FIGURE 4.

Approach to measure both the input and output of the same glomeruli in the mouse olfactory bulb. (A) Experimental approach: Left, the olfactory receptor neuron nerve terminal input is labeled via nasal infusion of an organic calcium sensitive dextran dye together with a low concentration of Triton-X. In the same preparation, GEVIs or GECIs were targeted to mitral and tufted output cells using cre-dependent AAVs in a transgenic mouse that expressed cre recombinase in those cells. Right, input and output can be measured independently from the same glomerulus by using activity sensors with substantially different excitation or emission spectra. The signals from the two cell types can be distinguished by changing the excitation or emission wavelengths. (B) A doubled labeled histological section showing targeting to input vs. output. In this section, Cal-590 dextran was anatomically targeted to the olfactory receptor nerve terminal input (left) and ArcLight was genetically targeted via AAV injection to the mitral and tufted cell output (middle). The merged image is shown on the right. Both sensors are present in each glomerulus. onl, olfactory nerve layer; gl, glomerular layer; epl, external plexiform layer; mcl, mitral cell layer. Scale bar in panel (B), 50 μm. Modified from Storace and Cohen (2017).