Optogenetic excitation of ventral tegmental area (VTA) dopaminergic neurons augments place cells’ spiking.

(A) Atlas schematic shows optic fiber and tetrodes in the VTA or hippocampal CA1. Images below show channelrhodopsin 2 with yellow fluorescent protein (ChR2-YFP) expression, tyrosine hydroxylase (TH) staining, and their overlay in VTA of TH::Cre rats injected with E123T/T159C virus. (B) Raster plot from 40 repetitions (above) and firing frequency (below) of optically evoked time-locked excitation of a VTA slow-spiking cell. (C) Raster plot from 40 repetitions (above) and spike count of 120 repetitions (below) of a sample place cell. Time 0 indicates the onset of the stimulation protocol. (D) Firing rate of 22 place cells 100 ms after the onset of the stimulation protocol expressed as a percentage of the prestimulation values, for control (left bar) and photostimulation (middle bar), paired t test: t(21) = −3.910, ***p < 0.001; the right bar shows the firing rate (% prestimulation) for 250 ms after photostimulation onset, paired t test: t(21) = −1.767, p = 0.092. Error bars, mean ± SEM. (E) Raster plot and spike count of a slow-spiking interneuron. (F) Spiking cross correlogram between the place cell and the interneuron shown in (C) and (E), respectively. (G) Firing rate of 21 interneurons 100 ms after photostimulation (% prestimulation), for control (left bar) and photostimulation, paired t test: t(20) = 3.002, **p = 0.007. The right bar shows the firing rate for 250 ms after photostimulation onset, paired t test: t(20) = 6.841, ***p < 0.001. Error bars, mean ± SEM. Files dataset is available at Figshare public repository in Tsanov 2016 data / E123T electrophysiology and E123T immunohistology folders https://figshare.com/s/b86a9a111353ba04bd32.