Genetically-controlled MRI contrast agents for functional brain imaging

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Understanding how the brain controls behavior is one of the outstanding scientific problems of today. The methods most needed to study neural mechanisms of behavior will combine the noninvasiveness and whole-brain coverage of magnetic resonance imaging (MRI) with the precision of cellular recording tech- niques like electrophysiology and fluorescence microscopy. Here we propose to develop a new set of neu- roimaging techniques that approach this ideal. The methods rely on the use of protein-based sensors that report aspects of neural function and may be targeted to specific cells or cell types. Unlike protein sensors developed previously for optical imaging, the sensors we propose to create will incorporate MRI contrast agents, meaning that they can be monitored across entire, intact brains; genetic targeting will allow neural activity of defined “circuit elements” to be identified and integrated into explanatory models of brain function. In the first two Specific Aims, we propose to form and apply genetically-encoded calcium-sensitive contrast agents based on the iron storage protein ferritin (Ft). Our preliminary data and recently published results indicate feasibility of the design, which we will test in rats once it has been validated in cell culture. Ft- based sensors may not offer enough sensitivity for functional imaging of sparse or subtle changes in neu- ronal physiology, however. To address this, we propose in Aims 3-4 to develop a second genetically- controlled system in which markers of neuronal activity are transduced and amplified by enzymes into ro- bust signals that may be read out using powerful exogenous contrast agents. This program is an ambitious and high-impact endeavor that, once accomplished, will change the way researchers study the brain. The PI and his laboratory have the diversity of experience, record of effective collaborations, and risk-taking spirit that will allow them to introduce a new generation of brain measurements and empirical approaches in neuroscience.