RATIONALE: In rats, several behavioral changes occurring during pregnancy could be due to the presence of progesterone; some of them may be analyzed in the differential reinforcement of the low-rate 72 s task (DRL-72 s), which is designed for testing the antidepressant profile of drugs. OBJECTIVES: The aim of the present study was to analyze the behavior of pregnant rats or ovariectomized rats receiving exogenous progesterone in the DRL-72 s task. HYPOTHESIS: During pregnancy, rats will obtain a high number of reinforcers in the DRL-72 s task. METHODS: Pregnant rats or rats after delivery were tested in the DRL-72 s task at the 3rd, 7th, 14th, 17th, and 20th days. Control rats previously trained in the DRL-72 s task were ovariectomized; after recuperation, they received saline (0.9%, i.p.), clomipramine (1.25 mg/kg, i.p.), or desipramine (2.14 mg/kg, i.p.) for 28 days, and they were tested in the DRL-72 s task. In a second series of experiments, ovariectomized rats received vehicle or progesterone (0.5, 1.0, 2.0, 4.0 mg/kg, s.c.), and they were submitted to the DRL-72 s task. Locomotion was evaluated in the open field test. RESULTS: Pregnant rats tested at the 14th and 17th day and ovariectomized rats receiving progesterone or two tricyclic antidepressants obtained a higher number of reinforcers and a cohesive rightward shift in inter-response time distributions than those rats evaluated after delivery in the DRL-72 s task. A lower locomotion was observed only at the end of pregnancy. CONCLUSIONS: Antidepressant-like effects of pregnancy and progesterone were found in Wistar rats as measured in the DRL-72 s task.
RATIONALE: In rats, several behavioral changes occurring during pregnancy could be due to the presence of progesterone; some of them may be analyzed in the differential reinforcement of the low-rate 72 s task (DRL-72 s), which is designed for testing the antidepressant profile of drugs. OBJECTIVES: The aim of the present study was to analyze the behavior of pregnant rats or ovariectomized rats receiving exogenous progesterone in the DRL-72 s task. HYPOTHESIS: During pregnancy, rats will obtain a high number of reinforcers in the DRL-72 s task. METHODS: Pregnant rats or rats after delivery were tested in the DRL-72 s task at the 3rd, 7th, 14th, 17th, and 20th days. Control rats previously trained in the DRL-72 s task were ovariectomized; after recuperation, they received saline (0.9%, i.p.), clomipramine (1.25 mg/kg, i.p.), or desipramine (2.14 mg/kg, i.p.) for 28 days, and they were tested in the DRL-72 s task. In a second series of experiments, ovariectomized rats received vehicle or progesterone (0.5, 1.0, 2.0, 4.0 mg/kg, s.c.), and they were submitted to the DRL-72 s task. Locomotion was evaluated in the open field test. RESULTS: Pregnant rats tested at the 14th and 17th day and ovariectomized rats receiving progesterone or two tricyclic antidepressants obtained a higher number of reinforcers and a cohesive rightward shift in inter-response time distributions than those rats evaluated after delivery in the DRL-72 s task. A lower locomotion was observed only at the end of pregnancy. CONCLUSIONS: Antidepressant-like effects of pregnancy and progesterone were found in Wistar rats as measured in the DRL-72 s task.