Figure 2. Identifying serotonergic neurons.
(A) Example voltage trace from 10 pulses of 10-Hz light stimulation (cyan bars; light duration, 5 ms). Each light-triggered spike is shown below. The lower right is the first two principal components of all waveforms from one tetrode wire, showing the neuron's (‘unit’) isolation quality, with 100 randomly-chosen light-evoked spikes in cyan. (B) Quantification of light-evoked responses to identify serotonergic neurons (filled points). Abscissa: energy (integral of the squared voltage values) of the light-evoked response from each neuron. Ordinate: Euclidean distance between the mean spontaneous spike and the light-evoked response. Example neurons are shown to the right (black, spontaneous spikes; cyan, light-evoked voltages; SD of spike waveforms are smaller than line thicknesses). Note that three unfilled points in the lower-right cluster are not considered identified serotonergic neurons because of low probability of firing in response to light stimulation. (C) Mean and SD of the light-evoked spike latency for identified serotonergic neurons. Probability (D) and latency (E) of light-evoked spikes from serotonergic neurons as a function of stimulation frequency (filled points are means across neurons).