Figure 7.

PV+ interneurons contribute to feedforward inhibition of MSNs. A, Schematic of experimental design. PV-2A-Cre × D1-tdTomato mice were coinjected with AAV-CaMKII-ChR2-mCherry in the vHPC and AAV-CAG-FLEX-ArchT-GFP in the NAc. In each trial, ChR2 was activated with blue light to trigger vHPC inputs to D1+ MSNs or ArchT+ PV+ interneurons. In alternating trials, ArchT was also activated with yellow light to suppress the activity of ArchT+ PV+ interneurons. Colored bars indicate timing of ChR2 and ArchT activation. B, Current-clamp recording of ArchT+ PV+ interneurons showing vHPC-evoked spiking by activation of ChR2 (blue trace) that was blocked by simultaneous activation of ArchT (black trace). Right, Quantification of vHPC-evoked spiking, demonstrating effective suppression by ArchT. C, Left, Average vHPC-evoked EPSCs at D1+ MSNs at −70 mV, with (black trace) or without (red trace) suppression of PV+ interneurons. Right, Quantification of EPSC amplitude, shown as means ± SEM, where lines indicate single D1+ MSNs under the two conditions. D, Similar to C for vHPC-evoked IPSCs at +20 mV in the presence of CPP. Right, Normalized responses, showing reduction in feedforward IPSCs with suppression of PV+ interneurons. n.s., Not significant. **p < 0.01.