The Journal of Neuroscience, November 1, 2001, 21(21):8624-8635
A Dopamine- and Protein Kinase A-Dependent Mechanism for Network
Adaptation in Retinal Ganglion Cells
Cecilia F.
Vaquero,
Angela
Pignatelli,
Gloria J.
Partida, and
Andrew T.
Ishida
Section of Neurobiology, Physiology, and Behavior,
University of California, Davis, California 95616
Vertebrates can detect light intensity changes in vastly different
photic environments, in part, because postreceptoral neurons undergo
"network adaptation." Previous data implicated dopaminergic, cAMP-dependent inhibition of retinal ganglion cells in this process yet
left unclear how this occurs and whether this occurs in darkness versus
light. To test for light- and dopamine-dependent changes in ganglion
cell cAMP levels in situ, we immunostained dark- and light-adapted retinas with anti-cAMP antisera in the presence and
absence of various dopamine receptor ligands. To test for direct
effects of dopamine receptor ligands and membrane-permeable protein
kinase ligands on ganglion cell excitability, we recorded spikes from
isolated ganglion cells in perforated-patch whole-cell mode before and
during application of these agents by microperfusion. Our
immunostainings show that light, endogenous dopamine, and exogenous
dopamine elevate ganglion cell cAMP levels in situ by activating D1-type dopamine receptors. Our spike recordings show that
D1-type agonists and 8-bromo cAMP reduce spike frequency and curtail
sustained spike firing and that these effects entail protein kinase A
activation. These effects resemble those of background light on
ganglion cell responses to light flashes. Network
adaptation could thus be produced, to some extent, by
dopaminergic modulation of ganglion cell spike generation, a mechanism
distinct from modulation of transmitter release onto ganglion cells or
of transmitter-gated currents in ganglion cells. Combining these
observations with results obtained in studies of photoreceptor,
bipolar, and horizontal cells indicates that all three layers of
neurons in the retina are equipped with mechanisms for adaptation to
ambient light intensity.
Key words:
retina; light adaptation; network adaptation; contrast
sensitivity; filtering; dopamine; protein kinase A
Copyright © 2001 Society for Neuroscience 0270-6474/01/21218624-12$05.00/0
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