title: Cocaine-induced CREB phosphorylation in nucleus accumbens of cocaine-sensitized rats is enabled by enhanced activation of extracellular signal-related kinase, but not protein kinase A.
abstract: Repeated cocaine administration to rats outside their home cages sensitizes the behavioral effects of the drug, and enhances induction of the immediate early gene product Fos in nucleus accumbens. We hypothesized that the same treatment regimen would also enhance cocaine-induced activation of intracellular signaling kinases that phosphorylate cyclic AMP-regulated element-binding protein (CREB), an important mediator of c-fos transcription. Phosphorylation levels of extracellular signal-regulated kinase (ERK)/mitogen-activated protein kinase (MAPK), calcium/calmodulin kinases (CaMKs) II and IV, and CREB were used to assess endogenous functional activity of these signaling molecules in rats behaviorally sensitized outside their home cages. Protein kinase A (PKA)-specific phosphorylation of Ser845 in the alpha-amino-3-hydroxy-5-methylisoxazole-4-propionate (AMPA) receptor subunit GluR1 was used to assess endogenous functional activity of PKA. Using western blots and immunohistochemistry, we detected cocaine-induced CREB phosphorylation after repeated cocaine administration, but not after repeated saline administration. Using western blots and MAPK activity assays, we found that cocaine-induced phosphorylation and activation of ERK, but not of CaMKs II or IV or GluR1, was augmented in nucleus accumbens of cocaine-sensitized rats. Unilateral infusions of the MAPK kinase inhibitor U0126 into nucleus accumbens attenuated cocaine-induced ERK and CREB phosphorylation in cocaine-sensitized rats. In contrast, unilateral infusions of the PKA inhibitor Rp-isomer of adenosine-3',5'-cyclicmonophosphorothioate (Rp-cAMPs) did not affect cocaine-induced CREB phosphorylation. Therefore, enhanced activation of ERK, but not PKA, enables and mediates cocaine-induced CREB phosphorylation in nucleus accumbens of rats that are sensitized by repeated cocaine administration outside their home cages.
authors.affiliation: Behavioral Neuroscience Branch, Intramural Research Program, National Institute on Drug Abuse, National Institutes of Health, Department of Health and Human Services, Baltimore, Maryland 21224, USA.
authors.forename: Brandi J
authors.initials: BJ
authors.lastname: Mattson
authors.forename: Jennifer M
authors.initials: JM
authors.lastname: Bossert
authors.forename: Danielle E
authors.initials: DE
authors.lastname: Simmons
authors.forename: Naohito
authors.initials: N
authors.lastname: Nozaki
authors.forename: Deepti
authors.initials: D
authors.lastname: Nagarkar
authors.forename: Justin D
authors.initials: JD
authors.lastname: Kreuter
authors.forename: Bruce T
authors.initials: BT
authors.lastname: Hope
mesh_terms: D000779:Anesthetics, Local / Q000008:administration & dosage*; D000818:Animals; D001522:Behavior, Animal; D015153:Blotting, Western / Q000379:methods; D050882:CREB-Binding Protein / Q000378:metabolism*; D002452:Cell Count / Q000379:methods; D003042:Cocaine / Q000008:administration & dosage*; D019970:Cocaine-Related Disorders / Q000378:metabolism*; D017868:Cyclic AMP-Dependent Protein Kinases / Q000378:metabolism; D004347:Drug Interactions; D004789:Enzyme Activation / Q000187:drug effects; D004791:Enzyme Inhibitors / Q000494:pharmacology; D048049:Extracellular Signal-Regulated MAP Kinases / Q000378:metabolism*; D007150:Immunohistochemistry / Q000379:methods; D008297:Male; D009043:Motor Activity / Q000187:drug effects; D009714:Nucleus Accumbens / Q000187:drug effects* / Q000201:enzymology / Q000378:metabolism; D010766:Phosphorylation / Q000187:drug effects; D051381:Rats; D017207:Rats, Sprague-Dawley; D013997:Time Factors
chemical_list: D000779:Anesthetics, Local; D004791:Enzyme Inhibitors; D050882:CREB-Binding Protein; D017868:Cyclic AMP-Dependent Protein Kinases; D048049:Extracellular Signal-Regulated MAP Kinases; D003042:Cocaine