title: Synaptic localization of nitric oxide synthase and soluble guanylyl cyclase in the hippocampus.
abstract: Functional evidence suggests that nitric oxide released from CA1 pyramidal cells can act as a retrograde messenger to mediate hippocampal long-term potentiation, but the failure to find neuronal nitric oxide synthase (NOS-I) in the dendritic spines of these cells has cast doubt on this suggestion. We hypothesized that NOS-I may be in spines but in a form inaccessible to antibody when using standard histological fixation procedures. Supporting this hypothesis, we found that after a weak fixation protocol shown previously to enhance staining of synaptic proteins, CA1 pyramidal cells exhibit clear immunoreactivity for NOS-I. Confocal microscopy revealed that numerous dendritic spines in the stratum radiatum contained the NR2 subunit of the NMDA receptor and the adaptor protein postsynaptic density-95, and a subset of these spines also contained NOS-I. Quantitative studies showed that only approximately 8% of synaptic puncta (identified by synaptophysin staining) were associated with NOS-I, and approximately 9% contained the beta subunit of soluble guanylyl cyclase (sGC), a major target of NO. However, the majority of NOS-I-positive synaptic puncta was associated with sGC and vice versa. Postembedding immunogold electron microscopy showed that NOS-I concentrates just inside the postsynaptic plasma membrane of asymmetric axospinous synapses in the stratum radiatum of CA1, whereas sGCbeta concentrates just inside the presynaptic membrane. Together, these findings support the possibility that NO may act as a retrograde messenger to help mediate homosynaptic plasticity in a subpopulation of synapses in the stratum radiatum of CA1.
authors.affiliation: Department of Cell and Developmental Biology, University of North Carolina, Chapel Hill, North Carolina 27599, USA. alain_burette@med.unc.edu
authors.forename: Alain
authors.initials: A
authors.lastname: Burette
authors.forename: Ulrike
authors.initials: U
authors.lastname: Zabel
authors.forename: Richard J
authors.initials: RJ
authors.lastname: Weinberg
authors.forename: Harald H H W
authors.initials: HH
authors.lastname: Schmidt
authors.forename: Juli G
authors.initials: JG
authors.lastname: Valtschanoff
mesh_terms: D000818:Animals; D000918:Antibody Specificity; D002452:Cell Count; D003712:Dendrites / Q000378:metabolism / Q000648:ultrastructure; D006162:Guanylate Cyclase; D006624:Hippocampus / Q000166:cytology / Q000378:metabolism*; D007150:Immunohistochemistry; D007527:Isoenzymes / Q000096:biosynthesis; D017774:Long-Term Potentiation / Q000502:physiology; D008297:Male; D051379:Mice; D018345:Mice, Knockout; D009419:Nerve Tissue Proteins / Q000378:metabolism; D019001:Nitric Oxide Synthase / Q000096:biosynthesis*; D052248:Nitric Oxide Synthase Type I; D020033:Protein Isoforms / Q000096:biosynthesis; D017966:Pyramidal Cells / Q000166:cytology / Q000378:metabolism; D051381:Rats; D017207:Rats, Sprague-Dawley; D018160:Receptors, Cytoplasmic and Nuclear / Q000096:biosynthesis*; D016194:Receptors, N-Methyl-D-Aspartate / Q000096:biosynthesis; D000071756:Soluble Guanylyl Cyclase; D013569:Synapses / Q000378:metabolism* / Q000648:ultrastructure; D016707:Tissue Fixation / Q000379:methods
chemical_list: D007527:Isoenzymes; C120997:NR2A NMDA receptor; D009419:Nerve Tissue Proteins; D020033:Protein Isoforms; D018160:Receptors, Cytoplasmic and Nuclear; D016194:Receptors, N-Methyl-D-Aspartate; C033652:postsynaptic density proteins; D019001:Nitric Oxide Synthase; D052248:Nitric Oxide Synthase Type I; C496321:Nos1 protein, mouse; C496322:Nos1 protein, rat; D006162:Guanylate Cyclase; D000071756:Soluble Guanylyl Cyclase