title: Clozapine and the mitogen-activated protein kinase signal transduction pathway: implications for antipsychotic actions.
abstract: BACKGROUND
  Mitogen-activated protein kinase (MAPK) signaling pathways respond to dopaminergic and serotonergic agents and mediate short- and long-term effects of intracellular signaling in neurons. Here we show that the antipsychotic agent, clozapine, selectively activates the MEK/ERK MAPK pathway, and inhibition of this pathway reverses clozapine's actions in the conditioned avoidance response (CAR) paradigm, a rodent behavioral assay of antipsychotic activity.
  
  
  METHODS
  Phosphorylation patterns of MAPK pathway enzymes were determined by quantitative immunoblot analysis and immunohistochemistry of rat prefrontal cortex. Kinase inhibitors were used to assess the role of MAPK signaling pathways in mediating clozapine-induced suppression of CAR.
  
  
  RESULTS
  Clozapine administration selectively increased phosphorylation of MEK1/2 but had no effect on p38 or JNK phosphorylation. Pretreatment with the 5-HT2A agonist (+/-)-2,5-dimethoxy-4-iodoamphetamine hydrochloride blocked the clozapine-induced increase in MEK1/2 phosphorylation. Immunohistochemistry revealed that clozapine treatment elevated the number of cells in the prefrontal cortex positive for phosphoERK, the downstream substrate of MEK1/2. Prior administration of MEK1/2 inhibitors U0126 or Sl327, or ERK inhibitor 5-iodotubercidin, reversed suppression of CAR induced by clozapine, whereas administration of vehicle, JNK or p38 inhibitors (L-JNK-1 and SB203580, respectively) had no effect. Inhibition of kinases upstream to MEK1/2 (PI-3K, PKC, and CaMKII) by administration of LY294002, bisindolylmaleimide, or KN-62, respectively, also reversed clozapine-induced suppression of CAR.
  
  
  CONCLUSIONS
  These data support the hypothesis that the MEK/ERK signal transduction cascade participates in clozapine's antipsychotic actions.
authors.affiliation: Department of Psychiatry, Scott & White Memorial Hospital, Central Texas Veterans Health Care System, and Texas A & M University System Health Science Center College of Medicine, Temple, Texas, USA. jbrowning@swmail.sw.org
authors.forename: Jeff L
authors.initials: JL
authors.lastname: Browning
authors.forename: Tushar
authors.initials: T
authors.lastname: Patel
authors.forename: Paul C
authors.initials: PC
authors.lastname: Brandt
authors.forename: Keith A
authors.initials: KA
authors.lastname: Young
authors.forename: Leigh A
authors.initials: LA
authors.lastname: Holcomb
authors.forename: Paul B
authors.initials: PB
authors.lastname: Hicks
mesh_terms: D000662:Amphetamines / Q000494:pharmacology; D000818:Animals; D014150:Antipsychotic Agents / Q000494:pharmacology*; D001362:Avoidance Learning / Q000187:drug effects*; D001522:Behavior, Animal / Q000187:drug effects; D015153:Blotting, Western / Q000379:methods; D003024:Clozapine / Q000494:pharmacology*; D003213:Conditioning, Psychological / Q000187:drug effects*; D004305:Dose-Response Relationship, Drug; D004347:Drug Interactions; D048049:Extracellular Signal-Regulated MAP Kinases / Q000378:metabolism*; D007150:Immunohistochemistry / Q000379:methods; D048728:MAP Kinase Kinase Kinase 1 / Q000378:metabolism; D048730:MAP Kinase Kinase Kinase 2 / Q000378:metabolism; D008297:Male; D010766:Phosphorylation / Q000187:drug effects; D017397:Prefrontal Cortex / Q000187:drug effects / Q000201:enzymology; D051381:Rats; D017207:Rats, Sprague-Dawley; D017366:Serotonin Receptor Agonists / Q000494:pharmacology; D015398:Signal Transduction / Q000187:drug effects*; D013722:Teprotide / Q000494:pharmacology
chemical_list: D000662:Amphetamines; D014150:Antipsychotic Agents; D017366:Serotonin Receptor Agonists; D013722:Teprotide; D048049:Extracellular Signal-Regulated MAP Kinases; D048728:MAP Kinase Kinase Kinase 1; D048730:MAP Kinase Kinase Kinase 2; D003024:Clozapine; C015952:4-iodo-2,5-dimethoxyphenylisopropylamine