Reduced Retinal Function in the Absence of Na(v)1.6.

Area of Science:

• Neuroscience
• Vision Science
• Molecular Biology

Background:

• Scn8a gene encodes Na(v)1.6, a voltage-gated sodium channel (VGSC) vital for retinal neurons.
• Previous studies noted abnormal dark-adapted electroretinograms in Scn8a mutant mice.
• Light-adapted retinal function in these mutants remained uninvestigated.

Purpose of the Study:

• To investigate the role of Na(v)1.6 in light-adapted retinal function.
• To characterize electroretinogram (ERG) abnormalities in Scn8a mutant mice under light conditions.

Main Methods:

• Electoretinography (ERG) was performed on Scn8a mutant mice and control littermates under light-adapted conditions.
• Tetrodotoxin (TTX) was used to block VGSCs in control mice for comparison.
• Intravitreal injections of CoCl(2) or CNQX were used to isolate photoreceptor contributions to the ERG a-wave.

Main Results:

• Scn8a mutant mice exhibited significantly reduced a-wave and b-wave amplitudes during light adaptation.
• The reduction in ERG waves in mutants exceeded the effect of acute VGSC block by TTX in controls.
• Cone-isolated a-wave amplitude in mutants was comparable to controls at high luminance, suggesting normal cone photoreceptor function.

Conclusions:

• Scn8a mutant mice display reduced function in both rod and cone retinal pathways.
• The diminished b-wave suggests a post-photoreceptoral defect, potentially involving cone ON bipolar cells.
• Na(v)1.6 channels may play a significant role in augmenting signaling within cone bipolar cells.