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. 2020 Jun 5;14:141. doi: 10.3389/fncel.2020.00141

FIGURE 3.

FIGURE 3

Cholinergic neuron (CN) optotagging in the basal forebrain (BF). (A) Confocal EYFP fluorescence for a sagittal brain section of a ChAT-EYFP-ChR2 mouse (inset: BF at 63× magnification, bar 10 μm); arrow: fluorescence along the membrane; OB, olfactory bulb). (B) Light pulses (50 ms, blue trace) increase the extracellular spiking activity of neurons in ChAT-ChR2 animals but not in ChAT-Cre controls (inset: response to one light pulse). (C) Representative traces of in vitro voltage clamp recordings of a ChAT-ChR2+ neuron (top) and ChR2– neuron (bottom) after light stimulation (blue). Red trace shows the average response. (D) Representative traces of in vitro whole cell current clamp recordings of ChAT-ChR2+ (n = 7, 7/7 responded to 1 ms Lstim) and ChR2– neurons (n = 9, 3/9 responded to Lstim). Notice the jitter of the response of the synaptically connected ChR2– neuron. (E) Left, latency of light activation of ChR2+ (4.1 ± 0.4 ms) and ChR2– neurons (18.1 ± 3.5 ms, t test, *p < 0.001). Red line: criterion for a neuron to be considered cholinergic. Right, latency histogram of all neurons recorded in vivo (green: latency <10 ms). (F) Scatter plot (top, 20 trials, bar, 1 s) and peristimulus time histogram (PSTH) (bottom, bars, 1 s and 20 Hz) of an identified cholinergic neuron to 10 pulses of a light stimulation at 5 Hz (see criteria in the text).