Reproductive Experience Increases Prolactin Responsiveness in the Medial Preoptic Area and Arcuate Nucleus of Female Rats

Abstract

The experience of pregnancy plus lactation produces long-term enhancements in maternal behavior as well as reduced secretion of prolactin, a key hormone for the initial establishment of maternal care. Given that prolactin acts centrally to induce maternal care as well as regulate its own secretion, we tested whether prolactin receptors in brain regions known to regulate behavioral and neuroendocrine processes were up-regulated and more responsive to prolactin in reproductively experienced females. Diestrous primiparous (8 wk after weaning) and age-matched virgin rats were treated with 250 microg ovine prolactin sc or vehicle and the brains collected 2 h later for measurement of mRNA for genes involved in prolactin signaling. Reproductively experienced rats had lower serum prolactin concentrations, compared with virgin rats, suggesting enhanced prolactin feedback on the arcuate neurons regulating prolactin secretion. In the medial preoptic area and arcuate nucleus (regions involved in regulating maternal behavior and prolactin secretion, respectively), the level of long-form prolactin receptor mRNA was higher in primiparous rats, and prolactin treatment induced a further increase in receptor expression in these animals. In the same regions, suppressors of cytokine signaling-1 and -3 mRNA levels were also markedly increased after prolactin treatment in reproductively experienced but not virgin rats. These results support the idea that reproductive experience increases central prolactin responsiveness. The induction of prolactin receptors and enhanced prolactin responsiveness as a result of pregnancy and lactation may help account for the retention of maternal behavior and shifts in prolactin secretion in reproductively experienced females.

Reproductive Experience Alters Prolactin Receptor Expression in Mammary and Hepatic Tissues in Female Rats1

“…Thus, prior reproductive experience appears to affect basal levels of casein beta gene expression. This reproductive experience effect is similar to that reported in neural tissue for PrlrL, that is, nonlactating, cycling rats that have previously raised a litter were found to have higher levels of Prlr expression in both the medial preoptic area and the arcuate region compared to levels present in age-matched virgin rats [10]. Further work is needed to assess the effects of reproductive experience on casein beta protein content because measurement of mRNA expression provides only one perspective of the effects of reproductive experience on casein beta's biological activity.…”

“…That multiple pregnancies resulted in a higher level of PrlrL mRNA expression in hepatic tissue parallels the effects of a prior parity on the expression of PrlrL in brain [10]. A similar increase in PrlrS expression was found in hepatic tissues.…”

“…However, it may involve an actual increase in responsiveness to PRL at the receptor level. In agreement with this concept are the findings that a long-term increase in the expression of the long form of the prolactin receptor (PRLRL) as well as its responsiveness to exogenous PRL treatment occur in the brain of experienced female rats after normal estrous cyclicity resumes [10]. Likewise, more recent research has found that basal as well as PRL-stimulated phosphorylated STAT5 activities in the brain are enhanced in reproductively experienced female rats [11].…”

Distribution of prolactin‐responsive neurons in the mouse forebrain

“…The MPN is likely to mediate one of prolactin's most well-documented central nervous system actions: the stimulation of maternal behavior Bridges et al, 2001). In the MPN, enhanced maternal behavior corresponded with an increase in prolactin receptor mRNA expression (Anderson et al, 2006). The PVN has a known role in food intake, with prolactin administration into this nucleus inducing an increase in food intake in rats (Sauve and Woodside, 2000).…”

Characteristic Neurobiological Patterns Differentiate Paternal Responsiveness in Two <i>Peromyscus</i> Species

“…Past research investigating the maternal brain has identified several influential brain areas including the medial preoptic area (MPOA), bed nucleus of the stria terminalis (BNST), medial amygdala (MeA), anterior hypothalamus, nucleus accumbens, hippocampus, and periaqueductal gray [Numan, 1974[Numan, , 2007Kinsley et al, 2006;Numan and Stolzenberg, 2008]. These brain areas are modulated by altered patterns of estrogen, progesterone, prolactin, and oxytocin (OT) release [Bridges et al, 1990;Carter, 1998;Numan and Insel, 2003;Anderson et al, 2006;Bridges and Byrnes, 2006;Tom and Assinder, 2010].…”