Chronic systemic injection of DREADD agonists Clozapine-N-oxide and Compound 21 does not change behavior relevant to locomotion, exploration, anxiety, or affect in male mice

Abstract

Designer Receptors Exclusively Activated by Designer Drugs (DREADDs) are chemogenetic tools commonly-used to manipulate brain activity. The most widely-used synthetic DREADD ligand, clozapine-N-oxide (CNO), is back-metabolized to clozapine which can itself activate endogenous receptors. Studies in non-DREADD-expressing rodents suggest CNO or a DREADD agonist that lacks active metabolites, such as Compound 21 (C21), change rodent behavior (e.g. decrease locomotion), but chronic injection of CNO does not change locomotion. However, it is unknown if chronic CNO changes behaviors relevant to locomotion, exploration, anxiety, and depression, or if chronic C21 changes any aspect of mouse behavior. Here non-DREADD-expressing mice received i.p. Vehicle (Veh), CNO, or C21 (1mg/kg) 5 days/week for 16 weeks and behaviors were assessed over time. Veh, CNO, and C21 mice had similar weight gain over the 16-week-experiment. During the 3rd injection week, CNO and C21 mice explored more than Veh mice in a novel context and had more open field center entries; however, groups were similar in other measures of locomotion and anxiety. During the 14th-16th injection weeks, Veh, CNO, and C21 mice had similar locomotion and anxiety-like behaviors. We interpret these data as showing chronic Veh, CNO, and C21 injections given to male non-DREADD-expressing mice largely lack behavioral effects. These data may be helpful for behavioral neuroscientists when study design requires repeated injection of these DREADD agonists. HighlightsO_LIAcute injection of CNO changes behavior of non-DREADD-expressing mice C_LIO_LIIts not known if chronic CNO or alternative agonist C21 also changes mouse behavior C_LIO_LIDREADD agonists or Veh were given chronically to non-DREADD-expressing mice C_LIO_LICNO and C21 dont change locomotion and have a mixed effect on anxiety-like behavior C_LIO_LI1 mg/kg CNO and C21 can be injected repeatedly without non-specific behavior effects C_LI