Role of corticosterone in intravenous cocaine self-administration in rats.
The role of corticosterone in cocaine reinforcement was investigated in rats exposed to either response-contingent electric footshock, noncontingent shock or no shock prior to the initiation of testing for intravenous cocaine self-administration. Although rats from the two shock groups were consistently more sensitive to cocaine, plasma corticosterone was always significantly higher in all rats that subsequently self-administered low doses of cocaine compared to the rats that did not, regardless of the treatment condition. In fact, plasma corticosterone was always greater than approximately 150 ng/ml for rats that self-administered low doses of cocaine, suggesting that this stress hormone must be increased above a critical threshold for stable low-dose cocaine self-administration to subsequently occur. Plasma corticosterone was also measured following exposure to cocaine and was significantly elevated in rats from all three treatment groups during cocaine self-administration, provided that doses of cocaine that would maintain responding were tested. When the dose would not maintain self-administration, plasma corticosterone was markedly lower, suggesting that at higher concentrations, the cocaine injections alone were sufficient to increase plasma corticosterone above a critical threshold, even for rats which had low precocaine levels of the hormone. These data suggest a significant role for corticosterone in both the acquisition and maintenance of cocaine reinforcement in rats.
Goeders
N E
NE
Department of Pharmacology and Therapeutics, Louisiana State University Medical Center, Shreveport 71130-3932, USA.
Guerin
G F
GF
D000818:Animals; D003042:Cocaine / Q000008:administration & dosage*; D003345:Corticosterone / Q000097:blood / Q000502:physiology*; D007275:Injections, Intravenous; D008297:Male; D009043:Motor Activity / Q000187:drug effects; D051381:Rats; D017208:Rats, Wistar; D012044:Regression Analysis; D012054:Reinforcement, Psychology; D012646:Self Administration
D003042:Cocaine; D003345:Corticosterone