ENDOCRINE COMMUNICATION BETWEEN CONCEPTUS AND MOTHER - PLACENTAL-LACTOGEN STIMULATION OF MATERNAL-BEHAVIOR

The possible role of the conceptus in stimulating the onset of materna l behavior through its secretion of placental lactogens and their pass age into the brain was investigated in female rats. In the first study , significant mitogenic activity in the Nb-2 lymphoma cell bioassay wa s detected in cerebrospinal fluid (CSF) samples collected by push-pull perfusion from rats on days 12-21 of pregnancy, coincident with the e stablishment of placental function. In contrast, mitogenic activity wa s absent from CSF in lactating and gonadectomized, virgin females. In a second study the mitogenic activity in day 12 pregnant samples was n eutralized 71% with antibodies to rat placental lactogen-I (rPL-I) and >90% with a combination of antibodies to rPL-I plus rPL-II. In contra st, activity on day 21 of pregnancy, 1 day prepartum, was reduced by a ntibodies to rPL-II (>85%), but not by antibodies to rPL-I, indicating that the predominant lactogen in the CSF prepartum is rPL-II. The beh avioral actions of placental secretions were assessed in the third exp eriment by infusing recombinant rPL-I and purified rPL-II directly int o the medial preoptic area of the brain of steroid-primed, nulliparous rats. Latencies to respond maternally to foster young were significan tly reduced in rPL-I- and rPL-II-treated rats (2- to 3-day latencies) when compared with latencies in control females (5- to 6-day latencies ). Thus, the conceptus through its secretion of rPLs which apparently gain access to the CSF helps to prime the pregnant female's brain to r espond maternally at the end of gestation. This endocrine communicatio n between the developing conceptus and pregnant female appears to be a n important part of the biological system which helps to establish suc cessful maternal care.