Light-dark phase differences in behavioral effects of moclobemide in rats.

Effects of single and repeated administration of the MAO-A-inhibitor moclobemide (MOC) on the spontaneous locomotor activity and the locomotor hyper- and hypoactivity induced by d-amphetamine and clonidine, resp., in male Wistar rats were studied in both the light (L) and the dark (D) phase of the diurnal cycle (L:0700-1900 h). In the light phase, two hours after single administration, MOC (10 and 50 mg/kg po) increased the basal activity and a dose of 50 mg/kg decreased the exploratory and gross activities and enhanced the effects of amphetamine and clonidine. On the other hand, in the dark phase MOC (50 mg/kg) increased the gross activity and potentiated amphetamine hyperactivity. Only exploration was diminished to the same extent as in the light phase. After repeated administration MOC increased only the gross activity in the light phase. In the dark phase, however, MOC diminished exploration and potentiated the d-amphetamine hyperactivity. MOC, in both doses used, diminished food and water consumption and the body weight gain during the treatment period. These results demonstrate that MOC influences the behavior of rats in a phase-dependent manner after both single and repeated administration.