Developmental changes in the expression of NMDA receptor subunits (NR1, NR2A, NR2B) in the cat visual cortex and the effects of dark rearing

Expression of ionotropic glutamate receptors in the retina of the rdta transgenic mouse

BACKGROUND

The expression of retinal CaMKII is up-regulated in the retina of the rdta mouse in which rod photoreceptors are genetically ablated. As ionotropic glutamate receptors are known substrates of CAMKII, this study set out to determine if the protein levels of ionotropic glutamate receptors in the rdta mouse retina are also affected.

RESULTS

The NMDA receptor subunits (NR1, NR2A/B) and the GluR1; AMPA receptor subunit (GluR1) were examined in immunolabeled western blots. The results demonstrate that the amounts of NR1 and NR2A/B receptor subunits are significantly increased in crude synaptic membrane fractions isolated from retinae of the rdta mice when compared to their normal, littermate controls. The GluR1 receptor subunit and its phosphorylation are simultaneously increased in retinae of the rdta mice.

CONCLUSIONS

These data indicate that the NMDA receptors and AMPA (GluR1) receptors are altered in the retinae of rdta mice that lack rod photoreceptors. Because the rods are lost at an early stage in development, it is likely that these results are indicative of synaptic reorganization in the retina.

Developmental changes in the expression of GABA(A) receptor subunits (alpha(1), alpha(2), alpha(3)) in the cat visual cortex and the effects of dark rearing

The present study used Western blots and Northern slot blots to determine changes in the level of expression of GABA(A) receptor subunits alpha(1), alpha(2), and alpha(3), in relation to the "critical period" in cat visual cortex. Levels of the GABA(A) alpha(1) subunit were lowest at 1 week, increased four-fold to a maximum at 10 weeks, and declined slightly (35%) into adulthood. Levels of the GABA(A) alpha(2) and alpha(3) subunits were highest at 1 week of age, decreased two-fold by 10 weeks of age and were constant thereafter. Comparison between visual cortex from normal and dark-reared cats at 5 weeks and 20 weeks showed that alpha(1) and alpha(3) subunit expression was elevated in dark-reared animals by approximately 50% at both ages. alpha(2) expression was not affected. These results implicate the importance of a shift from putative immature to mature GABA(A) receptor subunits during the critical period of visual cortex and in conjunction with parallel analysis of NMDA receptor subunit maturation, further support the notion that a changing excitatory/inhibitory balance is critical for neuronal plasticity.