Effect of Ethanol and Theophylline on Circadian Rhythm of Rat Locomotion

The effect of ethanol and theophylline on the circadian rhythm of rat locomotion was investigated. Male Wistar rats synchronized to 12: 12 h light-dark cycles were divided into four groups for treatment with saline, ethanol, theophylline, and ethanol plus theophylline. Animals in each group were orally administered saline, ethanol (2.0 g/kg body wt), theophylline (10 mg/kg body wt), and ethanol plus theophylline, respectively, six times every 2 h during the 12-h light span. Spontaneous loco-motor activity was continuously monitored by an animal activity recorder at 15-min intervals. Total activity count, circadian rhythm characteristics of activity (amplitude, acrophase, and mesor), power spectral patterns, and slope of fluctuation (a measurement of ultradian periodicity) were calculated. Ethanol administration decreased the total activity count by 60% and phase-delayed the onset of activity rhythm by 9.5 h on the day after treatment. The absolute value of the slope of fluctuation was increased by ethanol administration. The mean recovery time evaluated by rhythm detection was 3.8 days. Theophylline administration increased the light phase activity, but caused no phase delay of the onset time of the locomotor activity rhythm. The decrease in total activity count and phase delay of onset of the activity rhythm caused by ethanol were partially antagonized by theophylline. However, the prolonged effects of ethanol, represented by a late recovery time and an increase in the slope of fluctuation, were not influenced by theophylline.