title: Refinement of the ipsilateral retinocollicular projection is disrupted in double endothelial and neuronal nitric oxide synthase gene knockout mice.
abstract: Development of retinal connections to the superior colliculus (SC) requires an activity dependent refinement process in which axons gradually become restricted to appropriate retinotopic locations. Nitric oxide has been implicated in this process. We tested this possibility by studying the refinement of the ipsilateral retinocollicular projections (IRP) in normal C57-BL/6 mice and in double knockout mice in which the genes for the edothelial and neuronal isoforms of nitric oxide synthase (e, nNOS) were disrupted. Mice aged between P19 and adulthood were perfused 44-48 h after anterograde injections of WGA-HRP into one eye in order to measure the distribution of the labeled IRP. In normal mice, segregation of the IRP was complete at P21, with the ipsilateral projection restricted to the rostro-medial SC. By contrast, the ipsilateral projection was spread over much more of the SC in double e, nNOS knockouts at P21 with patches of label distributed across the entire medio-lateral axis of the rostral 700 microm. Although the distribution of the ipsilateral projection became more restricted in knockout animals at later ages, it was still more extensive than that of normal mice of the same age at P28 and P42. In the adult, the distribution of axons was similar in both normal and double knockout animals. These results show that refinement of the IRP is delayed when expression of eNOS and nNOS is disrupted, presumably to axons with uncorrelated activity because nitric oxide serves as a repellant molecule during normal development.
authors.affiliation: Department of Cell Biology and Anatomy and The Neuroscience Center, Louisiana State University Health Sciences Center, 1901 Perdido Street, New Orleans, LA, USA.
authors.forename: H H
authors.initials: HH
authors.lastname: Wu
authors.forename: R J
authors.initials: RJ
authors.lastname: Cork
authors.forename: P L
authors.initials: PL
authors.lastname: Huang
authors.forename: D L
authors.initials: DL
authors.lastname: Shuman
authors.forename: R R
authors.initials: RR
authors.lastname: Mize
mesh_terms: D000818:Animals; D004727:Endothelium / Q000201:enzymology; D018507:Gene Expression Regulation, Developmental; D015971:Gene Expression Regulation, Enzymologic; D051379:Mice; D008810:Mice, Inbred C57BL; D018345:Mice, Knockout; D009419:Nerve Tissue Proteins / Q000235:genetics; D009474:Neurons / Q000201:enzymology; D009569:Nitric Oxide / Q000378:metabolism; D019001:Nitric Oxide Synthase / Q000235:genetics*; D052248:Nitric Oxide Synthase Type I; D052247:Nitric Oxide Synthase Type II; D052250:Nitric Oxide Synthase Type III; D012160:Retina / Q000166:cytology* / Q000196:embryology / Q000201:enzymology; D013477:Superior Colliculi / Q000166:cytology* / Q000196:embryology / Q000201:enzymology; D013997:Time Factors; D014795:Visual Pathways / Q000166:cytology / Q000196:embryology / Q000201:enzymology; D018998:Wheat Germ Agglutinin-Horseradish Peroxidase Conjugate
chemical_list: D009419:Nerve Tissue Proteins; D018998:Wheat Germ Agglutinin-Horseradish Peroxidase Conjugate; D009569:Nitric Oxide; D019001:Nitric Oxide Synthase; D052248:Nitric Oxide Synthase Type I; D052247:Nitric Oxide Synthase Type II; D052250:Nitric Oxide Synthase Type III; C496321:Nos1 protein, mouse; C496315:Nos3 protein, mouse