title: Evidence for reduced dentate gyrus and fimbria volume in bipolar II disorder.
abstract: OBJECTIVE
  Dentate gyrus (DG)-dependent inhibition of the stress response might play an important role in mood disorders. During stress, hippocampal projections traversing the fimbria, a white matter bundle on the hippocampal surface, inhibit the hypothalamic-pituitary-adrenal (HPA) axis. The aim of the present study was to measure the volumes of the DG-cornu ammonis 4 (DG-CA4) and fimbria in patients with bipolar II disorder (BD-II) and healthy controls using a recently developed magnetic resonance imaging (MRI)-based technique.
  
  
  METHODS
  Thirty-seven individuals with a DSM-IV diagnosis of BD-II and 42 healthy controls underwent 3-Tesla MRI. Hippocampal subfield volumes were estimated using a novel segmentation algorithm implemented in FreeSurfer.
  
  
  RESULTS
  In patients with BD-II there was a significant reduction in the volume of the left [analysis of covariance (ANCOVA), F = 7.84, p = 0.006] and total (left + right) (F = 4.01, p = 0.047) DG-CA4 and left (F = 4.38, p = 0.040) and total (F = 4.15, p = 0.045) fimbria compared to healthy controls. Explorative analyses indicated a smaller left CA2-3 volume in subjects with BD-II compared to healthy controls, and a reduced left fimbria volume in unmedicated patients compared to medicated patients and controls.
  
  
  CONCLUSIONS
  Our results provide evidence for the involvement of the DG and fimbria in BD-II. Longitudinal studies of the DG and fimbria with assessments of the HPA axis in BD-II are warranted.
authors: Department of Neuropsychiatry and Psychosomatic Medicine, Oslo University Hospital, Oslo, Norway. telvsaha@ous-hf.no
authors: Torbjørn
authors: T
authors: Elvsåshagen
authors: Lars T
authors: LT
authors: Westlye
authors: Erlend
authors: E
authors: Bøen
authors: Per K
authors: PK
authors: Hol
authors: Stein
authors: S
authors: Andersson
authors: Ole A
authors: OA
authors: Andreassen
authors: Birgitte
authors: B
authors: Boye
authors: Ulrik F
authors: UF
authors: Malt
mesh_terms: D000328:Adult; D000704:Analysis of Variance; D001714:Bipolar Disorder / Q000473:pathology*; D016022:Case-Control Studies; D018891:Dentate Gyrus / Q000473:pathology*; D005260:Female; D020712:Fornix, Brain / Q000473:pathology*; D006801:Humans; D007091:Image Processing, Computer-Assisted; D008279:Magnetic Resonance Imaging; D008297:Male; D055815:Young Adult