Artificial lighting conditions and melatonin alter motor performance in adult rats

• Published in: Neuroscience letters Vol. 280; no. 1; pp. 33 - 36
• Main Authors: Poulos, Stephen G., Borlongan, Cesario V.
• Format: Journal Article
• Language: English
• Published: Shannon Elsevier Ireland Ltd 11.02.2000; Elsevier
• Subjects: Animals; Biological and medical sciences; Biological clock; Circadian rhythm; Circadian Rhythm - drug effects; Circadian Rhythm - physiology; Darkness; Fundamental and applied biological sciences. Psychology; Hormones and neuropeptides. Regulation; Humans; Hypothalamus. Hypophysis. Epiphysis. Urophysis; Light; Lighting; Male; Melatonin - pharmacology; Motor Activity - drug effects; Motor Activity - physiology; Motor coordination; Nocturnal; Rats; Rats, Sprague-Dawley; Rotorod; Vertebrates: endocrinology; Biological clock; Rotorod; Motor coordination; Circadian rhythm; Light; Nocturnal; Locomotion; Vertebrata; Melatonin; Mammalia; Rat; Artificial lighting; Rodentia; Biological rhythm; Pineal hormone
• ISSN: 0304-3940; 1872-7972
• DOI: 10.1016/S0304-3940(99)00997-0

Entrained circadian rhythms may modulate many behavioral activities of animals and humans. In the present study, we examined whether lighting conditions and melatonin treatment participate behaviorally in the entrainment of circadian rhythms in the rodent. In experiment one, Sprague–Dawley rats were introduced to the Rotorod test apparatus at nighttime or daytime and either with the lights on (4 lux) or in the dark. During nighttime tests, the exposure of rats to dark or light condition did not alter mean rev./min or length of times spent on the Rotorod. Interestingly, during daytime tests, animals exposed to light condition displayed significantly reduced mean rev./min (7.95±1.68), as well as length of time on the Rotorod (41.07±3.45 s) compared with their performance in the dark condition (mean rev./min, 11.16±1.52; length of time spent on the Rotorod, 66.94±6.15 s). In experiment two, treatment with melatonin (1.5 mg/kg, orally administered at 1 h prior to testing) in animals introduced to the daytime test with exposure to light condition, restored the rev./min (12.90±1.26) and the time spent on the Rotorod (63.21± 2.73 s) to near normal levels. Thus, we demonstrated here that exposure of nocturnal animals to their preferred dark condition and treatment with melatonin could enhance motor coordination.