KCC2-dependent subcellular ECl difference of ON-OFF retinal ganglion cells in larval zebrafish

Subcellular difference in the reversal potential of Cl- (E-Cl) has been found in many types of neurons. As local E-Cl largely determines the action of nearby GABAergic/glycinergic synapses, subcellular E-Cl difference can effectively regulate neuronal computation. The ON-OFF retinal ganglion cell (RGC) processes both ON and OFF visual signals via its ON and OFF dendrites, respectively. It is thus interesting to investigate whether the ON and OFF dendrites of single RGCs exhibit different local E-Cl. Here, using in vivo gramicidin-perforated patch recording in larval zebrafish ON-OFF RGCs, we examine local E-Cl at the ON and OFF dendrites, and soma through measuring light-evoked ON and OFF inhibitory responses, and GABA-induced response at the soma, respectively. We find there are subcellular E-Cl differences between the soma and dendrite, as well as between the ON and OFF dendrites of single RGCs. These somato-dendritic and inter-dendritic E-Cl differences are dependent on the Cl- extruder, K+/Cl- co-transporter (KCC2), because they are largely diminished by down-regulating kcc2 expression with morpholino oligonucleotides (MOs) or by blocking KCC2 function with furosemide. Thus, our findings indicate that there exists KCC2-dependent E-Cl difference between the ON and OFF dendrites of individual ON-OFF RGCs that may differentially affect visual processing in the ON and OFF pathways.