Purchase this article with an account.
Matthew J. Van Hook, David M. Berson; Paired Recordings Of Dopaminergic Amacrines And ipRGCs. Invest. Ophthalmol. Vis. Sci. 2011;52(14):4553.
Download citation file:
© ARVO (1962-2015); The Authors (2016-present)
Intrinsically photosensitive retinal ganglion cells (ipRGCs) blend inhibitory and excitatory synaptic influences, with direct, melanopsin-based photoresponses. The resulting output signals feed non-image forming visual centers of the brain, and appear to influence the retina itself. Prior evidence suggests that M1-type ipRGCs interact bidirectionally with dopaminergic amacrine cells (DACs). Here, we asked whether DACs, which are thought to co-release GABA, are a source of GABAergic input onto ipRGCs and sought direct evidence for an ipRGC-to-DAC excitatory synapse.
To explore possible synaptic interactions between ipRGCs and DACs, we made paired whole-cell recordings in flat-mounted mouse retina from M1-type ipRGCs and DACs, which costratify in the outermost IPL. In order to target cells for recording, we interbred two existing mouse lines (TH::RFP and Opn4cre/+;Z/EG) so that the two cell types were labeled with distinct fluorophores. To test for synaptic interactions, we depolarized the presumptive presynaptic cell while voltage-clamping the postsynaptic cell to isolate excitatory or inhibitory post-synaptic currents.
We recorded from 19 M1 ipRGCs and DAC pairs. When ipRGCs were voltage-clamped at the cationic reversal potential, they typically exhibited spontaneous inhibitory post-synaptic currents (IPSCs). Depolarizing the DAC with either a step (n = 13 pairs) or using previously-recorded action potentials as a voltage-clamp command (n = 5 pairs) failed to evoke additional, time-locked IPSCs in the ipRGC. Likewise, we did not detect evoked post-synaptic currents when we used a high chloride concentration in the ipRGC recording pipette and voltage-clamped the cell to increase the Cl- driving force (n = 3). In one pair, step depolarization of the ipRGC evoked a train of excitatory post-synaptic currents (EPSCs) in a DAC that were blocked by the ionotropic glutamate receptor antagonist DNQX.
Although several pieces of evidence suggest that DACs are likely the source of GABA input onto M1-type ipRGCs, we were unable to evoke IPSCs in ipRGCs by stimulating DACs. This raises the possibility that DACs are not the source of GABA input. The presence of a glutamatergic synapse from ipRGCs to DACs is consistent with published reports.
This PDF is available to Subscribers Only