Extinction Training after Cocaine Self-Administration Influences the Epigenetic and Genetic Machinery Responsible for Glutamatergic Transporter Gene Expression in Male Rat Brain

Glutamate is a key excitatory neurotransmitter in the central nervous system. The balance of glutamatergic transporter proteins allows long-term maintenance of glutamate homeostasis in the brain, which is impaired during cocaine use disorder. The aim of this study was to investigate changes in the gene expression of SLC1A2 (encoding GLT-1), and SLC7A11 (encoding xCT), in rat brain structures after short-term (3 days) and long-term (10 days) extinction training using microarray analysis and quantitative real-time PCR. Furthermore, we analyzed the expression of genes encoding transcription factors, i.e., NFKB1 and NFKB2 (encoding NF-κB), PAX6, (encoding Pax6), and NFE2L2 (encoding Nrf2), to verify the correlation between changes in glutamatergic transporters and changes in their transcriptional factors and microRNAs (miRNAs; miR-124a, miR-543-3p and miR-342-3p) and confirm the epigenetic mechanism. We found reduced GLT-1 transcript and mRNA level in the prefrontal cortex (PFCTX) and dorsal striatum (DSTR) in rats that had previously self-administered cocaine after 3 days of extinction training, which was associated with downregulation of PAX6 (transcript and mRNA) and NFKB2 (mRNA) level in the PFCTX and with upregulation of miR-543-3p and miR-342-3p in the DSTR. The xCT mRNA level was reduced in the PFCTX and DSTR, and NFE2L2 transcript level in the PFCTX was decreased on the 3rd day of extinction training. In conclusion, 3-day drug-free period modulates GLT-1 and xCT gene expression through genetic and epigenetic mechanisms, and such changes in expression seem to be potential molecular targets for developing a treatment for cocaine-seeking behavior.