Activity-dependent regulation of NMDA receptors (NMDARs) is a key feature in synaptic plasticity. In the olfactory bulb (OB) NMDARs are postsynaptically expressed on mitral cell dendrites receiving excitatory afferents from peripheral olfactory neurons, and on granule cells making dendro-dendritic contacts with mitral cells. NMDARs are hetero-oligomeric proteins formed by NR1 subunits, different NMDAR 2 subunits (NR2A-D) and possibly NR3 subunits. The NR1 gene encodes at least eight functional variants by alternative splicing of exon 5 (cassette N1), 21 (cassette C1), or 22 (cassettes C2 or C2'). In the present work we tested the possibility that the primary afferents regulate NMDA receptor subunit expression and alternative splicing in the OB. To this aim we analyzed the expression levels of NR1 and NR2A-D subunits 2, 8, 14, 21, 44, 65 and 100 days after OB peripheral denervation by zinc sulfate intranasal irrigation. Taking advantage of the laminar organization of the OB, we microdissected each layer and processed it for quantitative RT-PCR. Western blot and immunohistochemical analysis were performed to study protein changes. Between the NR2 subunits, NR2D showed the highest change in mRNA expression, which is significantly downregulated starting from 8 days post lesion (dpl) in the glomerular layer. The most evident effect was found in the mitral cell layer where N1-lacking NR1 subunits were transiently upregulated early after deafferentation to go back to normal levels by 21 dpl. In contrast, N1-containing subunits decreased their expression starting from 8 dpl up to100 dpl. The ratio between N1 lacking/N1-containing transcripts changed from 1.2 (control) to 2.3 (14 dpl) to 1.9 (100 dpl). Similar changes were observed in the granule cell layer. These results imply that in the OB sensory activity is able to regulate the N1 cassette splicing of the NR1 subunit.
Primary afferents regulate NMDA expression in the adult olfactory bulb
BOVOLIN, Patrizia;BOVETTI, Serena;FASOLO, Aldo;
2005-01-01
Abstract
Activity-dependent regulation of NMDA receptors (NMDARs) is a key feature in synaptic plasticity. In the olfactory bulb (OB) NMDARs are postsynaptically expressed on mitral cell dendrites receiving excitatory afferents from peripheral olfactory neurons, and on granule cells making dendro-dendritic contacts with mitral cells. NMDARs are hetero-oligomeric proteins formed by NR1 subunits, different NMDAR 2 subunits (NR2A-D) and possibly NR3 subunits. The NR1 gene encodes at least eight functional variants by alternative splicing of exon 5 (cassette N1), 21 (cassette C1), or 22 (cassettes C2 or C2'). In the present work we tested the possibility that the primary afferents regulate NMDA receptor subunit expression and alternative splicing in the OB. To this aim we analyzed the expression levels of NR1 and NR2A-D subunits 2, 8, 14, 21, 44, 65 and 100 days after OB peripheral denervation by zinc sulfate intranasal irrigation. Taking advantage of the laminar organization of the OB, we microdissected each layer and processed it for quantitative RT-PCR. Western blot and immunohistochemical analysis were performed to study protein changes. Between the NR2 subunits, NR2D showed the highest change in mRNA expression, which is significantly downregulated starting from 8 days post lesion (dpl) in the glomerular layer. The most evident effect was found in the mitral cell layer where N1-lacking NR1 subunits were transiently upregulated early after deafferentation to go back to normal levels by 21 dpl. In contrast, N1-containing subunits decreased their expression starting from 8 dpl up to100 dpl. The ratio between N1 lacking/N1-containing transcripts changed from 1.2 (control) to 2.3 (14 dpl) to 1.9 (100 dpl). Similar changes were observed in the granule cell layer. These results imply that in the OB sensory activity is able to regulate the N1 cassette splicing of the NR1 subunit.
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