The individual vulnerability to develop compulsive adjunctive behavior is associated with the recruitment of activity-regulated cytoskeleton-associated protein (Arc) within the Locus Coeruleus

Some compulsive disorders have been considered to stem from the loss of control over coping strategies, such as displacement. However, the cellular mechanisms involved in the acquisition of coping behaviors and their ensuing compulsive manifestation in vulnerable individuals have not been elucidated. Considering the role of the locus coeruleus (LC) noradrenaline dependent system in stress and related excessive behaviors, we hypothesised that neuroplastic changes in the LC may be involved in the acquisition of an adjunctive polydipsic water drinking, a prototypical displacement behavior, and the subsequent development of compulsion in vulnerable individuals. Thus, male Sprague Dawley rats were characterised for their tendency, or not, to develop compulsive polydipsic drinking in a schedule-induced polydipsia (SIP) procedure before their fresh brains were harvested. A new quantification tool for RNAscope assays revealed that the development of compulsive adjunctive behavior was associated with a low mRNA copy number of the plasticity marker Arc in the LC which appeared to be driven by specific adaptations in an ensemble of tyrosine hydroxylase (TH)+, zif268-neurons. This ensemble was specifically engaged by the expression of compulsive adjunctive behavior, not by stress, because its functional recruitment was not observed in individuals that no longer had access to the water bottle before sacrifice while it consistently correlated with the levels of polydipsic water drinking only when it had become compulsive. Together these findings suggest that downregulation of Arc mRNA levels in a population of a TH+zif268-LC neurons represents a signature of the tendency to develop compulsive coping behaviors.