title: Morphine treatment during pregnancy modulates behavioral selection in lactating rats.
abstract: Previous studies have demonstrated that treatment of postpartum female rats with morphine inhibits maternal behavior and stimulates foraging. Exposure to drugs of abuse may result in a progressive enhancement of their reinforcing effects. Puerperal treatment with morphine leads to reverse tolerance to this drug. The present study investigated whether repeated morphine treatment during late pregnancy may influence the effects of different morphine dosages on behavioral selection in lactating rats. Females were simultaneously exposed to pups and insects, and the choice between taking care of the pups and hunting insects was observed. Female Wistar rats were treated with morphine (3.5 mg/kg/day, subcutaneous [s.c.]) or saline for 5 days beginning on pregnancy day 17. On day 5 of lactation, animals were acutely challenged with morphine (0.5, 1.0, or 1.5 mg/kg, s.c.; MM0.5, MM1.0, and MM1.5 groups, respectively) or saline (MS group) and tested for predatory hunting and maternal behavior. Control groups were pretreated with saline and challenged with morphine (SM0.5, SM1.0, and SM1.5 groups) or saline (SS group). Animals treated with morphine during late pregnancy and acutely challenged with 1.0 mg/kg morphine (MM1.0 group) exhibited significantly decreased maternal behavior and enhanced hunting. This effect was not evident with the 0.5 mg/kg dose. The 1.5 mg/kg morphine dose decreased maternal behavior and increased hunting in both the MM1.5 group and in animals challenged with morphine after previous saline treatment (SM1.5 group). These results provide evidence of plasticity of the opioidergic role in behavioral selection during lactation.
authors.affiliation: Departamento de Patologia, Faculdade de Medicina Veterinária e Zootecnia, Universidade de São Paulo, Av. Prof. Dr. Orlando Marques de Paiva, 87, Cidade Universitária, São Paulo SP, CEP 05588-000, Brasil. melloap@gmail.com
authors.forename: Aline de Mello
authors.initials: Ade M
authors.lastname: Cruz
authors.forename: Paulo C
authors.initials: PC
authors.lastname: Maiorka
authors.forename: Newton S
authors.initials: NS
authors.lastname: Canteras
authors.forename: Marcia H
authors.initials: MH
authors.lastname: Sukikara
authors.forename: Luciano F
authors.initials: LF
authors.lastname: Felicio
mesh_terms: D000222:Adaptation, Physiological / Q000187:drug effects; D000818:Animals; D001522:Behavior, Animal / Q000187:drug effects*; D004305:Dose-Response Relationship, Drug; D004334:Drug Administration Schedule; D004361:Drug Tolerance; D005260:Female; D007774:Lactation; D008425:Maternal Behavior / Q000187:drug effects*; D009020:Morphine / Q000008:administration & dosage*; D009294:Narcotics / Q000008:administration & dosage*; D009433:Neural Inhibition / Q000187:drug effects; D011235:Predatory Behavior / Q000187:drug effects*; D011247:Pregnancy; D051381:Rats; D017208:Rats, Wistar; D013997:Time Factors
chemical_list: D009294:Narcotics; D009020:Morphine