A) Example of a coronal slice used for recording showing GAD67-GFP positive interneurons (left) and widespread expression ChIEF-tdTomato expression (right) throughout dLGN. B) Confocal image stack of an interneuron filled with biocytin during recording. Scale bars = 25 µm. C) Whole-cell current (top trace, Vm = −70 mV) and voltage (bottom trace, VH = −70 mV) clamp recordings from an LGN interneuron showing that repetitive photostimulation of CT fibers (10 Hz, 50 pulses; blue bars), produced a slow rising depolarization and underlying inward current that peaked near the termination of stimulation. D) Graded depolarization (top trace) recorded from an interneuron (Vm = −70 mV) evoked by a 10 Hz train of blue light pulses (50 pulses, blue bars). Expanded trace (below) illustrates the small unitary EPSPs that ride the crest of the slower depolarization. Bath application of TTX (1 µM), abolished both the graded depolarization and unitary EPSPs (bottom trace). E) Example of another response evoked by repetitive stimulation (20 Hz, 50 pulses, top trace). Bath application of NBQX (10 µM) significantly reduced the amplitude of depolarization (middle trace). The addition of APV (50 µM) had a negligible effect on the remaining depolarization (bottom trace). F) Excitatory response evoked by 20 Hz repetitive stimulation (50 pulses, top trace, Vm = −70 mV). Although bath application of NBQX (10 µM) and APV (50 µM) greatly reduced the response (middle trace), the addition of the Group I mGluR antagonists, MTEP and LY367381 had a no effect on the remaining depolarization (bottom trace). G) Summary plot of pharmacology experiments showing the mean reduction (±SEM) in the magnitude of the graded depolarization (pA x ms) expressed as a percentage of the control response. Application of NBQX reduced the response (n = 6) whereas the addition of APV (n = 7), or the Group I mGluR antagonists MTEP and LY367385 (n = 3) did not have any further effect on the remaining depolarization. (*p<0.05).