Editing of serotonin 2C receptor mRNA in the prefrontal cortex characterizes high-novelty locomotor response behavioral trait

Serotonin 2C receptor (5-HT_2CR) exerts a major inhibitory influence on dopamine (DA) neurotransmission within the mesocorticolimbic DA pathway that is implicated in drug reward and goal-directed behaviors. 5-HT _2CR pre-mRNA undergoes adenosine-to-inosine editing, generating numerous receptor isoforms in brain. As editing influences 5-HT_2CR activity, individual differences in editing might influence dopaminergic function and, thereby, contribute to interindividual vulnerability to drug addiction. Liability to drug-related behaviors in rats can be predicted by their level of motor activity in response to a novel environment. Rats with a high locomotor response (high responders; HRs) exhibit enhanced acquisition and maintenance of drug self-administration compared to rats with a low response (low responders; LRs). We here examined 5-HT_2CR mRNA editing and expression in HR and LR phenotypes to investigate the relationship between 5-HT_2CR function and behavioral traits relevant to drug addiction vulnerability. Three regions of the mesocorticolimbic circuitry (ventral tegmental area (VTA), nucleus accumbens (NuAc) shell, and medial prefrontal cortex (PFC)) were examined. 5-HT_2CR mRNA expression and editing were significantly higher in the NuAc shell compared with both the PFC and VTA, implying significant differences in function (including constitutive activity) among 5-HT_2CR neuronal populations within the circuitry. The regional differences in editing could, at least in part, arise from the variations in expression levels of the editing enzyme, ADAR2, and/or from the variations in the ADAR2/ADAR1 ratio observed in the study. No differences in the 5-HT _2CR expression were detected between the behavioral phenotypes. However, editing was higher in the PFC of HRs vs LRs, implicating this region in the pathophysiology of drug abuse liability.