the vesicular GABA transporter  or SNAP-25 , from horizontal cells. J: 10 m; F, L: 2.5 m. INL, internal nuclear layer; ONL, outer nuclear layer; OPL, outer plexiform layer.(PDF) pone.0083076.s001.pdf (465K) GUID:?75F2DA54-E733-437B-8F31-2A90B2A79027 Physique S2: Synaptic triads of rods and cones are intact in GluA4fl/fl:Cx57+/Cre. Electron micrographs of the outer plexiform layer of GluA4fl/fl (A, C) and GluA4fl/fl:Cx57+/Cre mice. Synaptic triads of rods (A, B) and cones (C, D) show no differences and contain lateral elements (asterisks), formed by horizontal cell dendrites, in Rabbit Polyclonal to GLRB both genotypes. Scale bar: 1 m.(PDF) pone.0083076.s002.pdf (317K) GUID:?88BFE378-549F-483E-93CA-5875E544051A Abstract In the mouse retina, horizontal cells form an electrically coupled network Dihydroethidium and provide feedback signals to photoreceptors and feedforward signals to bipolar cells. Thereby, horizontal cells contribute to gain control at the first visual synapse and to the antagonistic business of bipolar and ganglion cell receptive fields. However, the nature of horizontal cell output remains a matter of debate, just as the exact contribution of horizontal cells to center-surround antagonism. To facilitate studying horizontal cell function, we developed a knockin mouse line which allows ablating genes exclusively in horizontal cells. This knockin line expresses a Cre recombinase under the promoter of connexin57 (Cx57), a gap junction protein only expressed in horizontal cells. Consistently, in Cx57+/Cre mice, Cre recombinase is usually expressed in almost all horizontal cells (>99%) and no other retinal neurons. To test Cre activity, we crossbred Cx57+/Cre mice with a mouse line in which exon 11 of the coding sequence for the ionotropic glutamate receptor subunit GluA4 was flanked by two sites (GluA4fl/fl). In GluA4fl/fl:Cx57+/Cre mice, GluA4 immunoreactivity was significantly reduced (50%) in the outer retina where horizontal cells receive photoreceptor inputs, confirming the functionality of the Cre/system. Whole-cell patch-clamp recordings from isolated horizontal cell somata showed a reduction of glutamate-induced inward currents by 75%, suggesting that this GluA4 subunit plays a major role in mediating photoreceptor inputs. The persistent current in GluA4-deficient cells is mostly driven by AMPA and to a very small extent by kainate receptors as revealed by application of the AMPA receptor antagonist GYKI52466 and concanavalin A, a potentiator of kainate receptor-mediated currents. In summary, the Cx57+/Cre mouse line provides a versatile tool for studying horizontal cell function. GluA4fl/fl:Cx57+/Cre mice, in which horizontal cells receive less excitatory input, can thus be used to analyze the Dihydroethidium contribution of horizontal cells to retinal processing. Introduction Horizontal cells are interneurons in the mammalian retina which receive glutamatergic input from Dihydroethidium photoreceptors via ionotropic glutamate receptors . In turn, horizontal cells provide feedback and feedforward signals to photoreceptors and bipolar cells, respectively , allowing the retina to adjust to a broad range of light intensities. The mouse retina only contains a single type of horizontal cell – the Dihydroethidium axon-bearing B-type , which forms axo-axonal and dendro-dendritic networks coupled by the gap junction-forming protein connexin57 (Cx57) C. Although it is well known that horizontal cells play an important role in formation and maintenance of triad synapses with photoreceptors and bipolar cells  and in gain control of this synapse , many aspects of horizontal cell function remain elusive, e.g. the nature of the negative and positive feedback signals to rods and cones or the contribution of horizontal cells to ganglion cell receptive fields. Different techniques have been used to study horizontal cell function, including pharmacological approaches.