Remote Control of Neuronal Signaling in vivo

A significant challenge for neuroscientists is to determine how both electrical and chemical signals affect the activity of cells and circuits and how the nervous system subsequently translates that activity into behavior. Remote, bidirectional manipulation of those signals with high spatiotemporal precision is an ideal approach to addressing that challenge. Recently, neuroscientists have developed a diverse set of tools that permit such experimental manipulation with varying degrees of spatial, temporal, and directional control. These tools use light, peptides, and small molecules to primarily activate ion channels and G protein-coupled receptors (GPCRs) that in turn activate or inhibit neuronal firing. By monitoring the electrophysiological, biochemical, and behavioral effects of such activation/inhibition, researchers can better understand the links between brain activity and behavior. The research in this thesis centers on using a class of designer GPCRs, termed Designer Receptors Exclusively Activated by Designer Drugs (DREADDs), to remotely and non-invasively control the activity of particular neuronal populations. DREADDs are evolved muscarinic receptors that selectively respond to the otherwise inert compound clozapine-N-oxide (CNO) and not to their native ligand, acetylcholine. Using a chemical-genetic approach, I demonstrate that the Gq-coupled DREADD (hM3Dq), which is derived from the human muscarinic M3 receptor, can be used to activate neuronal firing selectively in the cortex and hippocampus of mice expressing hM3Dq. The neuronal activation subsequently results in behavioral and electrophysiological changes. Then, I use those behavioral changes as a readout to examine the underlying neurocircuitry and discuss the findings in the context of psychosis. The tools for remote control of neuronal activity, including DREADDs, differ in the direction of their effect (activation/inhibition, hyperpolarization/depolarization), their onset and offset kinetics (milliseconds/minutes/hours), the degree of spatial resolution they afford, and their invasiveness. While none of these tools is perfect, they each have advantages and disadvantages, which I describe, and they are all still works-in-progress. I conclude with a discussion of the clinical and translational applications of these technologies and provide suggestions for improving upon the existing tools.Doctor of Philosoph