Retina Inside And Outside The Network Layer Structure, Function And Development

Lateral Components in the Cone Terminals of the Rabbit Retina:Horizontal Cell Origin and Glutamate Receptor ExpressionInstitute of Neuroscience, Chinese Academy of SciencesThe first synapse of the retina is a specialized stucture termed triad, it contains apresynaptic ribbon and three postsynaptic processes: two lateral components fromhoriontal cells (HCs) and one bipolar cell dentrite. Most mammalian retinas contain twotypes of HCs, dendrites of both types form lateral processes in cone terminals. Wesystematically studied the connections between cones and HCs and expression of AMPAand kainite receptors on HCs in cone pedicles of rabbit retinas using a combination ofintracellular injection, electron microscopy (EM) , immunohistochemical staining andconfocal microscopy. Our EM data showed that in each cone terminal, the proportion oflateral components originating from the A-and B-type HCs is about 50%;furtheranalysis of single triad revealed each of three possible combinations of HC processes (A-A, A-B, B-B) occurs at 33%. Immunohistochemical triple labelling showed that 55% ofA-type and 22% B-type terminal processes express GluR2/3;whereas, about 30% ofterminals of both HCs expressed GluR6/7. Our results indicate that each cone terminalconnects to an equal number of terminal processes originating from two types of HCs,however, the differential expression of receptors and permeability of gap junctions mayprovide two types of HCs to mediate feedback signals with different spatial and temporalcharacteristics.