title: Molecular neuroadaptations in the accumbens and ventral tegmental area during the first 90 days of forced abstinence from cocaine self-administration in rats.
abstract: Cocaine self-administration is associated with a propensity to relapse in humans and reinstatement of drug seeking in rats after prolonged withdrawal periods. These behaviors are hypothesized to be mediated by molecular neuroadaptations within the mesolimbic dopamine system. However, in most studies of drug-induced neuroadaptations, cocaine was experimenter-delivered and molecular measurements were performed after short withdrawal periods. In the present study, rats were trained to self-administer intravenous cocaine or oral sucrose (a control non-drug reward) for 10 days (6-h/day) and were killed following 1, 30, or 90 days of reward withdrawal. Tissues from the accumbens and ventral tegmental area (VTA) were assayed for candidate molecular neuroadaptations, including enzyme activities of cAMP-dependent protein kinase (PKA) and adenylate cyclase (AC), and protein expression of cyclin-dependent kinase 5 (cdk5), tyrosine hydroxylase (TH) and glutamate receptor subunits (GluR1, GluR2 and NMDAR1). In the accumbens of cocaine-trained rats, GluR1 and NMDAR1 levels were increased on days 1 and 90, while GluR2 levels were increased on days 1 and 30, but not day 90; PKA activity levels were increased on days 1 and 30, but not day 90, while AC activity, TH and cdk5 levels were unaltered. In the VTA of cocaine-trained rats, NMDAR1 levels were increased for up to 90 days, while GluR2 levels were increased only on day 1; TH and Cdk5 levels were increased only on day 1, while PKA and AC activity levels were unaltered. Cocaine self-administration produces long-lasting molecular neuroadaptations in the VTA and accumbens that may underlie cocaine relapse during periods of abstinence.
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: Lin
authors.initials: L
authors.lastname: Lu
authors.forename: Jeff W
authors.initials: JW
authors.lastname: Grimm
authors.forename: Yavin
authors.initials: Y
authors.lastname: Shaham
authors.forename: Bruce T
authors.initials: BT
authors.lastname: Hope
mesh_terms: D000222:Adaptation, Physiological / Q000187:drug effects; D000262:Adenylyl Cyclases / Q000378:metabolism; D000818:Animals; D015153:Blotting, Western; D003042:Cocaine / Q000008:administration & dosage* / Q000009:adverse effects; D019970:Cocaine-Related Disorders / Q000378:metabolism*; D017868:Cyclic AMP-Dependent Protein Kinases / Q000378:metabolism; D051360:Cyclin-Dependent Kinase 5; D018844:Cyclin-Dependent Kinases / Q000378:metabolism; D004195:Disease Models, Animal; D008297:Male; D009714:Nucleus Accumbens / Q000187:drug effects / Q000378:metabolism*; D051381:Rats; D020318:Rats, Long-Evans; D018091:Receptors, AMPA / Q000378:metabolism; D016194:Receptors, N-Methyl-D-Aspartate / Q000378:metabolism; D012646:Self Administration; D013375:Substance Withdrawal Syndrome / Q000378:metabolism*; D013997:Time Factors; D014446:Tyrosine 3-Monooxygenase / Q000378:metabolism; D017557:Ventral Tegmental Area / Q000378:metabolism*
chemical_list: D000262:Adenylyl Cyclases; D003042:Cocaine; D017868:Cyclic AMP-Dependent Protein Kinases; D051360:Cyclin-Dependent Kinase 5; D018844:Cyclin-Dependent Kinases; D018091:Receptors, AMPA; D016194:Receptors, N-Methyl-D-Aspartate; D014446:Tyrosine 3-Monooxygenase; C409466:NR1 NMDA receptor; C495907:Cdk5 protein, rat; C104722:glutamate receptor ionotropic, AMPA 2