title: Muscarinic excitation of parvalbumin-positive interneurons contributes to the severity of pilocarpine-induced seizures.
abstract: OBJECTIVE
  A common rodent model in epilepsy research employs the muscarinic acetylcholine receptor (mAChR) agonist pilocarpine, yet the mechanisms underlying the induction of pilocarpine-induced seizures (PISs) remain unclear. Global M1 mAChR (M1 R) knockout mice are resistant to PISs, implying that M1 R activation disrupts excitation/inhibition balance. Parvalbumin-positive (PV) inhibitory neurons express M1 Rs, participate in cholinergically induced oscillations, and can enter a state of depolarization block (DB) during epileptiform activity. Here, we test the hypothesis that pilocarpine activation of M1 Rs expressed on PV cells contributes to PISs.
  
  
  METHODS
  CA1 PV cells in PV-CRE mice were visualized with a floxed YFP or hM3Dq-mCherry adeno-associated virus, or by crossing PV-CRE mice with the RosaYFP reporter line. To eliminate M1 Rs from PV cells, we generated PV-M1 knockout (KO) mice by crossing PV-CRE and floxed M1 mice. Action potential (AP) frequency was monitored during application of pilocarpine (200 μm). In behavioral experiments, locomotion and seizure symptoms were recorded in wild-type (WT) or PV-M1 KO mice during PISs.
  
  
  RESULTS
  Pilocarpine significantly increased AP frequency in CA1 PV cells into the gamma range. In the continued presence of pilocarpine, a subset (5/7) of PV cells progressed to DB, which was mimicked by hM3Dq activation of Gq-receptor signaling. Pilocarpine-induced depolarization, AP firing at gamma frequency, and progression to DB were prevented in CA1 PV cells of PV-M1 KO mice. Finally, compared to WT mice, PV-M1 KO mice were associated with reduced severity of PISs.
  
  
  CONCLUSIONS
  Pilocarpine can directly depolarize PV+ cells via M1 R activation, but a subset of these cells progress to DB. Our electrophysiologic and behavioral results suggest that this mechanism is active during PISs, contributing to a collapse of PV-mediated γ-aminobutyric acid (GABA)ergic inhibition, dysregulation of excitation/inhibition balance, and increased susceptibility to PISs.
authors.affiliation: COBRE Center for Structural and Functional Neuroscience, The University of Montana, Missoula, Montana, U.S.A; Department of Biomedical and Pharmaceutical Sciences, The University of Montana, Missoula, Montana, U.S.A.
authors.forename: Feng
authors.initials: F
authors.lastname: Yi
authors.forename: Evan
authors.initials: E
authors.lastname: DeCan
authors.forename: Kurt
authors.initials: K
authors.lastname: Stoll
authors.forename: Eric
authors.initials: E
authors.lastname: Marceau
authors.forename: Karl
authors.initials: K
authors.lastname: Deisseroth
authors.forename: J Josh
authors.initials: JJ
authors.lastname: Lawrence
mesh_terms: D000200:Action Potentials / Q000187:drug effects* / Q000502:physiology; D000818:Animals; D004195:Disease Models, Animal; D006624:Hippocampus / Q000187:drug effects; D007395:Interneurons / Q000187:drug effects; D051379:Mice; D018345:Mice, Knockout; D010320:Parvalbumins / Q000378:metabolism*; D010862:Pilocarpine / Q000633:toxicity; D011976:Receptors, Muscarinic / Q000187:drug effects*; D012640:Seizures / Q000139:chemically induced / Q000188:drug therapy*
chemical_list: D010320:Parvalbumins; D011976:Receptors, Muscarinic; D010862:Pilocarpine
keywords: Acetylcholine; Hippocampus; Muscarinic; Pilocarpine; Seizures