Adenosine A(2A) receptor up-regulates retinal wave frequency via starburst amacrine cells in the developing rat retina.
BACKGROUND
Developing retinas display retinal waves, the patterned spontaneous activity essential for circuit refinement. During the first postnatal week in rodents, retinal waves are mediated by synaptic transmission between starburst amacrine cells (SACs) and retinal ganglion cells (RGCs). The neuromodulator adenosine is essential for the generation of retinal waves. However, the cellular basis underlying adenosine's regulation of retinal waves remains elusive. Here, we investigated whether and how the adenosine A(2A) receptor (A(2A)R) regulates retinal waves and whether A(2A)R regulation of retinal waves acts via presynaptic SACs.


RESULTS
We showed that A(2A)R was expressed in the inner plexiform layer and ganglion cell layer of the developing rat retina. Knockdown of A(2A)R decreased the frequency of spontaneous Ca²⁺ transients, suggesting that endogenous A(2A)R may up-regulate wave frequency. To investigate whether A(2A)R acts via presynaptic SACs, we targeted gene expression to SACs by the metabotropic glutamate receptor type II promoter. Ca²⁺ transient frequency was increased by expressing wild-type A(2A)R (A2AR-WT) in SACs, suggesting that A(2A)R may up-regulate retinal waves via presynaptic SACs. Subsequent patch-clamp recordings on RGCs revealed that presynaptic A(2A)R-WT increased the frequency of wave-associated postsynaptic currents (PSCs) or depolarizations compared to the control, without changing the RGC's excitability, membrane potentials, or PSC charge. These findings suggest that presynaptic A(2A)R may not affect the membrane properties of postsynaptic RGCs. In contrast, by expressing the C-terminal truncated A(2A)R mutant (A(2A)R-ΔC) in SACs, the wave frequency was reduced compared to the A(2A)R-WT, but was similar to the control, suggesting that the full-length A(2A)R in SACs is required for A(2A)R up-regulation of retinal waves.


CONCLUSIONS
A(2A)R up-regulates the frequency of retinal waves via presynaptic SACs, requiring its full-length protein structure. Thus, by coupling with the downstream intracellular signaling, A(2A)R may have a great capacity to modulate patterned spontaneous activity during neural circuit refinement.
Institute of Molecular and Cellular Biology, National Taiwan University, Taipei, Taiwan.
Pin-Chien
PC
Huang
Institute of Molecular and Cellular Biology, National Taiwan University, Taipei, Taiwan.
Yu-Tien
YT
Hsiao
Institute of Molecular and Cellular Biology, National Taiwan University, Taipei, Taiwan; Department of Life Science, National Taiwan University, Taipei, Taiwan.
Shao-Yen
SY
Kao
Institute of Molecular and Cellular Biology, National Taiwan University, Taipei, Taiwan.
Ching-Feng
CF
Chen
Institute of Molecular and Cellular Biology, National Taiwan University, Taipei, Taiwan; Department of Life Science, National Taiwan University, Taipei, Taiwan.
Yu-Chieh
YC
Chen
Institute of Molecular and Cellular Biology, National Taiwan University, Taipei, Taiwan; Department of Life Science, National Taiwan University, Taipei, Taiwan.
Chung-Wei
CW
Chiang
Institute of Biomedical Sciences, Academia Sinica, Taipei, Taiwan.
Chien-Fei
CF
Lee
Department of Physiology and Pharmacology, College of Medicine, Chang Gung University, Tao-Yuan, Taiwan.
Juu-Chin
JC
Lu
Institute of Biomedical Sciences, Academia Sinica, Taipei, Taiwan.
Yijuang
Y
Chern
Institute of Molecular and Cellular Biology, National Taiwan University, Taipei, Taiwan; Department of Life Science, National Taiwan University, Taipei, Taiwan; Neurobiology and Cognitive Science Center, National Taiwan University, Taipei, Taiwan; Genome and Systems Biology Degree Program, National Taiwan University, Taipei, Taiwan.
Chih-Tien
CT
Wang
D000200:Action Potentials; D000262:Adenylyl Cyclases / Q000378:metabolism; D025042:Amacrine Cells / Q000166:cytology*; D000818:Animals; D002118:Calcium / Q000378:metabolism; D000242:Cyclic AMP / Q000378:metabolism; D018507:Gene Expression Regulation, Developmental; D055785:Gene Knockdown Techniques; D057054:Molecular Imaging; D009154:Mutation; D051381:Rats; D043705:Receptor, Adenosine A2A / Q000737:chemistry / Q000172:deficiency / Q000235:genetics / Q000378:metabolism*; D012160:Retina / Q000166:cytology* / Q000254:growth & development*; D012165:Retinal Ganglion Cells / Q000166:cytology / Q000378:metabolism; D015398:Signal Transduction; D055366:Synaptic Potentials; D015854:Up-Regulation
D043705:Receptor, Adenosine A2A; D000242:Cyclic AMP; D000262:Adenylyl Cyclases; D002118:Calcium