Locomotor activity: A distinctive index in morphine self-administration in rats

• Published in: PloS one 2017-04, Vol.12 (4), p.e0174272-e0174272
• Main Authors: Zhang, Jian-Jun, Kong, Qingyao
• Format: Article
• Language: English
• Subjects: Alcohol; Alcoholic beverages; Amphetamines; Amygdala; Analgesia; Analysis; Anesthesia; Animal behavior; Animal models; Animals; Attenuation; Audio equipment; Baclofen; Biology and Life Sciences; Biotechnology; Ca2+/calmodulin-dependent protein kinase II; Cages; Cannabinoid CB1 receptors; Chambers; Cocaine; Comparative analysis; Computer programs; Cues; Cytochrome; Cytochrome P450; Dendrites; Diamonds; Dietary restrictions; Dilution; Dopamine; Dopamine transporter; Drug abuse; Drug addiction; Drug-Seeking Behavior - physiology; Drugs; Endorphins; Ethanol; Extinction; Extinction, Psychological - physiology; Flushing; Genetic factors; Health aspects; Heroin; Illumination; Inhibition; Laboratories; Life sciences; Locomotion; Locomotion - drug effects; Locomotion - physiology; Locomotor activity; Male; Medical instruments; Medicine and Health Sciences; Mental disorders; Methamphetamine; Mice; Morphine; Morphine - pharmacology; Motor Activity - drug effects; Motor Activity - physiology; Narcotics; Nervous system; Neurobiology; Neurosciences; Nuclei; Pain perception; Pharmacological research; Pharmacology; Priming; Psychology; Psychopharmacology; Rats; Rats, Sprague-Dawley; Reinforcement (Psychology); Research and Analysis Methods; Rodents; Self Administration - methods; Side effects; Social Sciences; Sodium; Surgery; Training
• ISSN: 1932-6203; 1932-6203
• DOI: 10.1371/journal.pone.0174272

Self-administration of addictive drugs is a widely used tool for studying behavioral, neurobiological, and genetic factors in addiction. However, how locomotor activity is affected during self-administration of addictive drugs has not been extensively studied. In our present study, we tested the locomotor activity levels during acquisition, extinction and reinstatement of morphine self-administration in rats. We found that compared with saline self-administration (SA), rats that trained with morphine SA had higher locomotor activity. Rats that successfully acquired SA also showed higher locomotor activity than rats that failed in acquiring SA. Moreover, locomotor activity was correlated with the number of drug infusions but not with the number of inactive pokes. We also tested the locomotor activity in the extinction and the morphine-primed reinstatement session. Interestingly, we found that in the first extinction session, although the number of active pokes did not change, the locomotor activity was significantly lower than in the last acquisition session, and this decrease can be maintained for at least six days. Finally, morphine priming enhanced the locomotor activity during the reinstatement test, regardless of if the active pokes were significantly increased or not. Our results clearly suggest that locomotor activity, which may reflect the pharmacological effects of morphine, is different from drug seeking behavior and is a distinctive index in drug self-administration.