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
Designer Receptors Exclusively Activated by Designer Drugs (DREADDs) are a chemogenetic tool commonly-used to manipulate rodent brain circuit activity. The most widely-used synthetic ligand for DREADDs is Clozapine-N-oxide (CNO). However, CNO is back-metabolized to clozapine, which itself activates numerous endogenous receptors and therefore may influence rodent behavior. To eliminate potential off-target effects of CNO, a new DREADD agonist, Compound 21 (C21), has been proposed as an
... sed as an alternative as it lacks active metabolites. The literature is mixed on whether acute administration of CNO or C21 changes mouse behavior. In contrast, there is no substantial literature on whether chronic administration of CNO or C21 changes mouse behavior. Here we tested whether chronic injections of these two distinct DREADD agonists change key behaviors in non-designer receptor-expressing mice relative to Vehicle (Veh)-injected control mice. Mice (CamKIIα-icre males) were injected i.p. with Veh (0.5% dimethyl sulfoxide in 0.9% saline, 5ml/kg), CNO (0.2mg/ml, 1mg/kg), or C21 (0.2mg/ml, 1mg/kg) 5 days a week for 16 weeks. All three groups had similar weight gain over the 16 week-experiment, and showed similar measures in behaviors assessed during week 3 (beam breaks in a 30-min locomotion task, time in center of open field or open arms of elevated plus maze) and week 14-16 (ambulatory distance during 240-min activity monitoring, percent marbles buried, grooming time during the sucrose splash test). These data show chronic injections of CNO or C21 do not affect key behaviors as compared to chronic injections of Veh, and may be helpful for behavioral neuroscientists when study design requires repeated injection of these DREADD agonists.