Figure 4. Glomerular layer targeting of feedback inputs is unrelated to glomerular odor specificity.

A) Schematic. B₁) Intrinsic signal optical imaging from one mouse showing glomerular responses to three different odors (Ethyl tiglate (ET), Anisole (Ani), 2-Hexanone (Hex)) and the activity map superimposed on the olfactory bulb surface vasculature (bottom right). Colored circles highlight activated glomeruli; boxes represent fields selected for bouton imaging. Field 1 is centered over a glomerulus responding to ethyl tiglate and Field 2 indicates a region without a response to the odors. B₂) Targeted 2-photon imaging beneath an identified glomerulus. Top, blow up of region around Field 1 from B₁ showing overlay of intrinsic optical signal (red, ethyl tiglate) and surface vasculature. Bottom, 2-photon image stack of Texas red dextran-filled vessels aligned with the vasculature in the image above. B₃) Map of glomerular layer boutons responding with excitation within fields indicated in B₁. Colors indicate boutons responding selectively to individual odors (red, green, blue), boutons with overlapping responses to two odors (yellow, magenta, cyan), and boutons responsive to all three (white). ROIs are shown enlarged for clarity. B₄) Numbers of boutons responding with excitation to each odor for the fields in B₃. C) Summary of results (mean ± SEM) from all experiments using three odors indicates that individual odors were equally likely to activate boutons regardless of the responses of the overlying glomerulus. We calculated a variation index for each odor ((Observed fraction of responsive boutons / 0.33) – 1) for fields centered on an odor-responsive glomerulus (white circles) and fields within regions that did not show a glomerular response to any of the three odors (black circles). Variation index=0 if each odor (1 out of 3) has an equal probability of eliciting bouton responses in an imaging field. Odors were grouped between those that did (Glom+) or did not (Glom-) activate the odor-responsive glomerulus. In all cases, odors consistently had a variation index near zero.