G. Maguire et F. Werblin, DOPAMINE ENHANCES A GLUTAMATE-GATED IONIC CURRENT IN OFF BIPOLAR CELLS OF THE TIGER SALAMANDER RETINA, The Journal of neuroscience, 14(10), 1994, pp. 6094-6101
The transmitter glutamate is thought to be used by all vertebrate phot
oreceptors to drive the second-order neurons of the retina, horizontal
and bipolar neurons. Dopamine, an endogenous retinal neurotransmitter
localized to amacrine and interplexiform cells, has previously been s
hown to enhance glutamate-gated currents in retinal horizontal cells.
In the present study we demonstrate that bipolar cells, like horizonta
l cells, possess glutamate receptors that are modulated by dopamine. W
e then identify some components of the pathway through which dopamine
acts. We used whole-cell patch recording to measure how bath-applied d
opamine modulated the currents elicited by puffs of transmitter soluti
ons at bipolar cell dendrites. Excitatory amino acid-gated currents we
re evoked by pressure ejecting 1 mM glutamate or 10 mu M kainate for 4
0 msec through a micropipette positioned at the dendrites of bipolar c
ells. Bath-applied dopamine (20 mu M) enhanced the response to glutama
te in OFF bipolar cells in the retinal slice by 40% and in isolated OF
F bipolar cells by 65%. We also explored the components of the intrace
llular pathway mediating this modulation. Response enhancement was blo
cked by the D1 receptor antagonist SCH23390, but not by the D2 recepto
r antagonist spiperone, suggesting that the enhancement by dopamine is
mediated by a D1 receptor. GDP-beta-S, a G-protein inactivator, block
ed the enhancing action of dopamine, suggesting that the D1 receptor a
ctivated a G-protein to enhance the glutamate-gated current. Both 8-(4
-chloropenylthio)adenosine, a cAMP analog, and the addition of the cat
alytic subunit of protein kinase A (PKA) to the recording pipette enha
nced glutamate-gated currents, while H-7, a PK inactivator, and PKI(20
)amide, a PKA-specific inhibitor, blocked the enhancing action of dopa
mine. These data suggest that dopamine acts at D1 receptors in the den
drites of bipolar cells to activate adenyl cyclase, which through cAMP
enhances a glutamate-gated current in bipolar cell dendrites. Thus, d
opamine may modulate synaptic transmission from photoreceptors to OFF
bipolar cells.