Parvalbumin-expressing interneurons linearly control olfactory bulb output.

See Supplemental Information for additional procedures.

Animals

All procedures were in accordance with protocols approved by the UCSD Institutional Animal Care and Use Committee and guidelines of the National Institute of Health. Mice were acquired from Jackson Laboratories ( PV-Cre (Jax: 008069), Rosa-LSL-tdTomato (Jax: 007908)), GENSAT ( Pcdh21-Cre ) and Charles River (C57BL/6 wild-type) and group housed in disposable plastic cages with standard bedding in a room with a reversed light cycle (12h-12h). Experiments were performed during the dark period.

Virus injections Cre-dependent

AAV which expresses PSAM along with red fluorophore was created by replacing the GFP with nuclear-localizing dTomato (dTomNLS) in an AAV-syn-FLEX-PSAM L141F -GlyR-IRES-GFP plasmid ( Magnus et al., 2011 ) and packaged in an AAV2/1 serotype (AAV2/1-syn-FLEX-PSAM-IRES-dTomNLS) by UPenn Vector Core. AAV which drives GCaMP5G from the CaMKIIα promoter was created by placing the GCaMP5G gene after the 1.3 kb promoter region of the mouse CaMKIIα subunit gene and packaged into the AAV2/5 serotype (AAV2/5-CaMKII-GCaMP5G). Commercial vectors were purchased from UPenn Vector Core. GCaMP5G and PSAM expression was achieved by injecting viral solutions in the right olfactory bulb of adult mice at three locations (~500 μm apart), 20–40 nl at each site during window implantation. For PV cell GCaMP5G expression, AAV2/1-syn-FLEX-GCaMP5G was injected in the olfactory bulbs of PV-Cre homozygous mice. For granule cell GCaMP5G expression, a mixture of AAV2/1-syn-FLEX-GCaMP5G and AAV2/1-CMV-Cre (10:1) was injected in the granule cell layer of C57BL/6 mice. For mitral cell GCaMP5G expression, either AAV2/2-syn-GCaMP5G (custom vector from UPenn Vector Core) or AAV2/5-CaMKII-GCaMP5G was injected in PV-Cre mice or C57BL/6 mice. In two animals, AAV2/1-syn-FLEX-GCaMP5G was injected in Pcdh21-Cre mice, which drives Cre specifically in mitral/tufted cells. These three strategies for GCaMP5G expression in mitral cells gave similar results, verifying the use of Cre-independent vectors. For PSAM expression in PV cells, AAV2/1-syn-FLEX-PSAM-IRES-dTomNLS was injected in PV-Cre homozygous mice. Co-expression of GCaMP5G and PSAM was achieved by mixing the GCaMP5G and PSAM viral solutions at 1:1. ChR2 expression in PV cells was achieved by injecting AAV2/1-CAG-FLEX-ChR2-tdTomato in the olfactory bulb of P0-3 PV-Cre mice at 6 locations, 40–60 nl at each site. Coordinates, measured from the intersection of the midline and the inferior cerebral vein, were (anterior, lateral in μm): (100, 300), (100, 600), (400, 300), (400, 600), (700, 300) and (700, 600).

Slice electrophysiology

Patch-clamp recordings were performed using an upright microscope and DIC optics. Recordings were made using a Multiclamp 700A amplifier (Molecular Devices), digitized at 20 kHz, and acquired and analyzed using AxographX software. For most current and voltage-clamp recordings, pipettes (3–6 MΩ) contained (in mM): 150 Kgluconate, 1.5 MgCl 2 , 5 HEPES buffer, 0.1 EGTA 10 phosphocreatine, and 2.0 Mg-ATP [pH 7.4]. For measurements of the I–V relationship of PV cell EPSCs, a cesium-based internal solution was used (in mM): 130 D-gluconic acid, 130 CsOH, 5 NaCl, 10 HEPES, 10 EGTA, 12 phosphocreatine, 0.2 spermine, 3 Mg-ATP, and 0.2 Na-GTP [pH 7.3]. Series resistance was routinely