Variability of drug self-administration in rats.
BACKGROUND
Although temporal patterns of drug self-administration in animals are known to be highly regular, this regularity has rarely been quantified or systematically compared across reinforcers.


OBJECTIVE
Over a range of unit doses, this study assessed: (1) the within-subject variability of inter-infusion intervals (latencies); (2) the estimated whole-body drug level at the time of self-infusion; (3) the within-subject variability of these drug levels; and (4) the statistical dependence between successive latencies, to determine whether regularity is maintained by compensatory, moment-to-moment adjustment of latencies.


METHODS
Rats were trained with cocaine (10-1000 microg/kg per infusion, IV), remifentanil (an ultra-short acting opioid; 0.25-32 microg/kg per infusion, IV), or food (20-180 mg/delivery).


RESULTS
Within subjects, latencies were most consistent from infusion to infusion at unit doses on the descending limb of the dose-response curve. However, the drug level at the time an infusion was initiated was actually least consistent at these doses. Sequential latencies showed only a weak autocorrelation for both drugs.


CONCLUSIONS
These results suggest that highly consistent response patterns are not simply a product of precise titration of drug levels. The weak autocorrelation between sequential latencies suggests that temporal regularity of responding is not maintained through compensatory adjustments of post-infusion pauses.
Panlilio
Leigh V
LV
Preclinical Pharmacology Section, Behavioral Neuroscience Branch, Intramural Research Program, National Institute on Drug Abuse, 5500 Nathan Shock Drive, Baltimore, MD 21224, USA. lpanlili@intra.nida.nih.gov
Katz
Jonathan L
JL
Pickens
Roy W
RW
Schindler
Charles W
CW
D000701:Analgesics, Opioid / Q000008:administration & dosage / Q000494:pharmacology*; D000818:Animals; D003042:Cocaine / Q000008:administration & dosage / Q000494:pharmacology*; D003216:Conditioning, Operant; D004305:Dose-Response Relationship, Drug; D005502:Food; D008297:Male; D010880:Piperidines / Q000008:administration & dosage / Q000494:pharmacology*; D051381:Rats; D017207:Rats, Sprague-Dawley; D011930:Reaction Time; D012055:Reinforcement Schedule; D000077208:Remifentanil; D012646:Self Administration
D000701:Analgesics, Opioid; D010880:Piperidines; D003042:Cocaine; D000077208:Remifentanil