NMDA receptors are found in neurons both at synapses and in extrasynaptic locations. Extrasynaptic locations are poorly characterized. Here we used preembedding immunoperoxidase and postembedding immunogold electron microscopy and fluorescence light microscopy to characterize extrasynaptic NMDA receptor locations in dissociated hippocampal neurons in vitro and in the adult and postnatal hippocampus in vivo. We found that extrasynaptic NMDA receptors on neurons in vivo and in vitro were usually concentrated at points of contact with adjacent processes, which were mainly axons, axon terminals, or glia. Many of these contacts were shown to contain adhesion factors such as cadherin and catenin. We also found associations of extrasynaptic NMDA receptors with the MAGUKs, PSD-95 and SAP102. Developmental differences were also observed. At postnatal day 2 in vivo, extrasynaptic NMDA receptors could often be found at sites with distinct densities whereas dense material was seen only rarely at sites of extrasynaptic NMDA receptors in the adult hippocampus in vivo. This difference probably indicates that many sites of extrasynaptic NMDA receptors in early postnatal ages represent synapse formation or possibly sites for synapse elimination. At all ages, as suggested in both in vivo and in vitro studies, extrasynaptic NMDA receptors on dendrites or the sides of spines may form complexes with other proteins, in many cases, at stable associations with adjacent cell processes. These associations may facilitate unique functions for extrasynaptic NMDA receptors. KeywordsPSD-95; SAP102; cadherin; catenin; NR2A; NR2B Extrasynaptic NMDA receptors (NMDARs) are common on neurons but are little understood compared to synaptic NMDARs. In hippocampal neuronal cultures, physiological studies showed that ~ 75% of NMDARs are extrasynaptic at about 1 WIV (= week or weeks in vitro; Rosenmund et al., 1995; Westbrook, 1999, 2002) but this decreases with the published values ranging from ~ 20% to 50% at 2 WIV (Ivanov et al., 2006).Correspondence: Ronald S. Petralia 50 South Drive, Rm. 4142 NIDCD/NIH Bethesda, MD 20892-8027 301-496-3804 petralia@nidcd.nih.gov. Publisher's Disclaimer: This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final citable form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain. NIH Public Access Author ManuscriptNeuroscience. Author manuscript; available in PMC 2011 April 28. Published in final edited form as:Neuroscience. NIH-PA Author ManuscriptNIH-PA Author Manuscript NIH-PA Author ManuscriptImmunocytochemical studies indicate that about 80-90% of NMDARs are extrasynaptic at 1 WIV. These comprise both NR2A-and NR2B-containing receptors. At 1 WIV, the majority of N...

Background and Purpose-Blockade of angiotensin II AT 1 receptors in cerebral microvessels protects against brain ischemia and inflammation. In this study, we tried to clarify the presence and regulation of the local renin-angiotensin system (RAS) in brain microvessels in hypertension. Methods-Spontaneously hypertensive rats (SHR) and Wistar Kyoto (WKY) controls were treated with an AT 1 receptor antagonist (candesartan, 0.3 mg/kg per day) via subcutaneous osmotic minipumps for 4 weeks. The expression and localization of RAS components and the effect of AT 1 receptor blockade were assessed by Affymetrix microarray, qRT-PCR, Western blots, immunohistochemistry and immunofluorescence. Results-We found transcripts of most of RAS components in our microarray database, and confirmed their expression by qRT-PCR. Angiotensinogen (Aogen), angiotensin-converting enzyme (ACE) and AT 1 receptors were localized to the endothelium. There was no evidence of AT 2 receptor localization in the microvascular endothelium. In SHR, (pro)renin receptor mRNA and AT 1 receptor mRNA and protein expression were higher, whereas Aogen, ACE mRNA and AT 2 receptor mRNA and protein expression were lower than in WKY rats. Candesartan treatment increased Aogen, ACE and AT 2 receptor in SHR, and increased ACE and decreased Aogen in WKY rats, without affecting the (pro)renin and AT 1 receptors. Conclusions-Increased (pro)renin and AT 1 receptor expression in SHR substantiates the importance of the local RAS overdrive in the cerebrovascular pathophysiology in hypertension. AT 1 receptor blockade and increased AT 2 receptor stimulation after administration of candesartan may contribute to the protection against brain ischemia and inflammation.