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Y.-C. Chang, C.-Y. Chen, C.-C. Chiao; The Effect of Visual Experience on the Functional Expression of NMDA Receptors in the Developing Rabbit Retina. Invest. Ophthalmol. Vis. Sci. 2009;50(13):1413.
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Activation of NMDA glutamate receptors is critical for the initiation of synaptic plasticity. In the developing rat retina, the function of NMDA receptors has been associated with visual experience, though the light-dependent regulation of the subunit composition of NMDA receptors is lively debated (Xue and Cooper, 2001; Guenther et al., 2004). We characterized the functional expression of NMDA receptors in the developing rabbit retina, and examined the impact of light deprivation on regulation of the subunit composition of NMDA receptors.
The retinas from New Zealand White rabbits of different developmental stages (embryonic day 26, postnatal days 0 to 10, and adult) reared in normal or completely dark environments were isolated and cryosectioned into vertical slices. Antibodies against NR1 and NR2A/B were used to examine the neonatal expression patterns of NMDA receptor subunits. Functional NMDA receptors were further mapped by the agmatine (AGB) activation assay.
While the immunoreactivity of NR1 and NR2A/B subunits was detectable right after birth, our AGB activation assay showed that functional NMDA receptors can be identified as early as E26. The expression of NR1 was monotonically increased in both the IPL and the OPL throughout development, and no significant difference was observed between normal- and dark-reared animals. The expression of NR2A/B was present not only in the plexiform layers but also in the nuclear layers (INL and GCL) at birth, and no apparent difference between normal- and dark-reared animals was found. Furthermore, the AGB assay revealed that some amacrine and ganglion cells were activated with 100 uM NMDA from P0, and AGB signal of some horizontal and bipolar cells can be seen with increased concentration of NMDA (500 uM) from P6. Comparison of AGB permeation between normal- and dark-reared animals also showed no difference in functional expression of NMDA receptors.
Our results of functional expression of NMDA receptors in the early stages of the developing rabbit retina indicate that NMDA receptors participate in the synaptic maturation of the retinal circuits. Consistent with the electrophysiological study in the developing rat retina (Guenther et al., 2004), the regulation of the subunit composition of NMDA receptors is not light dependent in the developing rabbit retina.
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