Does chronic systemic injection of the DREADD agonists clozapine-N-oxide or Compound 21 change behavior relevant to locomotion, exploration, anxiety, and depression in male non-DREADD-expressing mice?

• Published in: Neuroscience letters Vol. 739; p. 135432
• Main Authors: Tran, Fionya H., Spears, Stella L., Ahn, Kyung J., Eisch, Amelia J., Yun, Sanghee
• Format: Journal Article
• Language: English
• Published: Ireland Elsevier B.V 20.11.2020
• Subjects: Animals; Anxiety - chemically induced; Behavior, Animal - drug effects; Chemogenetics; Clozapine - administration & dosage; Clozapine - analogs & derivatives; Clozapine back-metabolism; Depression - chemically induced; Designer Drugs - administration & dosage; Elevated plus maze; Exploratory Behavior - drug effects; Imidazoles - administration & dosage; Locomotion - drug effects; Male; Marble burying; Mice, Inbred C57BL; Mice, Transgenic; Open field; Sucrose splash test; Sulfonamides - administration & dosage; Thiophenes - administration & dosage; C21; CNO; Elevated plus maze; DREADD; h; Marble burying; i.p; Open field; min; Chemogenetics; Veh; Clozapine back-metabolism; Sucrose splash test
• ISSN: 0304-3940; 1872-7972
• DOI: 10.1016/j.neulet.2020.135432

•Acute injection of CNO changes behavior of non-DREADD-expressing mice.•It’s not known if chronic CNO or alternative agonist C21 also changes mouse behavior.•DREADD agonists or Veh were given chronically to non-DREADD-expressing mice.•CNO and C21 don’t change locomotion and have a mixed effect on anxiety-like behavior.•1 mg/kg CNO and C21 can be injected repeatedly without non-specific behavior effects. 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 (1 mg/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.