Chlordiazepoxide and dizocilpine, but not morphine, selectively impair acquisition under a novel repeated-acquisition and performance task in rats.
BACKGROUND
Some classes of drugs can selectively affect learning (i.e., acquisition of behavior) at doses that do not affect performance (i.e., previously learned behavior). Some drugs (e.g., benzodiazepines) show selective effects on acquisition across a wide variety of tasks. Other drugs [e.g., N-methyl-D-aspartate (NMDA) antagonists and opiate agonists], however, show selective effects under some tasks, but not others.


OBJECTIVE
The purpose of this study was to examine the effects of the NMDA-antagonist dizocilpine (0.01-0.3 mg/kg), the opiate-agonist morphine (1.0-17.0 mg/kg), and the benzodiazepine chlordiazepoxide (3.0-30.0 mg/kg) in rats under a novel repeated-acquisition and performance task.


METHODS
Nose pokes to a correct location within a 2x3 stimulus array on a computer touch screen were reinforced with food. In the acquisition component, the correct location changed across sessions but remained constant within sessions; in the performance component, the correct location was constant both across and within sessions.


RESULTS
Both chlordiazepoxide and dizocilpine selectively impaired accuracy in the acquisition component at doses that did not affect accuracy in the performance component or overall response speed. Morphine, however, did not affect acquisition without affecting performance or response speed.


CONCLUSIONS
These results with rats resembled those previously obtained for response-sequence learning in primates, rather than those previously reported for spatial learning in rats. Therefore, previous discrepancies in results for NMDA antagonists and opiate agonists across tasks probably were not a function of the species studied, but, rather, they more likely were a function of unique variables controlling acquisition within each task.
Pitts
R C
RC
Department of Psychology, University of North Carolina Wilmington, NC 28403-5612, USA. pittsr@uncw.edu
Buda
D R
DR
Keith
J R
JR
Cerutti
D T
DT
Galizio
M
M
D000818:Animals; D002707:Chlordiazepoxide / Q000494:pharmacology*; D003216:Conditioning, Operant / Q000187:drug effects*; D004193:Discrimination Learning / Q000187:drug effects; D016291:Dizocilpine Maleate / Q000494:pharmacology*; D004305:Dose-Response Relationship, Drug; D005247:Feeding Behavior / Q000187:drug effects; D008297:Male; D009020:Morphine / Q000494:pharmacology*; D011597:Psychomotor Performance / Q000187:drug effects*; D011619:Psychotropic Drugs / Q000494:pharmacology; D051381:Rats; D017207:Rats, Sprague-Dawley; D011930:Reaction Time / Q000187:drug effects; D012054:Reinforcement, Psychology
D011619:Psychotropic Drugs; D016291:Dizocilpine Maleate; D002707:Chlordiazepoxide; D009020:Morphine