Agonist‐stimulated cobalt uptake provides selective visualization of neurons expressing AMPA‐ or kainate‐type glutamate receptors in the retina

Abstract

Fast-acting excitatory neurotransmission in the retina is mediated primarily by glutamate, acting at alpha-amino-3-hydroxy-5-methyl-4-isoxazole propionic acid (AMPA) -selective and kainate-selective receptors. To localize these sites of action, cat retinas were stimulated with either AMPA or kainate and processed for histochemical visualization of cobalt uptake through calcium-permeable channels. Treatment with both agonists resulted in staining of A- and B-type horizontal cells and several types of OFF cone bipolar cells; there was no evidence for staining of ON cone bipolar cells or rod bipolar cells. The subpopulations of OFF cone bipolar cells differed in their responses with two distinct types that stained heavily with cobalt after exposure to AMPA and three different types that were preferentially labeled after exposure to kainate. Although many amacrine and ganglion cells appeared to respond to both agonists, AII amacrine cells were stained after stimulation by AMPA but not by kainate. The OFF cone bipolar cells that exhibit AMPA-stimulated cobalt uptake were found to have a high level of correspondence with cells that show immunocytochemical staining for the AMPA-selective glutamate receptor subunits GluR1 and GluR2/3. Similarly, the cone bipolar cells exhibiting kainate-stimulated cobalt uptake resemble those that are immunoreactive for the kainate subunit GluR5. The results indicate that, whereas many retinal neurons express both AMPA and kainate receptors, AII amacrine cells and subpopulations of OFF cone bipolar cells are limited to the expression of either AMPA or kainate receptors. This differential expression may contribute to the unique character of transmission by these cell types.

OFF midget bipolar cells in the retina of the marmoset, Callithrix jacchus, express AMPA receptors

“…Finally, the kainate receptor subunit GluR5 is not colocalized with the FMB dendrites or with the GluR1 subunit, indicating that a different bipolar cell type expresses this subunit. This result is consistent with findings in cat and ground squirrel retinas showing that AMPA and kainate receptors are expressed by distinct types of bipolar cells (DeVries, 2000;Pourcho et al, 2002;DeVries et al, 2006). Whether FMB cells also express the AMPA receptor subunits GluR2/3 and GluR4, which have been found at low numbers of flat contacts in cat, rodent, and macaque retinas Pourcho, 1996, 1999b;Morigiwa and Vardi, 1999;Hack et al, 2001;Haverkamp et al, 2001a), remains to be determined.…”

“…Consistently, Pourcho and coworkers (Qin and Pourcho, 1999a;Pourcho et al, 2002) suggested that, in cat retina, there are two types of OFF cone bipolar cell expressing AMPA receptors. On the other hand, in ground squirrel retina, to date, only one type of AMPA-receptor-expressing bipolar cell, the b2 cell, has been found (DeVries, 2000;DeVries et al, 2006).…”

“…It has been suggested that, in mammalian retinas, more than one type of OFF bipolar cell expresses kainate recep-tors (Marc, 1999;DeVries, 2000;Haverkamp et al, 2001b;Qin and Pourcho, 2001;Pourcho et al, 2002). In primate retina, the diffuse bipolar cell types DB1 and DB2 are the most likely candidates for the expression of the GluR5 subunit, because these cell types make the highest proportion of NTA contacts (Hopkins and Boycott, 1997).…”

Mapping glutamate responses in immunocytochemically identified neurons of the mouse retina

“…10C). Although the immunocytochemical procedures using DAB as the reaction product does not allow for colocalization with macromolecular markers, it does allow for a permanent reaction product, and hence long-term storage without photobleaching, similar to the cobalt uptake studies by Pourcho et al (2002). Figure 10D-H shows five small panels of individual hyperpolarizing bipolar cells that show KA-evoked AGB entry (panels inside black rectangular box).…”

“…An alternative method to understanding retinal circuitry has been to use the gating of organic or nonorganic cations to identify neurons that possess functional receptor channels (Pruss et al, 1991;Marc, 1999a,b;Michel, 2002, 2003;Marc and Jones, 2002;Pourcho et al, 2002;Marc et al, 2003;Sun et al, 2003). One of these approaches has been to use agmatine (1-amino-4-guanidobutane; AGB), a cationic guanidinium analog that permeates activated ionotropic glutamate receptor channels while not permeating other cation channels such as voltagegated Na ϩ and Ca 2ϩ channels or be taken up by Na ϩ coupled transporters (Marc, 1999a,b;Edwards and Michel, 2002;Sun et al, 2003;Kalloniatis et al, 2004).…”