Dissociations between interval timing and intertemporal choice following administration of fluoxetine, cocaine, or methamphetamine

Behav Processes. 2014 Jan;101:123-34. doi: 10.1016/j.beproc.2013.09.013. Epub 2013 Oct 14.

Abstract

The goal of our study was to characterize the relationship between intertemporal choice and interval timing, including determining how drugs that modulate brain serotonin and dopamine levels influence these two processes. In Experiment 1, rats were tested on a standard 40-s peak-interval procedure following administration of fluoxetine (3, 5, or 8 mg/kg) or vehicle to assess basic effects on interval timing. In Experiment 2, rats were tested in a novel behavioral paradigm intended to simultaneously examine interval timing and impulsivity. Rats performed a variant of the bi-peak procedure using 10-s and 40-s target durations with an additional "defection" lever that provided the possibility of a small, immediate reward. Timing functions remained relatively intact, and 'patience' across subjects correlated with peak times, indicating a negative relationship between 'patience' and clock speed. We next examined the effects of fluoxetine (5 mg/kg), cocaine (15 mg/kg), or methamphetamine (1 mg/kg) on task performance. Fluoxetine reduced impulsivity as measured by defection time without corresponding changes in clock speed. In contrast, cocaine and methamphetamine both increased impulsivity and clock speed. Thus, variations in timing may mediate intertemporal choice via dopaminergic inputs. However, a separate, serotonergic system can affect intertemporal choice without affecting interval timing directly. This article is part of a Special Issue entitled: Associative and Temporal Learning.

Keywords: Clock speed; Dopamine; Impulsivity; Self control; Serotonin; Temporal discounting.

Publication types

  • Research Support, N.I.H., Extramural

MeSH terms

  • Animals
  • Behavior, Animal / drug effects*
  • Choice Behavior / drug effects*
  • Cocaine / pharmacology*
  • Dopamine Uptake Inhibitors / pharmacology*
  • Fluoxetine / pharmacology*
  • Impulsive Behavior
  • Learning / drug effects
  • Methamphetamine / pharmacology*
  • Rats
  • Rats, Sprague-Dawley
  • Serotonin Uptake Inhibitors / pharmacology*
  • Time Perception / drug effects

Substances

  • Dopamine Uptake Inhibitors
  • Serotonin Uptake Inhibitors
  • Fluoxetine
  • Methamphetamine
  • Cocaine