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Hung-Ya Tu, Yu-Jiun Chen, Chuan-Chin Chiao, Adam Rory McQuiston, Ching-Kang Jason Chen; Rhythmic membrane potential fluctuations of cholinergic amacrine cells in mice lacking ERG b-waves. Invest. Ophthalmol. Vis. Sci. 2015;56(7 ):3227.
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© ARVO (1962-2015); The Authors (2016-present)
Retinal ganglion cells (RGCs) in adult nob and Gb5-/- mice display spontaneous rhythmic spiking. It is undetermined whether membrane potential of amacrine cells undergoes similar fluctuations in these mice. We have recorded from genetically marked cholinergic starburst amacrine cells (SACs) and investigated possible underlying mechanisms.
SACs were genetically labeled by introducing the Ai9 mouse line into the ChAT-IRES-Cre knock-in background, which then bred into nob and Gb5-/- for patch clamp recordings. Whole-cell current and voltage clamp recordings were performed in flat-mounted retinas perfused with carbogenated mammalian Ringer solution. Pharmacological reagents were bath-applied and their effects on spontaneous rhythmic membrane potential fluctuations were calculated in OriginPro and presented as power spectra.
Both ON and OFF SAC in the inner nuclear layer of nob mice showed rhythmic depolarization with characteristic frequencies of 3.3 ± 0.68 Hz and 3.5 ± 0.58 Hz, respectively. Such fluctuations were blocked by combined AP5 (10 μM) and CNQX (10 μM), indicating that they were synaptically driven by upstream glutamatergic bipolar cells and not by cholinergic neighbors as tubocurarine (5 μM) had negligible effect. Sporadic inhibitory neurotransmission was noted in some SACs but was arrhythmic when it occurred, which could be diminished by combined PTX (50 μM) and TPMPA (10 μM) treatment but not by application of strychnine. Consistent with a contemporary model of RGC oscillations in mice with degenerated photoreceptors, we found that TTX (500 nM) and MFA (100 μM) treatment disrupted rhythms of fluctuation in both ON and OFF SACs. However, we found that dopamine (100 μM) treatment blocked only ON and not OFF SACs. Rhythmic membrane potential fluctuations in ON SACs could also be found in mice lacking Gb5 or in mice lacking RGS7 and RGS11, suggesting that it is a common phenomenon in mice lacking ERG b-waves.
We conclude that rhythmic fluctuations in SAC membrane potentials are secondary to the lack of ERG b-waves. Our data is also consistent with the notion that membrane potential oscillations of ON SACs involves the AII amacrine cell gap junction network. Because dopamine selectively blocks fluctuations in ON SACs but not those in OFF SACs, it appears that OFF SACs oscillation is driven by a different and unidentified mechanism.
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