Discrimination of circadian phase in intact and suprachiasmatic nuclei-ablated rats.
This study examined whether the circadian system of rats can serve as a consulted clock for discriminating time of day. Food restricted rats housed in activity wheels were trained to lever press for food in a two-lever T-maze in which the left arm was correct in a morning feeding session, and the right arm in an afternoon session (7 h interval). All six rats learned the task (discrimination ratios > chance on 85-95% of sessions) and exhibited anticipatory wheel running prior to most sessions. Performance was not disrupted by inverting the LD cycle or by omitting 1-3 sessions, indicating that learning was not dependent on light-dark cues, alternation strategies, or physiological states associated with intermeal interval. Five of six additional rats with ablations of the suprachiasmatic nucleus light-entrainable pacemaker acquired the discrimination, indicating that time-of-day cues can be provided by another circadian pacemaker (likely food-entrainable). The results provide the first clear evidence that the circadian system in a mammal can function as a consulted clock that provides discriminative time cues for cognitive processes subserving behavioral plasticity.
Mistlberger
R E
RE
Department of Psychology, Simon Fraser University, Burnaby, B.C, Canada. mistlber@sfu.ca
de Groot
M H
MH
Bossert
J M
JM
Marchant
E G
EG
D000818:Animals; D001683:Biological Clocks / Q000502:physiology*; D002940:Circadian Rhythm / Q000502:physiology*; D003216:Conditioning, Operant / Q000502:physiology*; D004193:Discrimination Learning / Q000502:physiology*; D005508:Food Deprivation / Q000502:physiology; D008297:Male; D018782:Maze Learning / Q000502:physiology*; D005082:Physical Exertion / Q000502:physiology; D051381:Rats; D017208:Rats, Wistar; D012016:Reference Values; D012420:Running / Q000502:physiology; D013493:Suprachiasmatic Nucleus / Q000502:physiology*