CALIFORNIA INSTITUTE OF TECHNOLOGY
This project develops tools to address two hypotheses: first that specific types of neurons in localized brain regions or subregions can be altered so that they are susceptible to reversible inactivation or activation in response to systemically delivered low-toxicity chemicals or drugs; and second, that neuronal development, differentiation, and migration can be studied via manipulating ion fluxes, including calcium fluxes, which then lead to diverse signal transduction events. Reagents will be
generated that can achieve adjustable, reversible, cell-specific, electrophysiologically measurable, and non-antigenic manipulation of neuronal excitability, and of Ca-activated signal transduction within neurons. Development will continue on a small repertoire of ligand-activated channels, avermectin receptors (AVMRs), that can be expressed in target neurons. These channels will be developed by systematically mutating subunits of existing pentameric Cys-loop receptors: the C. elegans GluCl alp
ha and beta subunits, and the human glycine receptor. The channels will be insensitive to endogenous ligands (such as neurotransmitters), but will be activated dose-dependently by ivermectin and its analogs, widely used drugs that can be given orally or by injection into the periphery. The chloride-permeable AVMR-Cl will be used as a starting point for constructing AVMR-Na and AVMR-Ca, sodium- and calcium-permeable versions of these channels. The "therapeutic or research index" of the
AVMR system will be improved by finding an AVM analog with fewer CNS side effects, by increasing the AVM sensitivity of the existing optimized GluCl subunits, or by increasing the channel open time or conductance of the existing GluCl subunits, while maintaining reversibility. The project will also avoid immune reactions to AVMR proteins by generating a human glycine receptor-based version. The AVMRs will be useful for research in many vertebrate species: there will be considerable impact for re
search on circuit analysis; controlling differentiation, neurogenesis, and migration; models for excitotoxicity; and glial activation. Therapeutic impacts include "pharmacological deep-brain stimulation"; neuroprotection; and other uses that extend beyond CNS neuroscience. PUBLIC HEALTH RELEVANCE: This project continues to use receptor ion channels to gain new insight into how neurons are connected within circuits and how such circuits control behavior. We will engineer new receptor ch
annels that respond only to drugs, avermectins, that can be delivered in an animal's diet. Once these receptors are developed, it will be possible to study how activating or inhibiting selected neurons influences behavior. Ultimately, such procedures, involving both gene therapy and an FDA-approved set of drugs, could also help normalize neurons that are either too active, or not active enough, in psychiatric diseases.