Figure 1.
Odor stimulation evokes an LFP response specific to a single glomerulus. A, The field potential recording pipette (filled with Oregon Green), was precisely placed in the center of the labeled glomerulus under visual control using TPLSM. In the GL, odor- evoked LFP responses that consisted of rapid and repetitive negativities locked to respiration. Note that LFP responses evoked by four successive applications of benzaldehyde (0.5%) were very similar. Occasionally β oscillations were recorded (inset, star). B, Odor-evoked fast negativities were exclusive to the glomerular volume. Unlike the field potential negativity evoked by nerve stimulation (C), odor-evoked fast negativities (same as in A) disappeared in the EPL a few tens of micrometers below the GL, leaving a slow and long-lasting negativity. Inset shows another recording in which brief application of two different odors [almond, 0.5% and propionic acid (PA), 0.3%] evoked rapid negativities followed by slower ones of various shapes. Rapid negativities also disappeared, and the slower ones diminished in the EPL. C, Depth profile of LFP responses to olfactory nerve stimulation. D, LFP responses to 2-butanol (0.5%) were glomerular-specific and showed little volume conduction. E, Glutamate receptor antagonist NBQX (250 μm dissolved in fluorescent saline) blocked LFP responses to limonene (0.4%). TPLSM was used to image drug diffusion within glomerulus boundaries. Partial (first application) and full block (second application) occurred within seconds after application. ONL, Olfactory nerve layer; MCL, mitral cell layer; GCL, granule cell layer.