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Review
. 2015 Jul 5;370(1672):20140186.
doi: 10.1098/rstb.2014.0186.

Extrasynaptic release of GABA and dopamine by retinal dopaminergic neurons

Hajime Hirasawa  1 , Massimo Contini  2 , Elio Raviola  3
Affiliations
Review

Extrasynaptic release of GABA and dopamine by retinal dopaminergic neurons

Hajime Hirasawa et al. Philos Trans R Soc Lond B Biol Sci. .

Abstract

In the mouse retina, dopaminergic amacrine (DA) cells synthesize both dopamine and GABA. Both transmitters are released extrasynaptically and act on neighbouring and distant retinal neurons by volume transmission. In simultaneous recordings of dopamine and GABA release from isolated perikarya of DA cells, a proportion of the events of dopamine and GABA exocytosis were simultaneous, suggesting co-release. In addition, DA cells establish GABAergic synapses onto AII amacrine cells, the neurons that transfer rod bipolar signals to cone bipolars. GABAA but not dopamine receptors are clustered in the postsynaptic membrane. Therefore, dopamine, irrespective of its site of release-synaptic or extrasynaptic-exclusively acts by volume transmission. Dopamine is released upon illumination and sets the gain of retinal neurons for vision in bright light. The GABA released at DA cells' synapses probably prevents signals from the saturated rods from entering the cone pathway when the dark-adapted retina is exposed to bright illumination. The GABA released extrasynaptically by DA and other amacrine cells may set a 'GABAergic tone' in the inner plexiform layer and thus counteract the effects of a spillover of glutamate released at the bipolar cell synapses of adjacent OFF and ON strata, thus preserving segregation of signals between ON and OFF pathways.

Keywords: GABA; dopamine; extrasynaptic release; retina.

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Figures

Figure 1.
Figure 1.
Diagram of the distribution of the processes of the DA cell (red). OPL, outer plexiform layer; IPL, inner plexiform layer; a, sublamina OFF; b, sublamina ON.
Figure 2.
Figure 2.
A DA cell injected with neurobiotin was reconstructed from a montage of confocal images after treatment with a fluorescent antibody to the tracer. Only the cell body and the processes lying in stratum 1 of the inner plexiform layer are included in the figure. Dendrites and cell body are red, axons are black. The arrow points to the optic nerve head (from unpublished work in collaboration with B Lin and RH Masland).
See this image and copyright information in PMC

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