Figure 2.

In vivo optogenetic tagging of MS ChAT-ChR2 neurons. A, Spike activities of a representative ChAT-ChR2 neuron (yellow ticks) recorded with tetrodes in a freely behaving mouse. Spike waveforms of two simultaneously recorded units (yellow and green) from one tetrode are shown. Ticks in each row represent waveform sequences recorded by one channel of the tetrode. Light-induced spikes are illustrated in the boxed area. Calibration: 5 s. B, Cluster separation of the two neurons depicted in A (yellow and green) in a 3D feature space. Average tetrode waveforms are shown in the gray boxed area with neuron identities labeled outside the box. Average waveforms of spontaneous and light-induced spikes are illustrated separately at the bottom. C, Raster plot activity of the entrained ChAT-ChR2 neuron in response to different optogenetic stimulation frequencies (5 ms pulses, blue bars). Calibration: 20 s. D, Top left, A microdrive recording array connected to a laser generator. Enlarged box shows the tip of the optrode. Top right, A ChAT-ChR2-EYFP mouse after recovery from electrode implantation surgery. Bottom, Electrode recording sites revealed by Nissl staining. Red arrowheads indicate the tips of the electrode bundles. E, Spontaneous and light-induced waveforms of six MS ChAT-ChR2 neurons recorded by tetrodes, not including the neuron shown in B (M14SC06). No significant change in waveforms is observed between spontaneous and light-induced spikes. Calibration: 1 ms, 0.2 mV.