Axonal stratification patterns and glutamate‐gated conductance mechanisms in zebrafish retinal bipolar cells

Abstract

Retinal bipolar cells are physiologically separated into ON_ and OFF_subtypes based on responses to light andÏor glutamate, the photoreceptor neurotransmitter. OFF_bipolar cells are depolarized by glutamate release in the dark. ON_bipolar cells, in contrast, are hyperpolarized by the very same glutamate release. The division of the light signal into ON_ and OFF_pathways is achieved through a variety of glutamate receptors mediating these responses. OFFbipolar cells express ionotropic glutamate receptors (iGluRs) that are directly activated by glutamate or the glutamate agonists, kainate and á_amino-3-hydroxy-5-methylisoxazole-4-propionic acid (AMPA). Glutamate responses restricted to the kainate receptor family were recently described in OFF_bipolar cells of ground squirrel (DeVries & Schwartz, 1999). Kainate receptor currents are typically characterized by slower desensitization and recovery than AMPA receptor currents. Glutamate responses of the N-methyl-ª_aspartate (NMDA) family are not seen in retinal bipolar cells.Journal of Physiology (2000)

Zebrafish: A model system for the study of eye genetics

“…Amacrine cells were categorized into seven morphological subtypes, and though these morphological classifications are in basic agreement with previous reports using immunolabelling and metabolic signatures, a greater diversity of the amacrine cell subtypes will likely be identified using additional methods (Marc and Cameron, 2001;Yazulla and Studholme, 2001). Bipolar cells have been best characterized in zebrafish using a combination of physiological recordings followed by backfilling with a fluorescent dye or DiOlistic labeling (Connaughton and Nelson, 2000). The majority of the bipolar cells demonstrate ON or OFF responses consistent with their terminals being in sublamina b of the inner plexiform layer or sublamina a respectively.…”

Regulation of ON bipolar cell activity

“…Subsequent studies revealed that the synaptic response generated by the cone pathway is probably not a true glutamate receptor, but instead displays a transporter-like pharmacology. Most likely the transported ion is Cl − Dowling, 1995, 1996;Connaughton and Nelson, 2000). However, by activating a Cl-conductance, glutamate released from cones in the teleost still obeys the general rule that photoreceptor transmitter inhibits ON bipolar cells.…”

Human retinal circuitry and physiology.

“…Conedriven BC axon terminals stratify roughly at one of the two main sublaminas, whereas some present, in addition, characteristic patterns of multilaminar spread of terminals in the IPL (Mariani, 1983). BCs with terminations in both sublaminas of the IPL were also identified in a number of other species (Connaughton & Nelson, 2000;Scholes, 1975;Scholes & Morris, 1973;Wu, Gao, & Maple, 2000), but their response properties have not been thoroughly investigated.…”