Epigenetic marks are established according to the environment and individual experiences. During brain development, they participate to the activity of neural circuits and contribute to the establishment and maintenance of several behaviours. Among them, cytosine methylation (5mC), one of the most studied modifications in the brain, is particularly sensitive to adverse environments. Recently, cytosine hydroxymethylation (5hmC), an abundant and stable mark derived from 5mC found in synaptic genes and enriched in fetal brain, has emerged as another major contributor to behavioral disturbances. These 2 important epigenetic markers constitute plausible molecular substrates in embedding the long-term effects of a maternal early experience on gene expression in brain structures linked to olfaction and odor-mediated behaviors that deserve to be studied. However, the quantification of 5hmC is still a bottleneck in our hands. This project aims to develop new tools to 1) map them by immunolabeling in olfactory tissues and 2) develop a method to quantify their variations in the olfactory bulb of offspring born a mother fed or not an obesogenic diet that display olfactory deficits (Panchenko et al., 2019). METHODS Immunohistochemistry: OB were dissected out from experimental samples, fixed 48h in PFA, cryoprotected in sucrose 30% for 48h, embedded in Tissue-Tek, then cut at 14 mm. Imunolabelling processing was adapted from Wilson et al., 2021, with few adjustments: slides were treated with glycine 0.1M for 30 min before demasking,, DNA was denaturated with 2N HCl, non specific sites were saturated with 2% BSA.