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J. Chua, E. L. Fletcher, M. Kalloniatis; AMPA/Kainate Activates Depolarizing Cone Bipolar Cells in the rd1 Mouse Retina. Invest. Ophthalmol. Vis. Sci. 2007;48(13):1346.
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© ARVO (1962-2015); The Authors (2016-present)
Retinal remodeling such as altered expression of glutamate receptors have been found in Retinitis Pigmentosa. We investigated the functional characteristics of retinal neurons in the developing rd1 mice by mapping the permeability of glutamate gated channel, secondary to receptor activation using agmatine - AGB,
Retinal eyecups from rd1 mice were collected at different developmental ages: postnatal day 5 (P5; before rod degeneration), P15 (during peak of rod degeneration) and P25 (after rod degeneration). The retinae were incubated in physiological medium containing 25mM AGB, under basal conditions (no glutamate agonists), or with 30µM AMPA, 50µM KA or 1mM NMDA for 5 minutes. After incubation, the retinae were aldehyde fixed and processed for fluorescence immunocytochemistry. Cell-type specific antibodies (PKCα: labels rod bipolar cells; Islet-1: labels all depolarizing bipolar cells), and anti-AGB labelling were colocalized to determine cation channel permeation signals within identified cell classes.
In control retinae (C57/Bl6), there was a characteristic time of expression of functional glutamate receptors in the inner retina: functional AMPA/KA receptors were evident from embryonic day 18, whilst functional NMDA receptors appeared at ~P1 (Acosta, Chua and Kalloniatis, JCN in press). At P5 in the rd1 retina, NMDA activation appeared normal but activation of AMPA/KA was not evident. At P15 and P25, more bipolar cells were activated by AMPA/KA than in the control retina. To identify these bipolar cells, Islet-1 and PKCα were colocalized with AGB immunoreactivity secondary to AMPA or KA activation. The bipolar cells that showed AGB gating secondary to AMPA/KA activation included Islet-1 immunoreactive but not PKCα immunoreactive bipolar cells, indicating functional AMPA/KA receptors on cone depolarizing bipolar cells. Some bipolar cells activated by AMPA/KA did not colocalize with either Islet-1 or PKCα and are therefore hyperpolarizing cone bipolar cells.
There is a delay in the onset of functional AMPA/KA receptors in the inner retina of the rd1 mouse. In addition, the aberrant cation channel activation with AMPA/KA application suggests that the cone depolarizing bipolar cells are expressing functional AMPA/KA receptors in the degenerating rd1 retina.
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