microRNA regulation related to the protective effects of environmental enrichment against cocaine-seeking behavior

MicroRNAs are “master regulators” of gene expression. To investigate microRNAs involved in the incentive motivation for cocaine elicited by exposure to cocaine-associated cues, we conducted NanoString nCounter analyses of microRNA expression in the nucleus accumbens shell of male rats that had been tested for cue reactivity in a previous study. These rats had been trained to self-administer cocaine while living in isolate housing, then during a subsequent 21-day forced abstinence period they either stayed under isolate housing or switched to environmental enrichment (EE), as this EE intervention is known to decrease cocaine seeking. This allowed us to create groups of “high” and “low” cocaine seekers using a median split of cocaine-seeking behavior. We conducted a differential expression analysis across these two groups that identified 33 miRNAs that were differentially altered in the nucleus accumbens shell. Predicted mRNA targets of these microRNAs are implicated in synaptic plasticity and neuronal signaling. Some of these microRNAs have previously been implicated in substance use disorders, while others are predicted to target large numbers of cocaine-related genes. Of the 33 differentially expressed microRNAs, 8 were specifically downregulated in the low-seeking group and another set of 8 had expression levels that were significantly correlated with cocaine-seeking. These findings suggest that processes involved in cocaine-seeking behavior may alter, or be altered by, multiple microRNAs. Further research examining the mechanisms involved in these microRNA changes and their effects on signaling may reveal novel therapeutic targets for attenuating drug craving. 12 samples (no replicates) of total RNA from the nucleus accumbens shell was collected from male Sprague-Dawley rats. miRNA expression analysis was performed using the Nanostring nCounter platform. Differential expression was performed using "limma" in R