title: Simultaneous contribution of two rod pathways to AII amacrine and cone bipolar cell light responses.
abstract: Rod signals traverse several synapses en route to cone bipolar cells. In one pathway, rods communicate directly with cones via gap junctions. In a second pathway, signals flow rods-rod bipolars-AII amacrines-cone bipolars. The relative contribution of each pathway to retinal function is not well understood. Here we have examined this question from the perspective of the AII amacrine. AIIs form bidirectional electrical synapses with on cone bipolars. Consequently, as on cone bipolars are activated by outer plexiform inputs, they too should contribute to the AII response. Rod bipolar inputs to AIIs were blocked by AMPA receptor antagonists, revealing a smaller, non-AMPA component of the light response. This small residual response did not reverse between -70 and +70 mV and was blocked by carbenoxolone, suggesting that the current arose in on cone bipolars and was transmitted to AIIs via gap junctions. The residual component was evident for stimuli 2 log units below cone threshold and was prolonged for bright stimuli, demonstrating that it was rod driven. Because the rod bipolar-AII pathway was blocked, the rod-driven residual current likely was generated via the rod-cone pathway activation of on cone bipolars. Thus for a large range of intensities, rod signals reach the inner retina by both rod bipolar-AII and rod-cone coupling pathways.
authors.affiliation: Department of Ophthalmology and Neuroscience, University of Texas Medical School, Houston, Texas, USA. brady.trexler@mssm.edu
authors.forename: E Brady
authors.initials: EB
authors.lastname: Trexler
authors.forename: Wei
authors.initials: W
authors.lastname: Li
authors.forename: Stephen C
authors.initials: SC
authors.lastname: Massey
mesh_terms: D025042:Amacrine Cells / Q000502:physiology* / Q000528:radiation effects; D000818:Animals; D001569:Benzodiazepines / Q000494:pharmacology; D001581:Benzothiadiazines / Q000494:pharmacology; D003952:Diagnostic Imaging / Q000379:methods; D004307:Dose-Response Relationship, Radiation; D004558:Electric Stimulation / Q000379:methods; D018691:Excitatory Amino Acid Antagonists / Q000494:pharmacology; D019706:Excitatory Postsynaptic Potentials / Q000502:physiology; D005260:Female; D019793:Fluorescein / Q000378:metabolism; D018756:GABA Antagonists / Q000494:pharmacology; D018684:Glycine Agents / Q000494:pharmacology; D066298:In Vitro Techniques; D008027:Light; D008297:Male; D008564:Membrane Potentials / Q000187:drug effects / Q000502:physiology / Q000528:radiation effects; D008954:Models, Biological; D009474:Neurons / Q000502:physiology / Q000528:radiation effects*; D018408:Patch-Clamp Techniques / Q000379:methods; D010852:Picrotoxin / Q000494:pharmacology; D011810:Quinoxalines / Q000494:pharmacology; D011817:Rabbits; D012160:Retina / Q000166:cytology / Q000502:physiology; D017948:Retinal Rod Photoreceptor Cells / Q000166:cytology* / Q000502:physiology; D013331:Strychnine / Q000494:pharmacology; D013569:Synapses / Q000502:physiology / Q000528:radiation effects; D009435:Synaptic Transmission / Q000528:radiation effects; D014795:Visual Pathways / Q000502:physiology / Q000528:radiation effects*
chemical_list: D001569:Benzodiazepines; D001581:Benzothiadiazines; D018691:Excitatory Amino Acid Antagonists; D019793:Fluorescein; D018756:GABA Antagonists; D018684:Glycine Agents; D010852:Picrotoxin; D011810:Quinoxalines; D013331:Strychnine; C062865:2,3-dioxo-6-nitro-7-sulfamoylbenzo(f)quinoxaline; C079692:GYKI 53655; C004639:cyclothiazide