Adenosine A(2A) receptor up-regulates retinal wave frequency via starburst amacrine cells in the developing rat retina

PLoS One. 2014 Apr 28;9(4):e95090. doi: 10.1371/journal.pone.0095090. eCollection 2014.

Abstract

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.

Methodology/principal findings: 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/significance: 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.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Action Potentials*
  • Adenylyl Cyclases / metabolism
  • Amacrine Cells / cytology*
  • Animals
  • Calcium / metabolism
  • Cyclic AMP / metabolism
  • Gene Expression Regulation, Developmental
  • Gene Knockdown Techniques
  • Molecular Imaging
  • Mutation
  • Rats
  • Receptor, Adenosine A2A / chemistry
  • Receptor, Adenosine A2A / deficiency
  • Receptor, Adenosine A2A / genetics
  • Receptor, Adenosine A2A / metabolism*
  • Retina / cytology*
  • Retina / growth & development*
  • Retinal Ganglion Cells / cytology
  • Retinal Ganglion Cells / metabolism
  • Signal Transduction
  • Synaptic Potentials
  • Up-Regulation*

Substances

  • Receptor, Adenosine A2A
  • Cyclic AMP
  • Adenylyl Cyclases
  • Calcium

Grants and funding

Funding was provided by Chang Gung Medical Research Project (CMRPD1C0591) and National Science Council (NSC-101-2320-B-182-007; NSC-102-2320-B-182-022-MY3) to JCL; National Science Council (NSC-100-2320-B-001-0110-MY3) to YC; National Taiwan University, National Science Council (NSC-97-2311-B-002-007-MY3; NSC-100-2321-B-002-001; NSC-100-2311-B-002-010) and National Health Research Institutes (NHRI-EX100-9718NC) to CTW. The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript.