title: Comparison of gene expression profiles in the blood, hippocampus and prefrontal cortex of rats.
abstract: BACKGROUND
  The comparability of gene expression between blood and brain tissues is a central issue in neuropsychiatric research where the analysis of molecular mechanisms in the brain is of high importance for the understanding of the diseases and the discovery of biomarkers. However, the accessibility of brain tissue is limited. Therefore, knowledge about how easily accessible peripheral tissue, e. g. blood, is comparable to and reflects gene expression of brain regions will help to advance neuropsychiatric research.
  
  
  METHODS
  Gene expression in the blood, hippocampus (HC) and prefrontal cortex (PFC) of genetically identical rats was compared using a genome-wide Affymetrix gene expression microarray covering 29,215 expressed genes. A total of 56.8% of 15,717 expressed genes were co-expressed in blood and at least one brain tissue, while 55.3% of all genes were co-expressed in all three tissues simultaneously. The overlapping genes included a set of genes of relevance to neuropsychiatric diseases, in particular bipolar disorder, schizophrenia and alcohol addiction. These genes included CLOCK, COMT, FAAH, NPY, NR3C1, NRGN, PBRM1, TCF4, and SYNE.
  
  
  CONCLUSIONS
  This study provides baseline data on absolute gene expression and differences between gene expression in the blood, HC and PFC brain tissue of genetically identical rats. The present data represents a valuable resource for future studies as it might be used for first information on gene expression levels of genes of interest in blood and brain under baseline conditions. Limitations of our study comprise possible contamination of brain tissue with blood and the non-detection of genes with very low expression levels. Genes that are more highly expressed in the brain than in the blood are of particular interest since changes in their expression, e.g. due to disease status, or treatment, are likely to be detected in an experiment. In contrast, genes with higher expression in the blood than in the brain are less informative since their higher baseline levels could superimpose variation in brain.
authors.affiliation: Department of Genetic Epidemiology in Psychiatry, Central Institute of Mental Health, Medical Faculty Mannheim/Heidelberg University, J5, 68159 Mannheim, Germany.
authors.forename: Stephanie H
authors.initials: SH
authors.lastname: Witt
authors.affiliation: Institute of Psychopharmacology, Central Institute of Mental Health, Medical Faculty Mannheim/Heidelberg University, J5, 68159 Mannheim, Germany.
authors.forename: Wolfgang H
authors.initials: WH
authors.lastname: Sommer
authors.affiliation: Institute of Psychopharmacology, Central Institute of Mental Health, Medical Faculty Mannheim/Heidelberg University, J5, 68159 Mannheim, Germany.
authors.forename: Anita C
authors.initials: AC
authors.lastname: Hansson
authors.affiliation: Medical Research Center, University Hospital Mannheim, Medical Faculty Mannheim/Heidelberg University, Theodor-Kutzer-Ufer 1-3, 68167 Mannheim, Germany.
authors.forename: Carsten
authors.initials: C
authors.lastname: Sticht
authors.affiliation: Department of Genetic Epidemiology in Psychiatry, Central Institute of Mental Health, Medical Faculty Mannheim/Heidelberg University, J5, 68159 Mannheim, Germany.
authors.forename: Marcella
authors.initials: M
authors.lastname: Rietschel
authors.affiliation: Department of Anaesthesiology and Operative Intensive Care, University Hospital Mannheim, Medical Faculty Mannheim/Heidelberg University, Theodor-Kutzer-Ufer 1-3, 68167 Mannheim, Germany.
authors.forename: Christian C
authors.initials: CC
authors.lastname: Witt
keywords: Blood; Brain; Comparison; Gene expression; Rat