Influence of a conditioned light stimulus on cocaine self-administration in rats.
BACKGROUND
A number of studies have suggested that the continued presentation of stimuli associated with cocaine may contribute to drug-seeking and drug-taking. The influence of conditioned stimuli on the maintenance of self-administration has not, however, been systematically investigated.


OBJECTIVE
This study was designed to determine whether omission of a stimulus that had been paired with self-administered cocaine would influence the maintenance of cocaine self-administration and whether the effect was dependent on cocaine dose or session length.


METHODS
During self-administration training, self-administered cocaine infusions were always paired with the illumination of a light. On test days, self-administered cocaine was delivered either with or without the cocaine-associated cue. For one group of rats, responding maintained by cocaine (0.50 mg/kg per infusion) was measured during daily 18-h sessions. For other groups, responding maintained by additional doses of cocaine (0.125, 0.25, or 1.0 mg/kg per infusion) was measured during daily 8-h sessions. For a final group, daily test sessions (4-5 h) produced the dose-effect curve (0.015-1.0 mg/kg per infusion) by repeatedly reducing the cocaine dose from a starting dose of 1.0 mg/kg per infusion.


RESULTS
Removal of the light cue decreased cocaine self-administration. The magnitude of this effect was dependent on the dose of self-administered cocaine and on the test session duration. Greater decrements in responding were produced as session length increased or when low doses of cocaine were self-administered.


CONCLUSIONS
These findings demonstrate that in the absence of a cocaine-associated stimulus, cocaine self-administration is attenuated and that maintenance of cocaine self-administration is maximally affected by the presence or absence of the conditioned stimulus when the self-administered dose is low and/or when session duration is long.
Schenk
S
S
School of Psychology, Te Kura Maatai Hinengaro, Victoria University of Wellington, P.O. Box 600, Wellington, New Zealand. Susan.Schenk@vuw.ac.nz
Partridge
B
B
D000818:Animals; D003042:Cocaine / Q000008:administration & dosage* / Q000494:pharmacology; D003213:Conditioning, Psychological / Q000187:drug effects* / Q000502:physiology; D018765:Dopamine Uptake Inhibitors / Q000008:administration & dosage* / Q000494:pharmacology; D004305:Dose-Response Relationship, Drug; D008297:Male; D010775:Photic Stimulation / Q000379:methods; D051381:Rats; D017207:Rats, Sprague-Dawley; D011930:Reaction Time / Q000187:drug effects* / Q000502:physiology; D012646:Self Administration
D018765:Dopamine Uptake Inhibitors; D003042:Cocaine