THE EFFECT OF ANTIDEPRESSANT DRUGS ON THE ULTRADIAN RHYTHMS OF THE LOCOMOTOR-ACTIVITY IN RATS

The effect of two antidepressant drugs (+)- and (-)-oxaprotiline hydrochloride (Ciba-Geigy, OXA) on the exploration and the basal activity of rats in the light and dark phases of the diurnal cycle was investigated. (+)-OXA is a selective noradrenaline (NA) uptake inhibitor, while its (-)-enantiomer is devoid of such an activity. Male Wistar rats housed individually on a 12:12 h light-dark schedule (light on: 07.00 h) were treated with (+)- or (-)-OXA in a dose of 10 mg/kg twice daily, for 14 days. The rats received the last dose at the beginning of the light or dark phase and their movements were registered using Animex actometers for 12 h. The first 30 min of activity was regarded as the exploratory and the further period as the basal activity. In the light phase both (+)- and (-)-OXA decreased the exploration (80% and 70% of control, resp., p < 0.05) and potentiated it (180% and 190% of control, resp., p < 0.01) in the dark phase. The effect on the ultradian rhythm of the basal activity was phase-dependent also. (+)-OXA prolonged the period and did not change mesor, amplitude or acrophase of the rhythm in the light phase, and diminished mesor and amplitude, shifted acrophase and did not change period in the dark phase. (-)-OXA did not change parameters of the rhythm in the light phase and shortened period, diminished mesor and shifted acrophase of the rhythm in the dark phase. The results show that both (+)- and (-)-OXA given in the same dose change the same activity in opposite ways in the light and dark phases of the diurnal cycle. The NA uptake inhibition seems not to be a requisite of the light/dark phase differences.