Integration of light-controlled neuronal firing and fast circuit imaging

Abstract

For understanding normal and pathological circuit function, capitalizing on the full potential of recent advances in fast optical neural circuit control will depend crucially on fast, intact-circuit readout technology. First, millisecond-scale optical control will be best leveraged with simultaneous millisecond-scale optical imaging. Second, both fast circuit control and imaging should be adaptable to intact-circuit preparations from normal and diseased subjects. Here we illustrate integration of fast optical circuit control and fast circuit imaging, review recent work demonstrating utility of applying fast imaging to quantifying activity flow in disease models, and discuss integration of diverse optogenetic and chemical genetic tools that have been developed to precisely control the activity of genetically specified neural populations. Together these neuroengineering advances raise the exciting prospect of determining the role-specific cell types play in modulating neural activity flow in neuropsychiatric disease.

Figure 1. Design for integrating fast optical control and recording technologies

a) Voltage-sensitive absorption band of RH-155 overlaid on action spectra of ChR2, NpHR; spectral separation suggests that high-speed all-optical control and recording of neural activity flow can be conducted with this combination of optical tools. b) Schematic of microscopy apparatus for high-speed all-optical control and recording of circuit activity.

Figure 2. Experimental integration of high-speed all-optical circuit control and imaging

a) Top: (Left to right) Brightfield: image showing a 350μm horizontal hippocampal slice prepared from a Thy1::ChR2-YFP transgenic mouse (6wks) stained with RH-155 (0.1mg/mL for 3hrs). White boxes indicate sources of VSDI traces in CA1 and cortex (ctx); field recording electrode can be seen in upper middle region of image. Scale bar 350μm. YFP: image showing labeling of neurons with ChR2-YFP primarily in CA1 of hippocampus; same field as brightfield image. 5Hz, 20Hz: sample VSDI images of neural activity flow in CA1 and cortex following ChR2-mediated optical stimulation (10ms pulses of 470nm light delivered by the Sutter DG-4 high-speed optical switch); same field as brightfield and YFP images.Note the lack of optical signal in non-YFP expressing CA3; the optical signal seen in adjacent cortex is synaptically induced as shown in (b). Bottom: Single-pixel VSDI traces corresponding to white boxes for 5Hz (left) and 20Hz (right) optical stimulation. Blue dashes indicate timing of 10ms blue light pulses used to stimulate ChR2. Scale bars: 0.1%dF/F and 200ms. Insets: sample field recording traces for one optically stimulated event delivered in trains of 10 pulses at 5Hz (left) and 20Hz (right). Scale bars: 0.5mV and 20ms. b) Optical recording of optically-evoked neural activity flow following pharmacological modulation. Blue light directly stimulates CA1 neurons and triggers stimulation of adjacent cortex via excitatory synapses as CNQX (10μM) and D-APV (25μM) block cortical responses to optical stimulation determined by VSDI. Image scale bar: 350μm. VSDI trace scale bars: 0.1%dF/F and 200ms.

Figure 3

Experimental design for using high-speed all-optical control and recording to probe neuropsychiatric disease.