Effects of repeated treatment with antidepressant drugs on the 24 hour behavior in the light-dark synchronized mice.

Imipramine, amitriptyline, citalopram, zimelidine and mianserin--antidepressant drugs with a different mechanism of pharmacological activity, as well as haloperidol, a neuroleptic, and diazepam, an anxiolytic, administered for 14 days, were examined in photoresistor actometers in the exploratory activity test (within the first 60 min) and in the basic locomotor activity test (the following 11 h) in the light and dark phases of the LD 12:12 cycle. Imipramine had no effect on the exploratory activity in either phase of the cycle, yet it enhanced the basic locomotor activity in the light phase. Amitriptyline stimulated only the exploratory activity in the dark phase. Citalopram enhanced the exploratory activity in both phases and did not change the basic locomotor activity in either phase of the cycle. Zimelidine increased the exploratory activity in the dark phase and inhibited the basic locomotor activity in both phases. Mianserin stimulated the exploratory activity in the dark phase and the basic locomotor activity in the light one, yet it inhibited the latter in the dark phase. Haloperidol attenuated the exploratory activity in both phases and the basic locomotor activity in the light phase. Diazepam enhanced the exploratory activity in both phases, exerting no effect on the basic locomotor activity. The results indicate that the examined antidepressant drugs administered repeatedly exert a diversified effect on the exploratory activity and the basic locomotor activity in the dark and light phases, yet the dominating feature is the increased exploratory activity in the dark phase.