Artificial lighting conditions and melatonin alter motor performance in adult rats

Entrained circadian rhythms may modulate many behavioral: activities of ani mals and humans. In the present study, we examined whether lighting conditi ons and melatonin treatment participate behaviorally in the entrainment of circadian rhythms in the rodent. In experiment one, Sprague-Dawley:rats wer e introduced to the Rotorod test apparatus at nighttime or daytime and eith er with the lights on (4 lux) or in the dark. During nighttime tests, the e xposure of rats to dark or I ig ht condition did not a Iter mean rev./min o r length of times spent on the Rotorod. Interestingly, du ri ng daytime tes ts, animals exposed to light condition displayed significantly reduced mean rev./min (7.95 +/- 1.68), as well as length of rime 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 administ ered at 1 h prior to testing) in animals introduced to the daytime test wit h exposure to light condition, restored the rev./min (12.90 +/- 1.26) and t he 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 preferre d dark condition and treatment with melatonin could enhance motor coordinat ion. Published by Elsevier Science Ireland Ltd.