, 2007). In addition to dexamethasone treatment during pregnancy, PNS rats were show to have reduced amygdala volume and decreased numbers of both neurons and glia compared with controls (Kawamura et al., 2006). Taken together these data clearly indicate that glucocorticoid exposure during PNS may alter neuronal development, which in turn may mediate the adult PNS phenotype. The discussed mechanisms indicate that during prenatal stress signals from the dam, like heightened

glucocorticoid levels, heightened sympathetic activation, may inform the fetus about the external environmental conditions leading to alterations to neuronal development. Although the placenta may buffer some of these signals, one may argue that the buffering function of the placenta may serve to distinguish between short term and moderate environmental disturbances from Bcr-Abl inhibitor long term, more severe environmental disturbances. Again, these adaptations may be beneficial under Cell Cycle inhibitor matching prenatal and postnatal environments, however, when a mismatch occurs this may lead

to pathology. Epigenetics refers to chemical modifications to the DNA that result in alterations in gene expression without changing the DNA sequence itself. Epigenetic alterations can occur through different mechanisms such as DNA methylation, histone modification and non-coding RNAs (reviewed in (Berger et al., 2009)). Effects of exposure to early life stress (via reduced maternal licking and grooming during the neonatal period) on glucocorticoid receptor (GR, Nr3c1) DNA methylation has been reported ( Weaver et al., 2004). Casein kinase 1 Rats reared by low licking and grooming dams had a higher percentage of DNA methylation of the exon 17 of the GR promoter and had associated lower nr3c1 expression in the hippocampus ( Weaver et al., 2004). Decreased hippocampal GR may result in decreased negative feedback through GR leading to a prolonged elevation of corticosterone after stress. Mice exposed to PNS (via variable stress) during the first week of gestation were shown to have increased DNA methylation of the GR promoter

region in the hypothalamus ( Mueller and Bale, 2008). To date, similar effects on the GR DNA methylation in the offspring of dams stressed during the last week of gestation have not been reported. In the previous paragraphs we introduced FKBP5 as a potential modulator of GR signaling in the PNS model. To date no direct evidence has been presented that PNS alters DNA methylation of the FKBP5 gene. However a study in mice suggested that FKBP5 DNA methylation was decreased in mice treated with corticosterone (Lee et al., 2011). This suggests that the FKBP5 gene is susceptible to epigenetic alterations induced by glucocorticoids. Further research is needed to elucidate whether PNS exposure alters the epigenetic profile of this gene. Corticotrophin releasing hormone (CRH) is another gene that may be epigenetically altered during PNS exposure.