GABAA and GABAC receptor antagonists increase retinal cyclic GMP levels through nitric oxide synthase

Dou Yu, William D. Eldred*

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

11 Scopus citations

Abstract

The nitric oxide (NO)/cyclic guanosine monophosphate (cGMP) signal transduction pathway plays a role in every retinal cell type, Previous studies have shown that excitatory glutamatergic synaptic pathways can increase cGMP-like immunoreactivity (cGMP-LI) in retina through stimulation of NO production, but little is known about the role of synaptic inhibition in the modulation of cGMP-LI, Gamma-amino-n-butyric acid (GABA) plays critical roles in modulating excitatory synaptic pathways in the retina. Therefore, we used GABA receptor antagonists to explore the role of GABAergic inhibitory synaptic pathways on the modulation of the NO/cGMP signal-transduction system. Cyclic GMP immunocytochemistry was used to investigate the effects of the GABA receptor antagonists bicuculline, picrotoxin, and (1,2,5,6- tetrahyropyridin-4-yl) methylphosphinic acid (TPMPA) on levels of cGMP-LI. Cyclic GMP-LI was strongly increased in response to the GABAA receptor antagonist bicuculline, while the GABAC receptor antagonist TPMPA had little effect on cGMP-LI. The GABAA/GABAC receptor antagonist, picrotoxin, caused a moderate increase in cGMP-LI, which was mimicked by the combination of bicuculline and TPMPA. The nitric oxide synthase inhibitor, S-methyl-L-thiocitrulline (SMTC), blocked the increased cGMP-LI in response to stimulation with either bicuculline or picrotoxin. Treatments with either of the glutamate receptor antagonists (5R,10S) -(+)-5-methyl-10,11-dihydro-5H-dibenzo[a,d]cyclohepten-5,10-imine (MK-801) or 6-cyano-7-nitroquinoxaline-2,3-dione (CNQX) partially blocked the increases in cGMP-LI seen in response to bicuculline, but a combination of MK-801 and CNQX completely eliminated these increases. These results suggest that inhibitory synaptic pathways involving both types of GABA receptors work through excitatory glutamatergic receptors to regulate the NO/cGMP signal- transduction pathway in retina.

Original languageEnglish (US)
Pages (from-to)627-637
Number of pages11
JournalVisual Neuroscience
Volume20
Issue number6
DOIs
StatePublished - Nov 2003

Keywords

  • Amacrine cell
  • Bipolar cell
  • GABA receptors
  • Immunocytochemistry
  • Nitric oxide
  • Retina
  • Turtle
  • cGMP

ASJC Scopus subject areas

  • Physiology
  • Sensory Systems

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