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AMPA receptor protein in developing rat brain: glutamate receptor-1 expression and localization change at regional,
L J Martin1, A Furuta, C D Blackstone
1Department of Pathology, Johns Hopkins University School of Medicine, Baltimore, MD 21205, USA.
Insights
Glutamate receptor 1 (GluR1) subunit expression and localization change during rat brain development. These developmental changes in GluR1 impact synaptic function and may influence brain vulnerability to injury.
Area of Science:
- Neuroscience
- Developmental Biology
- Molecular Biology
Background:
- The alpha-amino-3-hydroxy-5-methyl-4-isoxazole propionate (AMPA) receptor, specifically its GluR1 subunit, plays a critical role in synaptic plasticity and neurotransmission.
- Understanding the developmental regulation of GluR1 is crucial for comprehending brain maturation and its susceptibility to insults.
Purpose of the Study:
- To investigate the developmental changes in the regional, cellular, and synaptic localization of the GluR1 subunit in the rat brain.
- To determine how these changes correlate with brain maturation and synaptic development.
Main Methods:
- Immunoblotting to detect GluR1 levels in whole brain and specific regions during embryonic and postnatal development.
- Immunocytochemistry to visualize cellular expression patterns of GluR1 in different brain areas.
- Immunoelectron microscopy to examine the subcellular and synaptic localization of GluR1.
Main Results:
- GluR1 expression was detected early in embryonic development and increased postnatally, with distinct regional variations (increased in cortex, decreased in striatum).
- Cellular expression profiles varied, with transient expression in cerebellar neurons and progressive enrichment in neocortex and hippocampus.
- Synaptically, GluR1 was initially found in both pre- and postsynaptic sites, shifting to a somatodendritic localization in mature synapses.
Conclusions:
- GluR1 expression and localization are dynamically regulated throughout rat brain development.
- These developmental shifts in GluR1 distribution are linked to synaptic maturation.
- Altered GluR1 expression and localization in immature versus mature brains may underlie differential regional vulnerability to excitotoxicity and hypoxia-ischemia.
Abstract:
We tested the hypothesis that the regional, cellular, and synaptic localizations of the glutamate receptor 1 (GluR 1) subunit of the alpha-amino-3-hydroxy-5-methyl-4-isoxazole propionate receptor are regulated developmentally in rat brain. By immunoblotting, GluR1 was first detected in whole brain at embryonic day E15.5, and levels increased progressively during late embryonic (E20) and early postnatal (P2-P11) days. Regionally, GluR1 increased in cerebral cortex but decreased in striatum with postnatal maturation. These changes occurred in the presence of increased presynaptic maturation, as determined by synaptophysin detection. By immunocytochemistry, distinct cellular populations showed different temporal profiles of GluR1 expression during postnatal maturation. The neocortex and hippocampus showed a progressive maturation-related enrichment of GluR1, whereas the striatum showed a gradual reduction in GluR1 during maturation. In cerebellum, GluR1 protein was expressed transiently at restricted times postnatally by granule cells (P0-P11) and Purkinje cells (P13-P19), but by P21 and thereafter these neurons had sparse GluR1 immunoreactivity. By immunoelectron microscopy. GluR1 was found in neurites, specifically in both dendritic and axon terminal components of developing synapses. GluR1 was clustered at the plasma membrane of apparent growth cone appositions, neuronal cell bodies, and dendrites of developing neurons. The presence of GluR1 at presynaptic sites dissipated with synaptic maturation, as GluR1 became confined to the somatodendritic compartment as maturation progressed. We conclude that the regional expression as well as the cellular and synaptic localizations of the GluR1 are developmentally regulated and are different in immature and mature brain. Differences in glutamate receptor expression and synaptic localization in immature and mature brain may be relevant to the phenomenon that the perinatal and adult brain differ in their regional vulnerability to hypoxia-ischemia and excitotoxicity.