Abstract
Designer Receptors Exclusively Activated by Designer Drugs (DREADDs) are an important tool for modulating and understanding neural circuits. Depending on the DREADD system used, DREADD-targeted neurons can be activated or repressed in vivo following a dose of the DREADD agonist clozapine-N-oxide (CNO). Because DREADD experiments often involve behavioral assays, the method of CNO delivery is important. Currently, the most common delivery method is intraperitoneal (IP) injection. IP injection is both a fast and reliable technique, but it is painful and stressful particularly when many injections are required. We sought an alternative CNO delivery paradigm, which would retain the speed and reliability of IP injections without being as invasive. Here, we show that CNO can be effectively delivered topically via eye-drops. Eye-drops robustly activated DREADD-expressing neurons in the brain and peripheral tissues and does so at the same dosages as IP injection. Eye-drops provide an easier, less invasive and less stressful method for activating DREADDs in vivo.
Highlights
Scientists have developed a variety of methods to modulate targeted neuronal subpopulation in vivo to understand the neuronal circuits underlying behavior
A class named Designer Receptors Exclusively Activated by Designer Drugs (DREADDs) have emerged as the primary chemogenetic tool for modulation of specific cell types (Armbruster et al, 2007)
We quantified the percentage of DREADDmCherry+ cells clearly expressing c-Fos following saline and each dose of CNO [Saline: 8 of 272 cells (2.9%); 0.001 mg/kg CNO: 12 of 241 (4.98%); 0.01 mg/kg: 4 of 213 (1.88%); 0.1 mg/kg: 99 of 381 (25.99%); 1.0 mg/kg: 256 of 263 (97.34%)] (Figure 1C). 1.0 mg/kg CNO appears to be an effective dose for robust activation of DREADD-expressing neurons in the brain
Summary
Scientists have developed a variety of methods to modulate targeted neuronal subpopulation in vivo to understand the neuronal circuits underlying behavior Two such methods have become commonplace in modern neuroscience: chemogenetics and optogenetics. DREADDs can be introduced virally or using an expanding collection of transgenic mice (Alexander et al, 2009; Guettier et al, 2009; Ray et al, 2011; Zhu et al, 2014, 2016) Both engineered receptors are activated following introduction of the chemical clozapine-N-oxide (CNO), and are being used to robustly modulate a variety of neuronal populations in vivo (Alexander et al, 2009; Atasoy et al, 2012; Garner et al, 2012; Keenan et al, 2016; Milosavljevic et al, 2016a). Additional CNO-responsive receptors have been engineered to activate Gs signaling (Guettier et al, 2009), arrestin signaling (Nakajima and Wess, 2012), and axon specific Gi signaling (Stachniak et al, 2014)
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