No response was observed to laser pulses in the absence of MNI-glutamate. To express channelrhodopsin-2 (ChR2) in RGCs, we injected 1 l of AAV-2.1-syn-ChR2-GFP into each attention and brain slices were prepared 4C5 weeks later. spikes that reliably propagate to the soma/axon. Moclobemide whole-cell recordings expose that nearly every action potential evoked by visual stimuli has characteristics of spikes initiated in dendrites. Second, inhibitory input from a different class of SC neuron, horizontal cells, constrains the range of stimuli to which WF cells respond. Horizontal cells respond preferentially to the sudden appearance or quick movement of large stimuli. Optogenetic reduction of their activity reduces movement selectivity and broadens size tuning in WF cells by increasing the relative strength of reactions to stimuli that appear all of a sudden or cover a large region of space. Consequently, strongly propagating dendritic spikes enable small stimuli to drive spike output in WF cells and local inhibition helps restrict reactions to stimuli that are both small and moving. SIGNIFICANCE STATEMENT How do neurons respond selectively to some sensory stimuli but not others? In the visual system, a particularly relevant stimulus feature is definitely object motion, which often reveals additional animals. Here, we display how specific cells in the superior colliculus, one synapse downstream of the retina, respond selectively to object motion. These wide-field (WF) cells respond strongly to small objects that move slowly anywhere through a large region of space, but not to stationary objects or full-field motion. Action potential initiation in dendrites enables small stimuli to result in visual reactions and inhibitory input from cells that prefer large, suddenly appearing, or quickly moving stimuli restricts reactions of WF cells to objects that are small and moving. and electrophysiological recordings. For some experiments, we used the following transgenic mice: Ntsr1-GN209-Cre (Gerfen et al., 2013) crossed to Ai32 (Madisen et al., 2012), vGAT-ChR2 (Zhao et al., 2011), or Moclobemide Gad2-Cre (Taniguchi et al., 2011). electrophysiology, imaging, uncaging, and optogenetics. Four-hundred-micrometer-thick parasagittal mind slices were slice having a vibratome (Leica) in chilled trimming solution containing the following (in mm): 60 sucrose, 83 NaCl, 25 NaHCO3, 1.25 NaH2PO4, 2.5 KCl, 0.5 CaCl2, 6 MgCl2, 20 d-glucose, 3 Na pyruvate, and 1 ascorbic acid. Slices were transferred to warm (34C) trimming solution, which was then allowed to awesome to space temp. Approximately 60 min after trimming, slices were transferred to artificial CSF (ACSF) comprising the following (in mm): 125 NaCl, 25 NaHCO3, 1.25 NaH2PO4, 2.5 KCl, 1.3 CaCl2, 1 MgCl2, 20 d-glucose, 3 Na pyruvate, and 1 ascorbic acid for recording (at 32C) or further storage (at space temperature). Whole-cell current-clamp recordings were made with glass pipettes filled with the following (in mm): 134 K gluconate, 6 KCl, 4 NaCl, 10 HEPES, 2 MgATP, 0.4 NaGTP, 10 tris phosphocreatine, 0.05 Na Alexa Fluor 594 hydrazide, and in some experiments 2 QX-314. Electrode resistance was 3C8 M. Membrane voltage was amplified 50, low-pass filtered (4 kHz cutoff) having a Multiclamp 700B amplifier (Molecular Products), and digitized at 50 kHz with an ITC-18 data acquisition interface (Heka). For Ca2+ imaging experiments, 0.1 mm Oregon green BAPTA-1 (OGB1) was included in the pipette internal solution. An arbitrarily formed line crossing one or more dendritic segments was scanned with 920 nm laser light via high-speed Rgs5 galvometers (Prairie Ultima). The line-scan period was 1.1C4.3 ms. During two-photon glutamate uncaging experiments, 8.33 mm MNI-glutamate in ACSF was pressure ejected from a glass pipette positioned at the surface of the slice above the uncaging location. Laser pulses (720 nm) of Moclobemide 0.2 ms duration were delivered at each of 13C25 sites within the distal dendrite of a WF cell with 0.2 ms between each pulse/site. No response was observed to laser pulses in the absence of MNI-glutamate. To express channelrhodopsin-2 (ChR2) in RGCs, we injected 1 l of AAV-2.1-syn-ChR2-GFP into each attention and brain slices were prepared 4C5 weeks later. ChR2 was triggered with 1 ms LED flashes (470 nm maximum emission) delivered through a 63 objective. Synaptic reactions were abolished after bath software of the Na+ channel blocker TTX (0.5 m) or a combination of the AMPA and NMDA receptor antagonists NBQX (10 m) and AP5 (50 m), respectively. To express ChR2 or ArchT in horizontal cells, we injected 20 nL of AAV-2.1-syn-ChR2C2a-GFP or AAV-2. 1-syn-ArchT-GFP into each of two sites bilaterally in the SC of Gad-Cre mice. Coordinates (in millimeters: anterior from lambda,.