title: Individual differences in cocaine-induced locomotor activity in rats: behavioral characteristics, cocaine pharmacokinetics, and the dopamine transporter.
abstract: Outbred male Sprague-Dawley rats can be classified as either low or high cocaine responders (LCRs or HCRs, respectively) based on their locomotor response to acute cocaine. Concomitant measurement of dopamine clearance in these rats revealed that the differential behavioral responses are associated with the magnitude of dopamine transporter (DAT) inhibition by cocaine. Here, we investigated several factors that might contribute to cocaine-induced behavioral variability and its association with differential inhibition of DAT function. In rats classified as LCRs or HCRs after 10 mg/kg cocaine injection, we found no differences in (1) novelty-induced locomotion, (2) cocaine levels in dorsal striatum or nucleus accumbens (NAc), (3) DAT number or affinity in NAc, or (4) DAT affinity for cocaine in NAc. In rats given 20 mg/kg cocaine, behavior was more uniform across individuals, but still warranted separation into LCR/HCR categories. Additionally, we analyzed the stability of the LCR/HCR classification made during the first test with 10 or 20 mg/kg cocaine by retesting rats 7 days later with saline or cocaine (10 or 20 mg/kg). Before injection, HCRs were more active relative to LCRs and to their own behavior on the first test day. Following cocaine, LCRs and HCRs exhibited similar drug-induced changes in locomotion, but there were unique effects that depended on the cocaine dose given on the first and second test days. Our results argue against several likely explanations for individual differences in cocaine-induced behavior and highlight the influence of a single cocaine exposure on subsequent behavioral responses to the drug.
authors.affiliation: Department of Pharmacology and Neuroscience Program, University of Colorado Health Sciences Center, Denver, CO 80262, USA. joshua.gulley@uchsc.edu
authors.forename: Joshua M
authors.initials: JM
authors.lastname: Gulley
authors.forename: Brian R
authors.initials: BR
authors.lastname: Hoover
authors.forename: Gaynor A
authors.initials: GA
authors.lastname: Larson
authors.forename: Nancy R
authors.initials: NR
authors.lastname: Zahniser
mesh_terms: D000818:Animals; D001665:Binding Sites / Q000187:drug effects; D001923:Brain Chemistry; D002851:Chromatography, High Pressure Liquid / Q000379:methods; D003042:Cocaine / Q000031:analogs & derivatives* / Q000493:pharmacokinetics* / Q000494:pharmacology; D003342:Corpus Striatum / Q000187:drug effects / Q000378:metabolism; D050483:Dopamine Plasma Membrane Transport Proteins; D018765:Dopamine Uptake Inhibitors / Q000493:pharmacokinetics / Q000494:pharmacology; D004305:Dose-Response Relationship, Drug; D005106:Exploratory Behavior / Q000502:physiology; D006257:Head / Q000502:physiology; D007206:Individuality; D008297:Male; D008562:Membrane Glycoproteins; D026901:Membrane Transport Proteins / Q000378:metabolism*; D009043:Motor Activity / Q000187:drug effects*; D009419:Nerve Tissue Proteins; D009714:Nucleus Accumbens / Q000187:drug effects / Q000378:metabolism; D011869:Radioligand Assay / Q000379:methods; D051381:Rats; D017207:Rats, Sprague-Dawley; D013239:Stereotyped Behavior; D013997:Time Factors
chemical_list: D050483:Dopamine Plasma Membrane Transport Proteins; D018765:Dopamine Uptake Inhibitors; D008562:Membrane Glycoproteins; D026901:Membrane Transport Proteins; D009419:Nerve Tissue Proteins; C493216:Slc6a3 protein, rat; C021279:(1R-(exo,exo))-3-(4-fluorophenyl)-8-methyl-8- azabicyclo(3.2.1)octane-2-carboxylic acid, methyl ester; D003042:Cocaine