To compare the importance of rebound depolarizations to those mediated by synaptic excitation, we recorded OFF RGC responses to somatic current injections (see Figure S1 available online). Even for current steps PF-06463922 datasheet (−150 pA) that hyperpolarized OFF RGCs (−102.6 ± 8.3 mV, n = 7 cells) well below the likely reversal potential for inhibitory conductances at this age (Zhang et al., 2006), only two of seven cells fired rebound

spikes. Moreover, when observed, rebound firing gave rise to only few action potentials compared to the robust spike bursts elicited by depolarizing current injections (Figure S1) and observed during waves (Figures 1C and 1D). Responses of ON RGCs to current injections were similar to those of OFF RGCs (Figure S1). Thus, it appears that the offset bursts of ON and OFF RGCs are elicited by sequential excitatory inputs to these neurons, which in the case of ON RGCs outweigh simultaneous inhibitory inputs and in the case of OFF RGCs are preceded by inhibition. Several studies have shown that excitatory input to RGCs during stage III waves is mediated by glutamate and

recent reports identify BCs as its likely source (Blankenship et al., 2009, Firl et al., 2013 and Wong et al., 2000). selleck kinase inhibitor However, how BCs themselves respond during waves is not well understood. To address this question and elucidate the mechanisms that offset excitatory inputs to ON and OFF RGCs, we obtained dual whole-cell patch-clamp recordings from BCs and RGCs

with overlapping neurite territories in P11–P13 retinal flat mount preparations (Figures 2A and 2B). The dendrites of BCs contact either rod (RBCs) or cone (CBCs) photoreceptors. All CBCs (43/43 cells) but no RBCs (0/4 cells) we recorded participated in stage III waves. Like RGCs, CBCs can be grouped into ON and OFF classes. over The axons of ON CBCs stratify in the inner 3/5 of the IPL, those of OFF CBCs in the outer 2/5 where they contact the dendrites of ON and OFF RGCs, respectively (Ghosh et al., 2004). Simultaneous recordings of ON CBCs and ON RGCs revealed that during each stage III wave, ON CBCs depolarize while their membrane potential remains relatively stable between waves (Figure 2C; VRest: −59.4 ± 1.6 mV, n = 27). The timing and shape of ON CBC depolarizations matched those of concurrently recorded ON RGC EPSCs (Figures 2D and 2E; PT: 56 ± 43 ms, n = 18). In contrast, OFF CBCs hyperpolarize during each stage III wave and rest at higher membrane potentials in between (Figure 2F; VRest: −48.4 ± 2.4 mV, n = 16 cells, p < 10−3 for comparison to ON CBCs). The timing of the respective events, similar to depolarizations of ON CBCs, was aligned with the ON phase of each wave (Figure 2G; trough time of cross-correlation: 52 ± 194 ms, n = 10).