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Incorporation of the N-methyl-d-aspartate receptor (NMDAR) subunit NR3A into functional NMDARs results in reduced channel conductance and Ca(2+) permeability. To further investigate the function of NR3A, we have set out to characterize its intracellular binding partners. Here, we report a novel protein interaction between NR3A and microtubule associated-protein (MAP) 1B, which both are localized to dendritic shafts and filopodia. NR3A protein levels were increased in MAP1B deficient (-/-) mice, with a corresponding decrease in NR1 levels, but the fraction of filopodia immunoreactive for NR3A was equal in cells from -/- and wild type (WT) mice. NR3A has previously been shown to interact with another member of the MAP1 family, MAP1S. We showed that MAP1S binds to microtubules in a similar manner as MAP1B, and suggest that MAP1S and MAP1B both are involved in regulating trafficking of NR3A-containing NMDAR., (Copyright 2010 Elsevier Ireland Ltd. All rights reserved.)

Native N-methyl-D-aspartate (NMDA) receptors are heteromeric assemblies of four or five subunits. The NMDA receptor subunits, NR1, NR2A, NR2B, NR2C, and NR2D have been cloned in several species, including man. The NR3A subunit, which in rodents is predominantly expressed during early development, seems to function by reducing the NMDA receptor response. The human homologue to the rat NR3A, however, had not been cloned. In order to study the functions of the human NR3A (hNR3A), we have cloned and sequenced the hNR3A. It was found to share 88% of the DNA sequence with the rat gene, corresponding to a 93% homology at the amino acid level. Based on available data from human genome databases, we localized the gene to chromosome 9. The transcript could be detected by in situ hybridization in human fetal spinal cord and forebrain. Two splice variants of NR3A have been reported in rat brain, the longer of the two containing a 60 bp insert in the intracellular domain. We were unable to detect this 60 bp insert in fetal or adult human brain, suggesting that only the short variant is expressed in humans.

We studied the effects of the beta-amyloid (A beta) peptides A beta-(1-40), A beta-(25-35-NH2) and A beta-(25-35-COOH) on binding of the phosphoinositide derived, calcium mobilising, second messengers inositol(1,4,5)-trisphosphate (Ins(1,4,5)P3) and inositol(1,3,4,5)-tetrakisphosphate (Ins(1,3,4,5)P4) to their receptor sites in rat cerebral cortical membranes. All three peptides gave statistically significant dose-dependent increases in both [3H]Ins(1,4,5)P3 and [3H]Ins(1,3,4,5)P4 binding. A beta-(1-40) and A beta-(25-35-NH2) enhanced [3H]Ins(1,4,5)P3 and [3H]Ins(1,3,4,5)P4 binding to a similar extent. In comparison, A beta-(25-35-COOH) gave much greater enhancements of [3H]Ins(1,4,5)P3 and [3H]Ins(1,3,4,5)P4 binding. However, a component of the latter appeared to be due to the formation of pelletable A beta-(25-35-COOH)/[3H]Ins(1,3,4,5)P4 aggregates, that occurred in the absence of membranes. These results raise the possibility that A beta affects calcium homeostasis by a direct action on [3H]Ins(1,4,5)P3 and [3H]Ins(1,3,4,5)P4 receptor sites.

The effect of intraventricular administration of the neuropeptide galanin on acquisition and retrieval in a modified Morris swim maze was studied in rats. Galanin induced a significant deficit in the acquisition of the task while no effects on the retrieval were observed. No deficits were seen 24 h after the last treatment. Galanin did not increase the number of failures to reach the platform. It is suggested that endogenous galanin modulates learning possibly via the galanin-containing cholinergic neurons in the septum-basal forebrain area projecting to the hippocampus and cortex.