Figure 2.
Recording of sniffs and extracellular voltage in the mitral cell layer and light-elicited stimulation of ChR2 expressed in the axons of OSNs. a, Optotetrodes. Left, The combination of a guide glass tube and tetrodes was inserted into the mitral cell layer of the OB to allow recording of M/T cell activity and light stimulation of glomerular ChR2. Center, View of the optotetrode attached to the EIB-16 electrode interface. Right, Higher magnification view of the tip of the tetrodes and the glass guide for the optic fiber. The tip of the tetrodes is ∼0.2–0.3 mm longer than the fiber. b, Example of raw recording of extracellular potential and voltage changes recorded by the pressure sensor measuring nose pressure. Light was turned on at times shown by the trace labeled Sti. c, Two units separated from the data in b using Spike2 software. Left, Voltage variation for the two units. Right, Separation of the two units using principal component analysis. d, Three examples of the effect of light stimulation on spike firing by M/Ts. From left to right: Excitatory response, inhibitory response, and no response. Above, Raster for 60 trials; below. PSTH. Blue bars represent light stimulation (60 ms). e, Light pulses are not synchronized with the sniff. Top, Average voltage recording with the pressure sensor detecting pressure inside the nose for 681 sniffs taking place during light activation. Bottom, Bar graph showing the timing of light activation in the same time interval. A Rayleigh test for the significance of the mean direction in a histogram indicated that there was no specific distribution for this bar graph (p > 0.05).