title: Axonal myelin increase in the callosal genu in depression but not schizophrenia.
abstract: BACKGROUND
  Abnormalities in the anterior inter-hemispheric connectivity have previously been implicated in major depressive disorder. Disruptions in fractional anisotropy in the callosum and fornix have been reported in schizophrenia and major depressive disorder. Oligodendrocyte density and overall size of the callosum and fornix show no alteration in either illness, suggesting that gross morphology is unchanged but more subtle organizational disruption may exist within these brain regions in mood and affective disorders.
  
  
  METHODS
  Using high-resolution oil-immersion microscopy we examined the cross-sectional area of the nerve fibre and the axonal myelin sheath, and using standard high-resolution light microscopy we measured the density of myelinated axons. These measurements were made in the genu of the corpus callosum and the medial body of the fornix at its most dorsal point. Measures were taken in the sagittal plane in the callosal genu and in the coronal plane at the most dorsal part of the fornix body.
  
  
  RESULTS
  Cases of major depressive disorder had significantly greater mean myelin cross-sectional area (p = 0.017) and myelin thickness (p = 0.004) per axon in the genu than in control or schizophrenia groups. There was no significant change in the density of myelinated axons, and no changes observed in the fornix.
  
  
  CONCLUSIONS
  The results suggest a clear increase of myelin in the axons of the callosal genu in MDD, although this type of neuropathological study is unable to clarify whether this is caused by changes during life or has a developmental origin.
authors.affiliation: King's College London, Institute of Psychiatry,De Crespigny Park,London,UK.
authors.forename: M R
authors.initials: MR
authors.lastname: Williams
authors.affiliation: Neuropathology Unit,Division of Experimental Medicine,Imperial College London,Charing Cross Campus,London,UK.
authors.forename: P
authors.initials: P
authors.lastname: Sharma
authors.affiliation: Li Ka Shing Faculty of Medicine University of Hong Kong,Hong Kong.
authors.forename: K L
authors.initials: KL
authors.lastname: Fung
authors.affiliation: Neuropathology Unit,Division of Experimental Medicine,Imperial College London,Charing Cross Campus,London,UK.
authors.forename: R K B
authors.initials: RK
authors.lastname: Pearce
authors.affiliation: Neuropathology Unit,Division of Experimental Medicine,Imperial College London,Charing Cross Campus,London,UK.
authors.forename: S R
authors.initials: SR
authors.lastname: Hirsch
authors.affiliation: Trust HQ,West London Mental Health NHS Trust,Southall,MiddlesexUK.
authors.forename: M
authors.initials: M
authors.lastname: Maier
mesh_terms: D000328:Adult; D001921:Brain / Q000473:pathology; D015331:Cohort Studies; D003337:Corpus Callosum / Q000473:pathology*; D003863:Depression; D003865:Major Depressive Disorder / Q000473:pathology*; D005260:Female; D006801:Humans; D008131:London; D008297:Male; D008859:Microscopy, Polarization; D008875:Middle Aged; D009186:Myelin Sheath / Q000473:pathology*; D009413:Nerve Fibers, Myelinated / Q000473:pathology*; D012044:Regression Analysis; D012559:Schizophrenia / Q000473:pathology*; D014015:Tissue Banks
keywords: Axons; callosum; depression; neuropathology