Likewise, during light adaptation,WTandPd/responses became even more comparable; there was no significant difference in the normalized amplitudes of dim flash responses in the presence of the background (p=0.44; black and gray thin traces,Fig. an additional synaptic phenotype in these experiments suggests that the function of phosducin at the photoreceptor synapse is usually abolished by the conditions of retinal slice recordings. == Introduction == Phosducin is one of the most highly expressed proteins in photoreceptors, yet its specific function in rods and cones has remained elusive. In its dephosphorylated state, phosducin binds to subunits of GDC0994 (Ravoxertinib) heterotrimeric G-proteins[1][4], which led to the hypothesis that phosducin adjusts the gain of phototransduction by dynamically reducing the amount of G-protein available to be activated GDC0994 (Ravoxertinib) during light adaptation. However, suction electrode recordings from rod outer segments lacking phosducin (Pd/) showed no detectable deficits in light adaptation[5]. Instead, rods were less sensitive and showed reduced amplification, owing to a small reduction in G-protein expression levels that was a secondary consequence of the loss of phosducin[5]. Phosducin is CKS1B usually expressed not only in the outer segments of photoreceptors but also the inner segments and synaptic terminals[6][9]. These observations prompted Herrmann et al.[10]to use the electroretinogram (ERG) b-wave to estimate the responses of dark- and light-adapted On-bipolar cells in wild-type (WT) andPd/mice. After taking into account the aforementioned decrease in sensitivity ofPd/rod outer segments[5], the b-wave intensity-response functions ofPd/mice were shifted by a factor of 2.7 toward brighter intensities, and exhibited less desensitization in steady light, than those ofWTmice. These differences were observed in both rod and cone pathways and attributed to the effects of phosducin at the synaptic terminal of photoreceptors[10]. Rods release glutamate not only onto rod bipolar cells (RBCs), but also onto subsets of On- and Off- cone bipolar cells, and are electrically coupled to cones that do likewise[11]. To evaluate the functional consequences of loss of phosducin specifically at the rod-to RBC synapse, we used single cell recordings to measure light-evoked currents from RBCs in acute retinal slices ofWTandPd/mice under both dark- and light-adapted conditions. Surprisingly, the intensity-response functions GDC0994 (Ravoxertinib) of thePd/RBCs were not right-shifted compared GDC0994 (Ravoxertinib) to those ofWTRBCs, but instead were slightly more nonlinear (steeper). In addition, the dim-flash responses ofPd/RBCs were significantly delayed relative to those ofWTRBCs, and showed less amplitude reduction in the presence of steady light. These results are consistent with reducedPd/rod sensitivity and a non-linear threshold for transmission at rod-to-RBC synapse in retinal slices, but not consistent with previous in vivo ERG results. == Materials and Methods == == Ethics statement == Mice in this study were cared for and handled according to procedures specifically approved by the Institutional Animal Care and Use Committee at the University of California at Davis and in strict accordance with the recommendations in the Guide for the Care and Use of Laboratory Animals of the National Institutes of Health. == Animals == All mice were bred and reared in 12-hour cyclic light. In some experiments, c57Bl/6 andPd/mice[9]were bred to generatePd+/mice that were subsequently bred in order to generatePd/andWTlittermate controls. There were no differences in the RBC properties ofWTlittermate controls and c57Bl/6 mice obtained commercially (Charles River), nor in thePd/RBCs of outbred or inbred strains (data not shown). == Retinal dissection and sectioning == Adult mice (36 weeks of age) were dark-adapted overnight, killed by cervical dislocation and decapitation, and the retinas removed under infrared light. Retinas were stored.