Identification of a cone bipolar cell in cat retina which has input from both rod and cone photoreceptors

Abstract

It has been generally accepted that rod photoreceptor cells in the mammalian retina make synaptic contact with only a single population of rod bipolar cells, whereas cone photoreceptors contact a variety of cone bipolar cells. This assumption has been challenged in rodents by reports of a type of cone bipolar cell which receives input from both rods and cones. Questions remained as to whether similar pathways are present in other mammals. We have used an antiserum against the glutamate transporter GLT1-B to visualize a population of cone bipolar cells in the cat retina which make flat contacts with axon terminals of both rod and cone photoreceptor cells. These cells are identified as OFF-cone bipolar cells and correspond morphologically to type cb1 (CBa2) cone bipolar cells which are a major source of input to OFF-beta ganglion cells in the cat retina. The GLT1-B transporter was also localized to processes making flat contacts with photoreceptor terminals in rat and rabbit retinas. Examination of tissue processed for the GluR1 glutamate receptor subunit showed that cb1 cone bipolar cells, like their rodent counterparts, express this alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA)-selective receptor at their contacts with rod spherules. Thus, a direct excitatory pathway from rod photoreceptors to OFF-cone bipolar cells appears to be a common feature of mammalian retinas.

Type 4 OFF cone bipolar cells of the mouse retina express calsenilin and contact cones as well as rods

“…These findings argue for direct input from rods into the cone pathway referred to as the alternative rod pathway. In several species anatomical evidence for sparse synapse-like contacts from rods to OFF cone bipolar cells has been published (Hack et al, 1999Tsukamoto et al, 2001;Fyk-Kolodziej et al, 2003;Li et al, 2004, Mataruga et al, 2007. This connection could provide the anatomical basis for the alternative rod pathway.…”

“…One route signals through gap junctions between rod spherules and cone pedicles (DeVries and Baylor, 1995). In the other route, rods are directly connected with OFF cone bipolar cells (Soucy et al, 1998;Hack et al, 1999Hack et al, , 2001Tsukamoto et al, 2001;Fyk-Kolodziej et al, 2003;Li et al, 2004;Mataruga et al, 2007). However, the impact of this alternative pathway on transmission seems to be species dependent (Protti et al, 2005).…”

Synaptic Plasticity inCNGA3−/−Mice: Cone Bipolar Cells React on the Missing Cone Input and Form Ectopic Synapses with Rods

“…Direct rod to OFF cone bipolar cell connections have also been described in rat, cat, and rabbit retina (Hack et al, 1999;Fyk-Kolodziej et al, 2003;Li et al, 2004;Protti et al, 2005).…”

Convergence and Segregation of the Multiple Rod Pathways in Mammalian Retina

“…1C). Subsequent studies showed that rods make chemical synapses with OFF cone bipolar cells (Hack et al, 1999;Tsukamoto et al, 2001;Fyk-Kolodziej et al, 2003;Li et al, 2004). It is presently unclear whether rod-driven OFF signals use two or three distinct pathways.…”