Figure 2. GP-FC cells modulate FC firing rates in vivo.
a–b. ChR2 stimulation or ArchT inhibition of Vgat i-Cre GP somata bidirectionally modulates firing rates in FC. Left, Schematic showing extracellular recordings in FC during optical stimulation of ChAT+ (axons shown in magenta) and ChAT− (axons shown in black) in GP with pulsed 473 nm (5ms pulses, 10 Hz for 3s, a) or constant 594 nm (3s, b) illumination. The mixed ChAT+/ChAT− GP-FC projection appears striped. Middle left, mean firing rate (±sem) of all FC units in response to 473 nm stimulation (a) of ChR2+ (blue; n=90 units, 5 mice) or control (black; n=99 units, 3 mice) mice or 594 nm stimulation (b) of ArchT+ (yellow; n=96 units, 3 mice) or control mCherry+ (black; n=63, 2 mice) mice (ChAT i-Cre mice expressing mCherry in GP). Middle right, histogram of indices of light modulation (Ilight) of FC unit firing rates (f), calculated as (f Light On − f Light Off)/(f Light On + f Light Off). Red bars indicate significantly modulated units (P<0.05, T-Test). ChR2+ stimulation excited 4 and inhibited 38 units; ArchT+ stimulation excited 25 and inhibited 19 units. Insets, example units, scale bar 5 Hz/1 s. Right, pseudocolored plot of changes in f for each unit, normalized to the baseline period and ordered by ILight. c. Pulsed (as in a) ChR2 stimulation of Vgat i-Cre GP axons in FC increases firing rates on a millisecond time scale. Left, Schematic shown optrode placement in FC used for stimulation and recording. Right, mean (±sem) Z-scored firing rates after each 5ms light pulse (blue rectangle) relative to equivalent baseline period 3s prior (ChR2+, n=111, 5 mice; mCherry+, n=92, 2 mice). d. Pulsed ChR2 depolarization of ChAT i-Cre GP somata increases firing rates in FC. Left, experimental schematic (as in a). Middle, histogram of Ilight for FC units (as in a), ChR2+ excited 15 and inhibited 2 of 120 units from 4 mice. Right, pseudocolored plot of changes in firing rate for all units.