Clozapine N-Oxide Administration Produces Behavioral Effects in Long-Evans Rats: Implications for Designing DREADD Experiments.
Clozapine N-oxide (CNO) is a ligand for a powerful chemogenetic system that can selectively inhibit or activate neurons; the so-called Designer Receptors Exclusively Activated by Designer Drugs (DREADD) system. This system consists of synthetic G-protein-coupled receptors, which are not believed to be activated by any endogenous ligand, but are activated by the otherwise inert CNO. However, it has previously been shown that the administration of CNO in humans and rats leads to detectable levels of the bioactive compounds clozapine andN-desmethylclozapine (N-Des). As a follow-up, experiments were conducted to investigate the effects of CNO in male Long-Evans rats. It was found that 1 mg/kg CNO reduced the acoustic startle reflex but had no effect on prepulse inhibition (PPI; a measure of sensorimotor gating). CNO (2 and 5 mg/kg) had no effect on the disruption to PPI induced by the NMDA antagonist phencyclidine or the muscarinic antagonist scopolamine. In locomotor studies, CNO alone (at 1, 2, and 5 mg/kg) had no effect on spontaneous locomotion, but 5 mg/kg CNO pretreatment significantly attenuated d-amphetamine-induced hyperlocomotion. In line with the behavioral results, fast-scan cyclic voltammetry found that 5 mg/kg CNO significantly attenuated the d-amphetamine-induced increase in evoked dopamine. However, the effects seen after CNO administration cannot be definitively ascribed to CNO because biologically relevant levels of clozapine andN-Des were found in plasma after CNO injection. Our results show that CNO has multiple dose-dependent effectsin vivoand is converted to clozapine andN-Des emphasizing the need for a CNO-only DREADD-free control group when designing DREADD-based experiments.
Department of Pharmacology and Toxicology, School of Medicine and Biomedical Sciences, University at Buffalo, SUNY , Buffalo, New York 14214.
Duncan A A
DA
MacLaren
Department of Biotechnical and Clinical Laboratory Sciences, University at Buffalo, SUNY , Buffalo, New York 14214.
Richard W
RW
Browne
Department of Neurobiology and Anatomy, Drexel University College of Medicine , Philadelphia, Pennsylvania 19129.
Jessica K
0000-0001-7828-1234
JK
Shaw
Department of Biotechnical and Clinical Laboratory Sciences, University at Buffalo, SUNY , Buffalo, New York 14214.
Sandhya
S
Krishnan Radhakrishnan
Department of Biotechnical and Clinical Laboratory Sciences, University at Buffalo, SUNY , Buffalo, New York 14214.
Prachi
P
Khare
Department of Neurobiology and Anatomy, Drexel University College of Medicine , Philadelphia, Pennsylvania 19129.
Rodrigo A
RA
España
Department of Pharmacology and Toxicology, School of Medicine and Biomedical Sciences, University at Buffalo, SUNY , Buffalo, New York 14214.
Stewart D
SD
Clark
D000661:Amphetamine / Q000494:pharmacology; D000818:Animals; D001307:Auditory Perception / Q000187:drug effects; D001522:Behavior, Animal / Q000187:drug effects*; D002491:Central Nervous System Agents / Q000097:blood / Q000494:pharmacology*; D003024:Clozapine / Q000008:administration & dosage / Q000031:analogs & derivatives* / Q000097:blood / Q000378:metabolism / Q000494:pharmacology; D015198:Designer Drugs; D004298:Dopamine / Q000378:metabolism; D004305:Dose-Response Relationship, Drug; D008297:Male; D009043:Motor Activity / Q000187:drug effects; D009714:Nucleus Accumbens / Q000187:drug effects / Q000378:metabolism; D010622:Phencyclidine / Q000494:pharmacology; D020318:Rats, Long-Evans; D011976:Receptors, Muscarinic / Q000378:metabolism; D017981:Receptors, Neurotransmitter / Q000378:metabolism; D012107:Research Design; D012601:Scopolamine / Q000494:pharmacology; D055139:Sensory Gating / Q000187:drug effects
D002491:Central Nervous System Agents; D015198:Designer Drugs; D011976:Receptors, Muscarinic; D017981:Receptors, Neurotransmitter; D000661:Amphetamine; D012601:Scopolamine; D010622:Phencyclidine; D003024:Clozapine; C079149:clozapine N-oxide; D004298:Dopamine
CNO; DREADDs; behavior; voltammetry