Blockade of the anxiolytic action of 8-OH-DPAT in lactating rats

The anxiolytic action of 8-OH-DPAT (0.125, 0.5, and 0.75 mg/kg, IP, -15 min) was evaluated in ovariectomized and 7-day lactating mother rats. This serotonergic anxiolytic produces a clear reduction in cumulative burying behavior and in freezing time (parameters denoting a reduction in anxiety levels) in ovariectomized subjects. However, in 7-day lactating mother rats, 8-OH-DPAT lacked its antianxiety effects. Additionally, as an extra parameter of the animal's emotionality the number of defecation bolus was registered. A reduction in this parameter in ovariectomized animals after 8-OH-DPAT (0.5 mg/kg) injection was found. This effect was also blocked in 7-day lactating rats. None of the doses of the compound tested altered the burying behavior latency (a parameter inversely representing the animal's reactivity). The general ambulatory behavior of ovariectomized subjects was significantly impaired at the highest dose (0.75 mg/kg) of 8-OH-DPAT. Lower doses did not alter this parameter or the number of times lines are crossed (a parameter denoting exploratory activity). Discussion is focused on the relationship between the activity of the serotonergic system and the secretion of prolactin in this period.