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Vision Res. 2016 Feb;119:99-109. doi: 10.1016/j.visres.2015.11.006. Epub 2016 Feb 5.

Connexin 36 and rod bipolar cell independent rod pathways drive retinal ganglion cells and optokinetic reflexes.

Author information

1
Department of Neuroscience, Baylor College of Medicine, Houston, TX, United States; Department of Ophthalmology, Baylor College of Medicine, Houston, TX, United States. Electronic address: Cameron.Cowan@gmail.com.
2
Department of Neuroscience, Baylor College of Medicine, Houston, TX, United States.
3
Department of Ophthalmology, Baylor College of Medicine, Houston, TX, United States.
4
Department of Neurobiology, Harvard University, Boston, MA, United States.
5
Department of Medical Education, Paul L. Foster School of Medicine-TTUHSC, El Paso, TX, United States.
6
Department of Ophthalmology, Tufts University School of Medicine, Boston, MA, United States.
7
Department of Neuroscience, Baylor College of Medicine, Houston, TX, United States; Department of Ophthalmology, Baylor College of Medicine, Houston, TX, United States.

Abstract

Rod pathways are a parallel set of synaptic connections which enable night vision by relaying and processing rod photoreceptor light responses. We use dim light stimuli to isolate rod pathway contributions to downstream light responses then characterize these contributions in knockout mice lacking rod transducin-α (Trα), or certain pathway components associated with subsets of rod pathways. These comparisons reveal that rod pathway driven light sensitivity in retinal ganglion cells (RGCs) is entirely dependent on Trα, but partially independent of connexin 36 (Cx36) and rod bipolar cells. Pharmacological experiments show that rod pathway-driven and Cx36-independent RGC ON responses are also metabotropic glutamate receptor 6-dependent. To validate the RGC findings in awake, behaving animals we measured optokinetic reflexes (OKRs), which are sensitive to changes in ON pathways. Scotopic OKR contrast sensitivity was lost in Trα(-/-) mice, but indistinguishable from controls in Cx36(-/-) and rod bipolar cell knockout mice. Mesopic OKRs were also altered in mutant mice: Trα(-/-) mice had decreased spatial acuity, rod BC knockouts had decreased sensitivity, and Cx36(-/-) mice had increased sensitivity. These results provide compelling evidence against the complete Cx36 or rod BC dependence of night vision's ON component. Further, the findings suggest the parallel nature of rod pathways provides considerable redundancy to scotopic light sensitivity but distinct contributions to mesopic responses through complicated interactions with cone pathways.

KEYWORDS:

Mouse retina; Night vision; Optokinetic reflex; Retinal ganglion cell; Rod information convergence and segregation; Rod pathway

PMID:
26718442
PMCID:
PMC5052632
DOI:
10.1016/j.visres.2015.11.006
[Indexed for MEDLINE]
Free PMC Article

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