title: Gi-DREADD Expression in Peripheral Nerves Produces Ligand-Dependent Analgesia, as well as Ligand-Independent Functional Changes in Sensory Neurons.
abstract: Designer receptors exclusively activated by designer drugs (DREADDs) are an advanced experimental tool that could potentially provide a novel approach to pain management. In particular, expression of an inhibitory (Gi-coupled) DREADD in nociceptors might enable ligand-dependent analgesia. To test this possibility, TRPV1-cre mice were used to restrict expression of Gi-DREADDs to predominantly C-fibers. Whereas baseline heat thresholds in both male and female mice expressing Gi-DREADD were normal, 1 mg/kg clozapine-N-oxide (CNO) produced a significant 3 h increase in heat threshold that returned to baseline by 5 h after injection. Consistent with these behavioral results, CNO decreased action potential firing in isolated sensory neurons from Gi-DREADD mice. Unexpectedly, however, the expression of Gi-DREADD in sensory neurons caused significant changes in voltage-gated Ca2+and Na+currents in the absence of CNO, as well as an increase in Na+channel (NaV1.7) expression. Furthermore, CNO-independent excitatory and inhibitory second-messenger signaling was also altered in these mice, which was associated with a decrease in the analgesic effect of endogenous inhibitory G-protein-coupled receptor activation. These results highlight the potential of this exciting technology, but also its limitations, and that it is essential to identify the underlying mechanisms for any observed behavioral phenotypes.
  
  
  
  DREADD technology is a powerful tool enabling manipulation of activity and/or transmitter release from targeted cell populations. The purpose of this study was to determine whether inhibitory DREADDs in nociceptive afferents could be used to produce analgesia, and if so, how. DREADD activation produced a ligand-dependent analgesia to heat in vivo and a decrease in neuronal firing at the single-cell level. However, we observed that expression of Gi-DREADD also causes ligand-independent changes in ion channel activity and second-messenger signaling. These findings highlight both the potential and the limitations of this exciting technology as well as the necessity to identify the mechanisms underlying any observed phenotype.
authors: Departments of Neurobiology and.
authors: Jami L
authors: 0000-0001-6093-6511
authors: JL
authors: Saloman
authors: Anesthesiology, University of Pittsburgh, School of Medicine, Pittsburgh, Pennsylvania 15261.
authors: Nicole N
authors: NN
authors: Scheff
authors: Departments of Neurobiology and.
authors: Lindsey M
authors: LM
authors: Snyder
authors: Departments of Neurobiology and.|Anesthesiology, University of Pittsburgh, School of Medicine, Pittsburgh, Pennsylvania 15261.
authors: Sarah E
authors: SE
authors: Ross
authors: Departments of Neurobiology and bmd1@pitt.edu.
authors: Brian M
authors: BM
authors: Davis
authors: Departments of Neurobiology and.
authors: Michael S
authors: MS
authors: Gold
mesh_terms: D000698:Analgesia; D000818:Animals; D001522:Behavior, Animal / Q000187:drug effects; D015220:Calcium Channels / Q000187:drug effects; D003024:Clozapine / Q000494:pharmacology; D015198:Designer Drugs / Q000494:pharmacology*; D005260:Female; D008297:Male; D051379:Mice; D009619:Nociceptors / Q000187:drug effects; D010147:Pain Measurement / Q000187:drug effects; D017288:Pain Threshold / Q000187:drug effects; D018408:Patch-Clamp Techniques; D010525:Peripheral Nerves / Q000378:metabolism*; D024642:Potassium Channels, Voltage-Gated / Q000187:drug effects; D043562:Receptors, G-Protein-Coupled / Q000187:drug effects; D015290:Second Messenger Systems / Q000187:drug effects; D011984:Sensory Receptor Cells / Q000187:drug effects*; D050916:TRPV Cation Channels / Q000187:drug effects
chemical_list: D015220:Calcium Channels; D015198:Designer Drugs; D024642:Potassium Channels, Voltage-Gated; D043562:Receptors, G-Protein-Coupled; D050916:TRPV Cation Channels; C493921:TRPV1 protein, mouse; D003024:Clozapine
keywords: DREADD; GPCR; analgesia; nociception; pain; second messenger