Long-term effects of combined neonatal and adolescent stress on brain-derived neurotrophic factor and dopamine receptor expression in the rat forebrain

Altered brain-derived neurotrophic factor (BDNF) signalling and dopaminergic neurotransmission have been shown in the forebrain in schizophrenia. The 'two hit' hypothesis proposes that two major disruptions during development are involved in the pathophysiology of this illness. We therefore used a 'two hit' rat model of combined neonatal and young-adult stress to assess effects on BDNF signalling and dopamine receptor expression. Wistar rats were exposed to neonatal maternal separation (MS) stress and/or adolescent/young-adult corticosterone (CORT) treatment. At adulthood the medial prefrontal cortex (mPFC), caudate putamen (CPu) and nucleus accumbens (NAc) were analysed by qPCR and Western blot. The 'two hit' combination of MS and CORT treatment caused significant increases in BDNF mRNA and protein levels in the mPFC of male, but not female rats. BDNF mRNA expression was unchanged in the CPu but was significantly reduced by CORT in the NAc. DR3 and DR2 mRNA were significantly up-regulated in the mPFC of two-hit rats and a positive correlation was found between BDNF and DR3 expression in male, but not female rats. DR2 and DR3 expression were significantly increased following CORT treatment in the NAc and a significant negative correlation between BDNF and DR3 and DR2 mRNA levels was found. Our data demonstrate male-specific two-hit effects of developmental stress on BDNF and DR3 expression in the mPFC. Furthermore, following chronic adolescent CORT treatment, the relationship between BDNF and dopamine receptor expression was significantly altered in the NAc. These results elucidate the long-term effects of 'two hit' developmental stress on behaviour.