Circulating prolactin, MPOA prolactin receptor expression and maternal aggression in lactating rats

Maternal aggression is most intense in lactating rats from the 3rd to the 12th day postpartum. The purpose of this study was to determine if plasma prolactin (PRL) and prolactin receptor (PRL-RL) mRNA expression in the medial preoptic area (MPOA) of lactating rats are altered in association with maternal aggression. Lactating Sprague Dawley rats were divided into five groups and exposed for 10 min to an intruder male or to an object on postpartum day 8. Trunk blood and the brain of the dams were collected 30 or 240 min after exposure and from a non-exposed group. Lower levels of prolactin were found 30 min after the aggression test. No change was detected in the number of cells expressing PRL-RL mRNA by in situ hybridization histochemistry (ISHH) as a function of testing. However, the correlation between plasma PRL and PRL-RL mRNA expression in the mothers changed from positive in control females to negative in intruder exposed animals. These data support the concept that a maternal aggressive experience, while acutely altering PRL secretion, fails to affect PRL-RL mRNA expression.