title: Late-onset inner retinal dysfunction in mice lacking sigma receptor 1 (σR1).
abstract: OBJECTIVE
  Sigma receptor 1 (σR1) is expressed abundantly in the eye, and several reports suggest that this putative molecular chaperone plays a role in lens cell survival, control of intraocular pressure (IOP), and retinal neuroprotection. The present study examined the consequence of the absence of σR1 on ocular development, structure, and function.
  
  
  METHODS
  Wild-type (σR1⁺/⁺), heterozygous (σR1⁺/⁻), and homozygous (σR1⁻/⁻, knockout) mice aged 5 to 59 weeks were subjected to comprehensive electrophysiological testing and IOP measurement. The eyes were examined by light and electron microscopy and subjected to morphometric examination and detection of apoptosis.
  
  
  RESULTS
  Cornea and lens of σR1⁻/⁻ mice were similar to wild-type mice in morphologic appearance at all ages examined, and IOP was within normal limits. Comprehensive ERG and morphometric analyses initially yielded normal findings in the σR1⁻/⁻ mice compared with those in the wild-type. By 12 months, however, significantly decreased ERG b-wave amplitudes and diminished negative scotopic threshold responses, consistent with inner retinal dysfunction, were detected in σR1⁻/⁻ mice. Concomitant with these late-onset changes were increased TUNEL- and active caspase 3-positive cells in the inner retina and significant loss of cells in the ganglion cell layer, particularly in the central retina. Before these functional and structural abnormalities, there was ultrastructural evidence of axonal disruption in the optic nerve head of σR1⁻/⁻ mice as early as 6 months of age, although there were no alterations observed in retinal vascularization in σR1⁻/⁻ mice.
  
  
  CONCLUSIONS
  These data suggest that lack of σR1 leads to development of late-onset retinal dysfunction with similarities to optic neuropathy.
authors.affiliation: Department of Cellular Biology and Anatomy, Medical College of Georgia, Georgia Health Sciences University, Augusta, Gerogia, USA.
authors.forename: Yonju
authors.initials: Y
authors.lastname: Ha
authors.forename: Alan
authors.initials: A
authors.lastname: Saul
authors.forename: Amany
authors.initials: A
authors.lastname: Tawfik
authors.forename: Cory
authors.initials: C
authors.lastname: Williams
authors.forename: Kathryn
authors.initials: K
authors.lastname: Bollinger
authors.forename: Robert
authors.initials: R
authors.lastname: Smith
authors.forename: Masanori
authors.initials: M
authors.lastname: Tachikawa
authors.forename: Eric
authors.initials: E
authors.lastname: Zorrilla
authors.forename: Vadivel
authors.initials: V
authors.lastname: Ganapathy
authors.forename: Sylvia B
authors.initials: SB
authors.lastname: Smith
mesh_terms: D000818:Animals; D001369:Axons / Q000378:metabolism / Q000648:ultrastructure; D015153:Blotting, Western; D053148:Caspase 3 / Q000378:metabolism; D004195:Disease Models, Animal; D004596:Electroretinography; D019084:Fluorescent Antibody Technique, Indirect; D015870:Gene Expression; D005838:Genotype; D020287:In Situ Nick-End Labeling; D007429:Intraocular Pressure; D051379:Mice; D008810:Mice, Inbred C57BL; D018345:Mice, Knockout; D009898:Optic Disk / Q000378:metabolism / Q000648:ultrastructure; D009901:Optic Nerve Diseases / Q000378:metabolism / Q000473:pathology / Q000503:physiopathology*; D012333:RNA, Messenger / Q000378:metabolism; D017480:Receptors, sigma / Q000172:deficiency / Q000502:physiology*; D012160:Retina / Q000378:metabolism / Q000503:physiopathology*; D012164:Retinal Diseases / Q000378:metabolism / Q000473:pathology / Q000503:physiopathology*; D012165:Retinal Ganglion Cells / Q000378:metabolism / Q000648:ultrastructure; D020133:Reverse Transcriptase Polymerase Chain Reaction; D000097605:Sigma-1 Receptor
chemical_list: D053148:Caspase 3; D012333:RNA, Messenger; D017480:Receptors, sigma; D000097605:Sigma-1 Receptor; C505409:Casp3 protein, mouse