Neuro-Immune Modulation of Cholinergic Signaling in an Addiction Vulnerability Trait

Sign-tracking (ST) describes the propensity to approach and contact a Pavlovian reward cue. By contrast, goal -trackers (GTs) respond to such a cue by retrieving the reward. These behaviors index the presence of opponent cognitive-motivational traits, with STs exhibiting attentional control deficits, behavior dominated by incentive mo-tivational processes, and vulnerability for addictive drug taking. Attentional control deficits in STs were previously attributed to attenuated cholinergic signaling, resulting from deficient translocation of intracellular choline trans-porters (CHTs) into synaptosomal plasma membrane. Here, we investigated a posttranslational modification of CHTs, poly-ubiquitination, and tested the hypothesis that elevated cytokine signaling in STs contributes to CHT modification. We demonstrated that intracellular CHTs, but not plasma membrane CHTs, are highly ubiquitinated in male and female sign-tracking rats when compared with GTs. Moreover, levels of cytokines measured in cor-tex and striatum, but not spleen, were higher in STs than in GTs. Activation of the innate immune system by sys-temic administration of the bacterial endotoxin lipopolysaccharide (LPS) elevated ubiquitinated CHT levels in cortex and striatum of GTs only, suggesting ceiling effects in STs. In spleen, LPS increased levels of most cyto-kines in both phenotypes. In cortex, LPS particularly robustly increased levels of the chemokines CCL2 and CXCL10. Phenotype-specific increases were restricted to GTs, again suggesting ceiling effects in STs. These re-sults indicate that interactions between elevated brain immune modulator signaling and CHT regulation are es-sential components of the neuronal underpinnings of the addiction vulnerability trait indexed by sign-tracking.

Automated summary

Sign-tracking rats have higher levels of cytokines and poly-ubiquitinated CHTs in the brain compared to goal-trackers. Activation of the immune system increases cytokines and ubiquitinated CHTs only in goal-trackers, indicating a connection between immune modulator signaling and addiction vulnerability.