TY - JOUR T1 - Alteration of AMPA receptor-mediated synaptic transmission by Alexa Fluor 488 and 594 in cerebellar stellate cells JF - eneuro JO - eneuro DO - 10.1523/ENEURO.0109-15.2016 SP - ENEURO.0109-15.2016 AU - Matthieu Maroteaux AU - Siqiong June Liu Y1 - 2016/05/25 UR - http://www.eneuro.org/content/early/2016/05/24/ENEURO.0109-15.2016.abstract N2 - The fluorescent dyes, Alexa Fluor 488 and 594 are commonly used to visualize dendritic structures and the localization of synapses, both of which are critical for the spatial and temporal integration of synaptic inputs. However the effect of the dyes on synaptic transmission is not known. Here we investigated whether Alexa dyes alter the properties of synaptic currents mediated by two subtypes of AMPA receptors (AMPARs) at cerebellar stellate cell synapses. In naïve mice, GluA2-lacking AMPAR mediated synaptic currents displayed an inwardly rectifying current-voltage (I-V) relationship due to blockade by cytoplasmic spermine at depolarized potentials. We found that inclusion of 100 µM Alexa dye, but not 10 µM, in the pipette solution led to a gradual increase in the amplitude of EPSCs at +40 mV and a change in the I-V relationship, from inwardly rectifying to more linear. In mice exposed to an acute stress, AMPARs switched to GluA2-containing receptors and 100 µM Alexa 594 did not alter the I-V relationship of synaptic currents. Therefore, a high concentration of Alexa dye changed the I-V relationship of EPSCs at GluA2-lacking AMPAR synapses.Significance Statement: Fluorescent dyes are commonly used to visualize dendritic structure in live neurons and to study the spatial and temporal integration of synaptic inputs. Here we report that a high concentration of the fluorescent dyes Alexa Fluor 594 and 488 altered AMPA receptor-mediated currents. Both dyes changed the current - voltage relationship of calcium permeable AMPA receptors that lack the GluA2 subunit and reduced the EPSC amplitude. Given that the current - voltage relationship is a commonly used method to determine AMPA receptor subunit composition, the use of Alexa dyes at high concentrations is not suitable when studying AMPA receptor-mediated synaptic transmission. ER -