The aim of this work is to determine the protein modifications contributing to epigenetic changes in the nuclei of striatal neurons in response to cocaine, and, thus, to progress in our understanding of the long-term plasticity underlying behavioral modifications. In the striatum, 95% of neurons are medium-sized spiny neurons (MSNs) subdivided mainly in two populations: the D1 dopamine receptor (D1)-expressing neurons participating in the direct pathway and the D2 dopamine receptor (D2)- expressing neurons participating in the indirect pathway. This segregation confers to dopamine the ability to exert opposite functional modulation of the two pathways. With this heterogeneous neuronal composition, analyzing lysates from pooled neuronal populations would average the responses. Taking this into consideration, we developed an assay, using flow cytometric analysis, to quantify the cocaine-induced changes in histone acetylation and methylation, and the enzyme controlling them, in the isolated D1 and D2 MSNs subpopulations. We found that D1 and D2 MSNs displayed remarkable epigenetic specificities dynamically regulated by acute and chronic cocaine. In particular, we showed that H3K14, H4K5, H4K12 acetylation and H3K9 methylation exhibit opposite regulation between the two cell types underlying the differential gene expression occurring in D1 and D2 MSNs. Finally, we showed that there is complex correlation between histone PTMs that is altered by cocaine and is cell-type dependent. We propose an original approach in neuroscience that allows to explore nuclear protein changes from virtually all neurons in basal, drug-altered or pathological conditions
