title: Previous exposure to VTA amphetamine enhances cocaine self-administration under a progressive ratio schedule in an NMDA, AMPA/kainate, and metabotropic glutamate receptor-dependent manner.
abstract: Previous exposure to amphetamine (AMPH) in the ventral tegmental area (VTA) enhances cocaine self-administration in a D(1) dopamine receptor-dependent manner. The present study examined the contribution of VTA NMDA, AMPA/kainate, and metabotropic glutamate (mGlu) receptors to this effect. Rats in different groups received three intra-VTA injections, one every third day, of either saline (0.5 microl/side), AMPH (2.5 microg/0.5 microl/side), AMPH+CPP (NMDA receptor antagonist; 10 microM or 100 microM/0.5 microl/side), AMPH+CNQX (AMPA/kainate receptor antagonist; 0.3 mM or 1 mM/0.5 microl/side), AMPH+MCPG (mGlu receptor antagonist; 0.5 mM or 50 mM/0.5 microl/side), or the glutamate receptor antagonists alone. Starting 7-10 days after the last pre-exposure injection, rats were trained to self-administer cocaine (0.3 mg/kg/infusion) and then tested under a progressive ratio (PR) schedule of reinforcement for 6 consecutive days. As reported previously, VTA AMPH pre-exposed rats worked more and obtained more infusions of cocaine than saline pre-exposed animals. Coadministration of CPP, CNQX, or MCPG with AMPH during pre-exposure dose-dependently blocked this enhancement of cocaine self-administration. Rats pre-exposed to the glutamate receptor antagonists alone did not differ on the test days from the saline pre-exposed controls. These results indicate that, in a manner paralleling the induction of sensitization of the locomotor stimulating effects of AMPH, activation of NMDA, AMPA/kainate, and mGlu receptors during pre-exposure to AMPH in the VTA is necessary for the enhancement of cocaine self-administration to develop.
authors.affiliation: Department of Psychology, The University of Chicago, IL 60637, USA.
authors.forename: Nobuyoshi
authors.initials: N
authors.lastname: Suto
authors.forename: Lauren M
authors.initials: LM
authors.lastname: Tanabe
authors.forename: Jennifer D
authors.initials: JD
authors.lastname: Austin
authors.forename: Elizabeth
authors.initials: E
authors.lastname: Creekmore
authors.forename: Paul
authors.initials: P
authors.lastname: Vezina
mesh_terms: D000661:Amphetamine / Q000494:pharmacology*; D000818:Animals; D003042:Cocaine / Q000008:administration & dosage*; D008297:Male; D051381:Rats; D020318:Rats, Long-Evans; D018091:Receptors, AMPA / Q000819:agonists / Q000037:antagonists & inhibitors / Q000502:physiology; D017470:Receptors, Glutamate / Q000502:physiology*; D018092:Kainic Acid Receptors / Q000819:agonists / Q000037:antagonists & inhibitors / Q000502:physiology; D018094:Receptors, Metabotropic Glutamate / Q000819:agonists / Q000037:antagonists & inhibitors / Q000502:physiology; D016194:Receptors, N-Methyl-D-Aspartate / Q000819:agonists / Q000037:antagonists & inhibitors / Q000502:physiology; D012055:Reinforcement Schedule; D012646:Self Administration / Q000523:psychology; D017557:Ventral Tegmental Area / Q000187:drug effects* / Q000502:physiology
chemical_list: D000661:Amphetamine; D003042:Cocaine; D018091:Receptors, AMPA; D017470:Receptors, Glutamate; D018092:Kainic Acid Receptors; D018094:Receptors, Metabotropic Glutamate; D016194:Receptors, N-Methyl-D-Aspartate