Antidepressant-like effects of pregnancy and progesterone in Wistar rats as measured in the differential reinforcement of the low-rate 72 s task.
BACKGROUND
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.


OBJECTIVE
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.


OBJECTIVE
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.
Molina-Hernández
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Laboratorio de Conducta, Instituto de Investigaciones Psicológicas, Universidad Veracruzana, Veracruz, Mexico. mimoli@bugs.invest.uv.mx
Contreras
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Téllez-Alcántara
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D000818:Animals; D000928:Antidepressive Agents / Q000494:pharmacology*; D004305:Dose-Response Relationship, Drug; D005260:Female; D010052:Ovariectomy; D011247:Pregnancy; D011270:Pregnancy, Animal / Q000523:psychology*; D011374:Progesterone / Q000494:pharmacology*; D051381:Rats; D017208:Rats, Wistar; D012054:Reinforcement, Psychology
D000928:Antidepressive Agents; D011374:Progesterone