Inhibition of the rebound burst of neural progenitor cells reduces ethanol seeking in female dependent rats: Regulation by neuroimmune and endothelial changes

Alcohol use disorder (AUD) is highly prevalent in the United States with very few FDA approved treatments that do not completely reduce relapse to alcohol seeking. This is due to an incomplete understanding of the neurobiological substrates causing alcohol relapse. Previous studies in alcohol dependent male rats have shown cellular changes in the medial prefrontal cortex (mPFC), including increased oligodendrogenesis, heightened neuroimmune response, and decrease in blood-brain barrier (BBB) integrity associated with dependence induced drinking and relapse. Specifically during acute withdrawal, a proliferative burst of oligodendrocyte progenitor cells (OPCs) is prevalent in the mPFC which survive and mature into oligodendrocytes. Research focused on male rats have shown this dysfunctional production of OPCs is linked to a heightened neuroimmune response and endothelial disruption, but unclear if these changes are evident in females as well. Thus, it was investigated if these non-neuronal changes were also evident in dependent female rats. Like in males, quantitative immunohistochemistry depicted an increase in Ki-67 cells in the mPFC of females during acute withdrawal and concomitant increase in Olig2 cells during protracted abstinence. In addition, 3D structural analysis, Western blotting and ELISA detected a heightened neuroinflammatory response after relapse, with an increase in microglia soma area and cytokines levels including NF-kB, TNF-α, IL-13, and IL-10 in the mPFC. Furthermore, ELISA data showed an increase in VEGF levels indicating BBB dysfunction. The next question investigated was whether preventing this burst of OPCs in dependent female rats will decrease ethanol seeking behavior by regulating the neuroimmune responses and endothelial changes. To prevent the generation of Ki-67 cells, a pharmacogenetic approach was used, where transgenic GFAP-TK rats were orally fed a DNA synthesis inhibitor called Valcyte during maintenance through reinstatement. Valcyte treatment decreased ethanol seeking behavior during relapse and reinstatement, as well as enhanced latency to extinguish ethanol behaviors, showing decreased motivation to alcohol drinking. In addition, Valcyte prevented microglia activation in the mPFC and normalized levels of TNF-α, IL-4, and IL-6 in the plasma. However, Valcyte did not prevent endothelial damage in the mPFC, indicated by an increase in Ve-Cadherin and decrease in Claudin-5 expression. In conclusion, preventing the proliferative burst of Ki-67 cells in the mPFC during acute withdrawal decreased ethanol seeking behavior and prevented some aspects of the immune response seen during relapse and reinstatement of ethanol seeking behaviors