Rat placental lactogen-I binds to the choroid plexus and hypothalamus of the pregnant rat

Abstract

Recent findings suggest that placental lactogen has a role in the regulation of hypothalamic function during pregnancy. To explore the mechanisms by which placental hormones may exert effects in the maternal central nervous system, we have examined the binding of rat placental lactogen-I (rPL-I) to brain slices from pregnant rats at mid- and late gestation. The binding of rPL-I to maternal rat brain was compared with that of human GH (hGH). Radiolabelled rPL-I bound specifically to ependymal cells of the choroid plexus in the lateral ventricles and in the roof of the third ventricle. The binding of 125I-labelled rPL-I was inhibited by unlabelled rPL-I, hGH or rat prolactin but not by rat GH, indicating that rPL-I and rat prolactin interact with a common binding site in maternal rat brain. Radiolabelled hGH bound to the choroid plexus and to ependymal cells lining the third ventricle in the region of the arcuate nucleus. In addition, hGH bound specifically to the ventromedial nuclei and to the medial preoptic area of the hypothalamus. The binding of radiolabelled hGH to all brain regions was inhibited by unlabelled rPL-I as well as hGH, indicating that rPL-I competes for lactogenic binding sites in the hypothalamus as well as the choroid plexus of the pregnant rat. These findings suggest potential mechanisms by which placental hormones may exert direct effects on the maternal central nervous system during pregnancy. The precise functions and roles of the PL-I binding sites in maternal choroid plexus and hypothalamus remain to be explored.

Atlas of the neurons that express mRNA for the long form of the prolactin receptor in the forebrain of the female rat

“…The binding data are still somewhat complicated by the substantial binding of prolactin/growth hormone to several members of the growth hormone/ prolactin receptor superfamily. Interesting recent data on the binding of lactogenic ligands related to prolactin to the prolactin receptor suggest that other ligands prominent in pregnancy are also likely to interact importantly with this superfamily of receptors Kelly et al, 1991;Pihoker et al, 1993).…”

Endocrine Communication between Conceptus and Mother: Placental Lactogen Stimulation of Maternal Behavior

“…PRL as well as rPL-I appear to bind to epi thelial cells of the choroid plexus; their binding can be blocked by the addition of excess lactogenic hormones [8,22,23], Once in the CSF and past the blood-CSF barrier, rPL-I and rPL-II can simply diffuse into neuropil adjacent to or near the ventricles, e.g. the MPOA.…”

“…While it is unknown whether rPLs act at neural sites other than the MPOA to affect maternal behavior, the actions of rPLs after MPOA infu sions are probably not due to the diffusion of rPLs to oth er areas of the brain. Similar doses of oPRL which stimu late maternal behavior when infused into the MPOA do not affect maternal behavior when infused into the ven tricular system [3], Other support for the MPOA as a site of rPL action is the recent work of Pihoker et al [8] who reported in vitro binding of radiolabeled rPL-I to the MPOA, hypothalamus, and choroid plexus. Interestingly, the region of the MPOA which appeared maximally responsive to rPL-I and rPL-II stimulation of maternal behavior in the present study was at 7.8 to 8.0 in the AP plane.…”

“…placental lactogens. In rats, circulating placental lactogen concentrations are high during the second half of pregnancy [4,5], and rat placental lactogen-II (rPL-II) has been detected in the cerebrospinal fluid (CSF) of day 18 pregnant rats [6], The presence of placental lactogens in CSF in the rat is consis tent with studies in women in which human placental lac togen (hPL) was found in high concentrations in the CSF during gestation [7], A possible central action of placental lactogens in maternal behavior is supported by the Find ings that rPL-I and rPL-II bind to lactogenic receptors in the maternal choroid plexus and hypothalamus [8,9] and infusions of hPL into the MPOA of steroid-primed, nul liparous female rats stimulate a fast onset of maternal responsiveness [10], Thus, it appears that the developing conceptus through its secretion of placental lactogens may help prime the pregnant female so that she behaves mater nally at parturition.…”

The role of lactogenic hormones in maternal behavior in female rats

“…These findings establish that during pregnancy, rPL-11, and possibly rPL-I, which is secreted between days 10 and 13 of gestation, gain access to the CSF. Additional support for the concept that rPLs are transported into the CSF from blood during gestation is the recent finding that rPL-I binds to the choroid plexus in female rats (58). Interestingly, in women, human chorionic gonadotrophin (hCG) and human placental lactogen (hPL) are detectable in CSF during pregnancy (59).…”