Validation of a simple, ethologically relevant paradigm for assessing anxiety in mice

Background Several studies assessing volumetric measurements of regional brain structure in bipolar disorder have been published in recent years, but their results have been inconsistent. Our aim was to complete a meta-analysis of regional morphometry in bipolar disorder as assessed using magnetic resonance imaging (MRI). Methods We conducted a systematic literature search of MRI studies of bipolar disorder and identified studies which reported volume measurements in a selected number of regions. Twenty-six studies comprising volumetric measurements on up to 404 independent patients with bipolar disorder were included. A meta-analysis was carried out comparing the volumes of regions in bipolar disorder to comparison subjects using a random effects model. Results Patients with bipolar disorder had enlargement of the right lateral ventricle, but no other regional volumetric deviations which reached significance. Strong heterogeneity existed for several regions, including the third ventricle, left subgenual prefrontal cortex, bilateral amygdala and thalamus. Conclusions Regional volume of most structures we studied is preserved in bipolar disorder as a whole, which was significantly associated only with right-sided ventricular enlargement. However the extensive heterogeneity detected indicates the need for further studies to establish if consistent regional brain volume deviation exists in bipolar disorder or in specific clinical subsets of the illness.