Research report Expression analysis of brain-derived neurotrophic factor (BDNF) mRNA isoforms after chronic and acute antidepressant treatment Mario Altieri a, * , Francesca Marini b , Roberto Arban a , Giovanni Vitulli a , Birger O. Jansson a,1 a Centre of Excellence for Drug Discovery, Psychiatry, GlaxoSmithKline Research Centre, via Fleming 4, I-37135 Verona, Italy b Department of Medicine and Public Health, Section of Pharmacology, School of Medicine, University of Verona, Policlinico Borgo Roma, I-37134 Verona, Italy Accepted 18 December 2003 Abstract The neurotrophin brain-derived neurotrophic factor (BDNF) is considered to be a key factor for neuronal survival, differentiation and plasticity. According to a proposed hypothetical model BDNF expression might play a central role in the pathogenesis of depression. The BDNF gene is rather complex in its structure and it can express four different mRNA isoforms by alternative splicing, each producing the same protein. This might reflect fine tuning of gene regulation by different signalling networks. Since the BDNF gene has been reported to be upregulated by antidepressants, the expression of the four BDNF mRNA isoforms was measured by real-time quantitative RT-PCR in rat hippocampi after chronic and acute treatment with the antidepressant drug fluoxetine and GR205171, a selective NK-1 receptor antagonist with anxiolytic-like properties. The aim of this study was to test the hypothesis of differential regulation of the mRNA isoforms by those compounds. Our results indicate that the expression of BDNF mRNA isoforms is not affected by chronic or acute treatment with fluoxetine or GR205171. D 2004 Elsevier B.V. All rights reserved. Theme: Development and regeneration Topic: Neurotrophic factors: expression and regulation Keywords: Gene expression; Alternative splicing; Hippocampus; Depression; Fluoxetine; Rat 1. Introduction Brain-derived neurotrophic factor (BDNF) belongs to the family of neurotrophins [2], secreted polypeptides which regulate neuronal survival [8] differentiation and plasticity [22]. The regulation of BDNF has been proposed to be involved in the pathogenesis of depression. According to this model [6], chronic stress leads to a long-term decreased expression of BDNF, which makes hippocampal neurons (CA3 pyramidal cells, CA1 pyramidal cells and dentate gyrus granule cells) more vulnerable to several types of neuronal insult with consequent atrophy or damage of these cellular types. In the long term this pathological mechanism, in combination with other genetic and environmental factors could result in the development of depressive disorders [6]. Chronic (but not acute) treatment with major classes of antidepressants has been reported to increase the expression of the rat BDNF gene in CA3 and dentate gyrus, [14,15] and to change the BDNF immunoreactivity in rat hippocampus in a dose dependent manner [24], thus directly linking BDNF to the mechanism of antidepressant action. An increased expression of BDNF could reverse the proposed pathological mechanism by improving the survival of hip- pocampal neurons [6] and restoring hippocampal neuro- genesis [11]. The rat BDNF gene comprises five exons: I, II, III, IV and V (Fig. 1). Exons I, II, III and IV are non-coding (exon I contains an extra in-frame initiation codon) and the whole protein open reading frame (ORF) is encoded within exon V. Four different mRNA isoforms can be expressed by splicing each of the non-coding exons to exon V [23]. 0006-8993/$ - see front matter D 2004 Elsevier B.V. All rights reserved. doi:10.1016/j.brainres.2003.12.028 * Corresponding author. Tel.: +39-45-921-8548; fax: +39-45-921- 8047. E-mail address: mario.2.altieri@gsk.com (M. Altieri). 1 Present address: Affibody AB, Box 20137, SE-161 02 Bromma, Sweden. www.elsevier.com/locate/brainres Brain Research 1000 (2004) 148 – 155