title: Effects of Group I metabotropic glutamate receptor antagonists on sensitivity to reinforcer magnitude and delayed reinforcement in a delay-discounting task in rats: Contribution of delay presentation order.
abstract: Metabotropic glutamate receptor 1 (mGluR1) blockade has been shown to decrease impulsive choice, as measured in delay discounting. However, several variables are known to influence an animal's discounting, including sensitivity to delayed reinforcement and sensitivity to reinforcer magnitude. The goal of this experiment was to determine the effects of mGluR1, as well as mGluR5, antagonism on these parameters. Forty Sprague Dawley rats were trained in delay discounting, in which consistently choosing a small, immediate reward reflects impulsive choice. For half of the rats, the delay to the large reinforcer increased across blocks of trials, whereas the delay decreased across the session for half of the rats. Following training, half of the rats received injections of the mGluR1antagonist JNJ 16259685 (JNJ; 0, 0.1, 0.3, or 1.0mg/kg; i.p), and half received injections of the mGluR5antagonist MPEP (0, 1.0, 3.0, or 10.0mg/kg; i.p.). Administration of JNJ increased sensitivity to delayed reinforcement (i.e., promoted impulsive choice), regardless of which schedule was used. However, the order in which delays were presented modulated the effects of JNJ on sensitivity to reinforcer magnitude. Specifically, JNJ decreased sensitivity to reinforcer magnitude in rats trained on the descending schedule only. MPEP did not alter sensitivity to reinforcer magnitude or sensitivity to delayed reinforcement. These results show that mGluR1is an important mediator of impulsive choice, and they provide further evidence that delay order presentation is an important variable that influences drug effects in delay discounting.
authors.affiliation: Department of Psychological Science, Northern Kentucky University, USA. Electronic address: yatesj1@nku.edu.
authors.forename: Justin R
authors.initials: JR
authors.lastname: Yates
authors.affiliation: Department of Psychological Science, Northern Kentucky University, USA.
authors.forename: Katherine K
authors.initials: KK
authors.lastname: Rogers
authors.affiliation: Department of Psychological Science, Northern Kentucky University, USA.
authors.forename: Benjamin T
authors.initials: BT
authors.lastname: Gunkel
authors.affiliation: Department of Psychological Science, Northern Kentucky University, USA.
authors.forename: Nicholas A
authors.initials: NA
authors.lastname: Prior
authors.affiliation: Department of Psychological Science, Northern Kentucky University, USA.
authors.forename: Mallory N
authors.initials: MN
authors.lastname: Hughes
authors.affiliation: Department of Psychological Science, Northern Kentucky University, USA.
authors.forename: Sara M
authors.initials: SM
authors.lastname: Sharpe
authors.affiliation: Department of Psychological Science, Northern Kentucky University, USA.
authors.forename: Hunter L
authors.initials: HL
authors.lastname: Campbell
authors.affiliation: Department of Psychological Science, Northern Kentucky University, USA.
authors.forename: Anthony B
authors.initials: AB
authors.lastname: Johnson
authors.affiliation: Department of Psychological Science, Northern Kentucky University, USA.
authors.forename: Margaret G
authors.initials: MG
authors.lastname: Keller
authors.affiliation: Department of Psychological Science, Northern Kentucky University, USA.
authors.forename: Kerry A
authors.initials: KA
authors.lastname: Breitenstein
authors.affiliation: Department of Psychological Science, Northern Kentucky University, USA.
authors.forename: Hansen N
authors.initials: HN
authors.lastname: Shults
mesh_terms: D000704:Analysis of Variance; D000818:Animals; D065786:Delay Discounting / Q000187:drug effects* / Q000502:physiology; D004305:Dose-Response Relationship, Drug; D018691:Excitatory Amino Acid Antagonists / Q000494:pharmacology*; D007175:Impulsive Behavior / Q000187:drug effects / Q000502:physiology; D008297:Male; D011581:Psychological Tests; D011725:Pyridines / Q000494:pharmacology; D011804:Quinolines / Q000494:pharmacology*; D017207:Rats, Sprague-Dawley; D064529:Receptor, Metabotropic Glutamate 5 / Q000037:antagonists & inhibitors / Q000378:metabolism; D018094:Receptors, Metabotropic Glutamate / Q000037:antagonists & inhibitors* / Q000378:metabolism; D012054:Reinforcement, Psychology
chemical_list: C495417:(3,4-dihydro-2H-pyrano(2,3)b-quinolin-7-yl)-(cis-4-methoxycyclohexyl) methanone; D018691:Excitatory Amino Acid Antagonists; C578937:Grm5 protein, rat; D011725:Pyridines; D011804:Quinolines; D064529:Receptor, Metabotropic Glutamate 5; D018094:Receptors, Metabotropic Glutamate; C104077:metabotropic glutamate receptor type 1; C121465:6-methyl-2-(phenylethynyl)pyridine
keywords: Delay discounting; Impulsive choice; Metabotropic glutamate receptor; Rat; Sensitivity to delayed reinforcement; Sensitivity to reinforcer magnitude