Rapidly inducible, genetically targeted inactivation of neural and synaptic activity in vivo

Abstract

Inducible and reversible perturbation of the activity of selected neurons in vivo is critical to understanding the dynamics of brain circuits. Several genetically encoded systems for rapid inducible neuronal silencing have been developed in the past few years offering an arsenal of tools for in vivo experiments. Some systems are based on ion-channels or pumps, others on G protein coupled receptors, and yet others on modified presynaptic proteins. Inducers range from light to small molecules to peptides. This diversity results in differences in the various parameters that may determine the applicability of each tool to a particular biological question. Although further development would be beneficial, the current silencing tool kit already provides the ability to make specific perturbations of circuit function in behaving animals.

Figure 1

Schematics of four rapidly inducible and reversible, genetically encoded neuronal inactivation systems described here. A, Allatostatin receptor (AlstR; green) couples of the binding of allatostatin (red spheres) to the activation of a G-protein (white). This then leads to the opening of a G-protein couples inward rectifier K+ channel (blue). B, The two subunit GluClα/β receptor (blue, purple) is opened by ivermectin (black circle). The resulting Cl− current suppresses neuronal activity. C, Chloride current through the five subunit GABA_A channel is enhanced by binding of zolpidem (black circle) to the interface between γ2 and α1 subunits leading to suppression of excitability. D, Two Molecular Systems for the Inactivation of Synaptic Transmission (MISTs). The one component system is based on crosslinking of modified VAMP (light blue). The two component system is based on mislocalization of modified Synaptophysin (Sph; purple) non-specifically along the plasma membrane using the transmembrane domain of Syntaxin (StxTM). E, Halorhodopsin (NpHR) pumps chloride into the cell when opened by yellow light.

Figure 2

Time course of the induction and reversal of inactivation for the four neuronal silencing systems