Perseverance of exploration in novel environments predicts morphine place conditioning in rats.
Reactivity to novelty has been related to operant drug self-administration but does not seem involved in the conditioned place preference (CPP). To further assess this issue our aims were to investigate: (1) the importance of the initial versus delayed activity in the novel environment to predict the CPP induced by morphine; (2) the separate contribution of trait anxiety in morphine CPP. Male Sprague-Dawley rats were exposed to a circular corridor for 30 min to assess reactivity to novelty and to the elevated plus-maze and the light-dark tests as measures of anxiety and morphine CPP was then studied (three pairings with 5 mg/kg s.c. morphine and three with saline). Delayed activity in the corridor (16-30 min) correlated positively with CPP score, whereas the initial activity (0-15 min) did not. High-responders (HR), those more active during the second half of the corridor, developed morphine CPP in contrast to low-responders (LR). Also, HR and LR did not differ in anxiety nor any plus-maze or light-dark test measure correlated with CPP behaviour. Enhanced vulnerability to develop morphine CPP is predicted by a higher delayed activity in a novel environment, regardless of anxiety.
Nadal
R
R
Institut de Neurociències, Unitat de Psicobiologia, Facultat de Psicologia, Universitat Autònoma de Barcelona, 08193 Bellaterra, Barcelona, Spain. roser.nadal@uab.es
Rotllant
D
D
Márquez
C
C
Armario
A
A
D000223:Adaptation, Psychological; D000704:Analysis of Variance; D000818:Animals; D001007:Anxiety / Q000139:chemically induced / Q000523:psychology; D001245:Association Learning / Q000187:drug effects*; D016739:Behavior, Addictive / Q000523:psychology; D003216:Conditioning, Operant / Q000187:drug effects*; D004777:Environment; D005106:Exploratory Behavior / Q000187:drug effects*; D008297:Male; D009020:Morphine / Q000008:administration & dosage*; D009043:Motor Activity / Q000187:drug effects; D009294:Narcotics / Q000008:administration & dosage; D011214:Practice, Psychological; D011237:Predictive Value of Tests; D051381:Rats; D017207:Rats, Sprague-Dawley; D012054:Reinforcement, Psychology; D018709:Statistics, Nonparametric
D009294:Narcotics; D009020:Morphine