Dissociation of Molecular and Behavioral Neuroadaptations Following Acute GRK2/3 Inhibition in Amphetamine-Treated Rats

BackgroundIndividual vulnerability to addiction is driven by neuroadaptations within dopaminergic circuits. G protein-coupled receptor kinases (GRKs), specifically GRK2 and GRK3 regulate D2 receptor (D2R) signaling and trafficking, but their role in amphetamine (AMPH)-induced locomotor sensitization remains unclear. This study aimed to determine whether GRK2/3 inhibition alters locomotor sensitization and its associated molecular correlates across striatal regions. MethodsAdult rats (n = 39) were assigned to saline, acute AMPH, or repeated AMPH groups and received intraperitoneal administration of vehicle or the GRK2/3 inhibitor Cmpd101 (1.0 mg/kg intraperitoneally, i.p.). Locomotor activity was assessed under basal and injection conditions to evaluate sensitization. Protein levels of D2R, GRK2, and GRK5 were quantified across striatal regions using Western blot and analyzed with linear mixed models. ResultsRepeated AMPH exposure induced locomotor sensitization in a subset of animals, but Cmpd101 did not significantly modify locomotor activity or sensitization expression. At the molecular level, Cmpd101 had no effect on D2R levels and produced selective, region-dependent changes in GRK2 and GRK5. Notably, GRK2/3 inhibition altered the relationship between protein expression and locomotor sensitization in a region-specific manner, rather than inducing consistent changes in absolute protein levels. ConclusionsGRK2/3 inhibition by Cmpd101 produces region-specific molecular effects and reshapes protein-behavior relationships without significantly altering locomotor sensitization. These findings support a model in which GRKs act as context-dependent modulators of dopaminergic signaling rather than direct drivers of behavioral output.