluorescent imaging and tissue staining, are implemented to verify the fluid dynamics predicted by our model. With the ability to fine control the stimulation area, we vary the stimulation size as well as the extracellular potassium concentration ([K+]e) to study the conditions for the onset of cortical spreading depression. We find a strong correlation between the threshold concentration and the slice area exposed to the increased [K+]e. Our results show that CSD is inducible under the conditions expected in migraine aura.
We then explore the use of a flexible microelectrode array to map spatiotemporal electrophysiological activities induced by localized chemical stimulation. We concurrently use the microfluidic device to initiate CSD in mice cortex and the electrode array to record electrical activities accompanying the spreading wave. Besides the consistency between optical and electrical recording, we observe the electrical responses similar to cortical spreading convulsion with a corresponding optical characteristic.
In summary, the microfluidic brain slice chamber has been demonstrated with a localized stimulation capability and used to probe the cortical spreading depression initiation and propagation properties. The concurrent use of the microfluidic and microelectrode array techniques has been demonstrated and is shown to be promising in addressing scientific questions. Our work demonstrates a successful implementation of novel microfabricated tools for the neuroscience research.