The brain slice preparation has provided amazing access to details of cellular and circuit level brain function. There are many classes of questions that can only be addressed using the brain slice, but controlling the spatial and temporal neurochemical microenvironment during experiments is difficult using standard bath exchange laminar flow slice chambers. In our work we are exploring how dopamine (DA) and other neuromodulators might influence the ability of the prefrontal cortical microcircuit to maintain spatiotemporal activity patterns associated with working memory, cognitive flexibility and other executive functions. Years of research have demonstrated the relevance of dysfunction of DA to cognitive function - for example in Schizophrenia where DA signaling is thought to be impaired through unknown mechanisms or in Parkinson's disease where DA innervation to cortex from the ventral tegmental area (VTA) is lost. We would like to be able to apply neurochemicals such as DA to different areas of the same slice under precise temporal and spatial control in order to explore effects on network activity in a way that is relevant to the intact brain. Currently, we are limited to exchanging the bathing medium over the whole slice or puffing compounds onto or into the slice using pipettes, which impede electrophysiological and imaging access and are not well controlled. A more precise and versatile method would be invaluable for us and for many others doing brain slice physiology. We have created a prototype microfluidic brain slice device (5BSD) that marries an off-the shelf brain slice chamber with an array of microfluidic channels set into the bottom surface of the chamber (www.jove.com/index/Details.stp?ID=302). This device is created using rapid prototyping and, once optimized, it is trivial to replicate and share the devices with other investigators. Additionally, our 5BSD integrates seamlessly into standard physiology/imaging chambers, it is immediately available to the whole slice physiology community. With this technology we can address the flow of neurochemicals and any other soluble factors to precise locations in the brain slice with the temporal profile we choose. We are interested specifically in DA and we can quantify DA delivery in tissue using cyclic voltammetry (CV). Therefore we will use DA delivery to mouse cortex for our 2 specific aims - one to refine and develop the technology further and the other to test the effects of DA on cortical activity patterns.
Our approach will offer a novel, sophisticated approach to test the effects of modulatory neurotransmitter and their antagonists on the circuit dynamics in diseases as diverse as schizophrenia and Parkinson's disease. It is difficult to imagine a better way of understanding how the cortical microcircuit works than by directly imaging its function while controlling the neurochemcial microenvironment. We envision that our work here will lead to a whole class of devices that will allow researchers to control the microenvironment of the brain slice preparation to address a variety of questions and that our efforts to integrate into currently used chamber technology will set a standard for other such efforts to be easily and immediately available for physiologists
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