Effect of Suckling on Prolactin Receptor Immunoreactivity in the Hypothalamus of the Rat

Pi, Xiujun; Voogt, James L.

doi:10.1159/000054551

Cited by 28 publications

(20 citation statements)

References 34 publications

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“…Hence, it is tempting to speculate that the reduction in mRNA for the long-form PRL-R within the arcuate nucleus during lactation might contribute to the loss of responsiveness of TIDA neurones to prolactin. Alternatively, since the PRL-R antibodies used in previous research (Pi & Grattan 1999a, Pi & Voogt 2000 do not distinguish between the two isoforms, it is possible that the observed increase in PRL-R immunoreactivity represents expression of the short form of the receptor. Levels of the short-form PRL-R mRNA remain relatively high in the arcuate nucleus during late pregnancy and lactation.…”

Section: Discussionmentioning

confidence: 97%

Quantitation of prolactin receptor mRNA in the maternal rat brain during pregnancy and lactation

Augustine¹,

Kokay²,

Andrews³

et al. 2003

Journal of Molecular Endocrinology

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Prolactin receptor (PRL-R) expression in the brain is increased in lactating rats compared with non-pregnant animals. The aim of the present study was to determine the time-course of changes in PRL-R mRNA levels during pregnancy and/or lactation, and to determine relative levels of the two forms (short and/or long form) of receptor mRNA in specific brain regions. Brains were collected from female rats on dioestrus, days 7, 14 or 21 of pregnancy, day 7 of lactation or day 7 post-weaning. Frozen, coronal sections were cut (300 µm) and specific hypothalamic nuclei and the choroid plexus were microdissected using a punch technique. Total RNA was extracted and reverse transcribed, then first strand cDNA was amplified using quantitative real-time PCR. Results showed an up-regulation of long-form PRL-R mRNA in the choroid plexus by day 7 of pregnancy compared with dioestrus, which further increased on days 14 and 21 of pregnancy and day 7 of lactation, and then decreased to dioestrous levels on day 7 post-weaning. Short-form PRL-R mRNA levels increased on day 14 of pregnancy relative to dioestrus, increased further on day 7 of lactation and decreased on day 7 post-weaning. Changes in mRNA were reflected in increased levels of PRL-R immunoreactivity in the choroid plexus during pregnancy and lactation, compared with dioestrus. In the arcuate nucleus, long-form PRL-R mRNA was increased during pregnancy. In contrast to earlier work, no significant changes in short-or long-form PRL-R mRNA expression were detected in several other hypothalamic nuclei, suggesting that changes in hypothalamic mRNA levels may not be as marked as previously thought. The up-regulation of PRL-R mRNA and protein expression in the choroid plexus during pregnancy and lactation suggest a possible mechanism whereby increasing levels of peripheral prolactin during pregnancy may have access to the central nervous system. Together with expression of long-form PRL-R mRNA in specific hypothalamic nuclei, these results support a role for prolactin in regulating neuroendocrine and behavioural adaptations in the maternal brain.

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Section: Discussionmentioning

confidence: 97%

Quantitation of prolactin receptor mRNA in the maternal rat brain during pregnancy and lactation

Augustine¹,

Kokay²,

Andrews³

et al. 2003

Journal of Molecular Endocrinology

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“…Interestingly, PRL-R expression in the choroid plexus is markedly increased during pregnancy and lactation (2), suggesting increased access of prolactin to brain structures during these conditions. Similarly, levels of PRL-R protein in the hypothalamus appear to increase during lactation compared with nonpregnant rats (47)(48)(49). These observations suggest that prolactin may be a major regulator of hypothalamic function, particularly during pregnancy and lactation, when prolactin levels are elevated (22,23).…”

mentioning

confidence: 83%

Expression of the long form of the prolactin receptor in magnocellular oxytocin neurons is associated with specific prolactin regulation of oxytocin neurons

Kokay¹,

Bull²,

Davis³

et al. 2006

American Journal of Physiology-Regulatory, Integrative and Comp

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neurons of the supraoptic (SON) and paraventricular nuclei (PVN) show considerable plasticity during pregnancy and lactation. Prolactin receptors (PRL-R) have been identified in both these nuclei. The aim of this study was to investigate the cell type(s) expressing mRNA for the long form of prolactin receptor (PRL-R L) and to determine whether patterns of expression change during pregnancy and lactation. In addition, we examined effects of prolactin on excitability of oxytocin and vasopressin neurons. Sections from brains of nonpregnant, pregnant, and lactating rats were hybridized with an 35 S-labeled probe to label PRL-RL mRNA together with digoxigenin-labeled probes to detect either oxytocin or vasopressin mRNA. In the SON, PRL-R L mRNA was predominantly colocalized with oxytocin mRNA, with over 80% of oxytocin neurons positive for PRL-R L mRNA. Very few (Ͻ10%) vasopressin neurons expressed PRL-R L mRNA. In the PVN, PRL-RL mRNA was also predominantly found in oxytocin neurons, and the proportion of PRL-R L-positive oxytocin neurons increased significantly during pregnancy and lactation. As in the SON, relatively few vasopressin cells contained PRL-R L mRNA. For in vivo electrophysiology, nonpregnant rats were anesthetized, and then extracellular single neuron activity was recorded in identified oxytocin and vasopressin neurons. After a period of baseline recording, the effect of prolactin (1 g icv) on firing rate was examined. Prolactin treatment of nonpregnant rats induced a significant decrease in firing rates of oxytocin neurons. There was no effect of prolactin on the activity of vasopressin neurons. Together, these data provide strong evidence that prolactin directly and specifically regulates activity of oxytocin neurons. pregnancy; lactation; magnocellular neurons; in situ hybridization IN ADDITION TO ITS CRITICAL actions in mammary gland function during pregnancy and lactation, the anterior pituitary hormone prolactin exerts important actions within the brain. Prolactin is thought to gain access to the brain through a carrier-mediated transport system (74), likely involving prolactin receptors in the choroid plexus (51, 64). Prolactin receptor (PRL-R) mRNA (3,4,11,45) and protein (13, 46) have been identified in many hypothalamic nuclei. Interestingly, PRL-R expression in the choroid plexus is markedly increased during pregnancy and lactation (2), suggesting increased access of prolactin to brain structures during these conditions. Similarly, levels of PRL-R protein in the hypothalamus appear to increase during lactation compared with nonpregnant rats (47-49). These observations suggest that prolactin may be a major regulator of hypothalamic function, particularly during pregnancy and lactation, when prolactin levels are elevated (22,23).Within the hypothalamus, the neurons that undergo one of the most dramatic changes during pregnancy and lactation are the magnocellular neurons of the supraoptic (SON) and paraventricular (PVN) nuclei (26). PRL-R mRNA has been identified in both of these nuclei (3, 4...

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“…In nonsuckling rats, which had no hyperprolactinemia and the suckling-induced PRL surge (1,34), most parameters with the exception of trabecular thickness were not much different from those of the age-matched control rats (Figs. 7-9).…”

Section: E430 Osteoregulatory Role Of Prolactin In Lactating Ratsmentioning

confidence: 95%

“…After delivery, litter size was adjusted to eight pups per dam for lactating groups, whereas in nonsuckling groups all pups were permanently separated from dams from birth. Such nonsuckling mothers were reported to have no hyperprolactinemia because the suckling-induced PRL surge was absent, and plasma PRL levels rapidly declined within 12 h after cessation of suckling (26,34). In some experiments, dams were injected daily subcutaneously for 7 days with 4 mg/kg Bromo sc (Sigma, St. Louis, MO) or BromoϩPRL (purified from ovine pituitary gland; catalog no.…”

Section: Methodsmentioning

confidence: 99%

Bone modeling in bromocriptine-treated pregnant and lactating rats: possible osteoregulatory role of prolactin in lactation

Suntornsaratoon

Wongdee

Goswami

et al. 2010

American Journal of Physiology-Endocrinology and Metabolism

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The lactogenic hormone prolactin (PRL) directly regulates osteoblast functions in vitro and modulates bone remodeling in nulliparous rats, but its osteoregulatory roles in pregnant and lactating rats with physiological hyperprolactinemia remained unclear. Herein, bone changes were investigated in rats treated with bromocriptine (Bromo), an inhibitor of pituitary PRL release, or BromoϩPRL at different reproductive phases, from mid-pregnancy to late lactation. PRL receptors were strongly expressed in osteoblasts lining bone trabeculae, indicating bone as a target of PRL actions. By using dual energy X-ray absorptiometry, we found a significant increase in bone mineral density in the femora and vertebrae of pregnant rats. Such pregnancyinduced bone gain was, however, PRL independent and may have resulted from the increased cortical thickness. Bone trabeculae were modestly changed during pregnancy as evaluated by bone histomorphometry. On the other hand, lactating rats, especially in late lactation, showed massive bone loss in bone trabeculae but not in cortical shells. Further study in Bromo-and BromoϩPRL-treated rats suggested that PRL contributed to decreases in trabecular bone volume and number and increases in trabecular separation and eroded surface, as well as a paradoxical increase in bone formation rate in late lactation. Uncoupling of trabecular bone formation and resorption was evident in lactating rats, with the latter being predominant. In conclusion, pregnancy mainly induced cortical bone gain, whereas lactation led to trabecular bone loss in both long bones and vertebrae. Although PRL was not responsible for the pregnancy-induced bone gain, it was an important regulator of bone modeling during lactation. bone histomorphometry; hyperprolactinemia; ion chromatography; osteopenia; uncoupling IN PREGNANT AND BREASTFEEDING WOMEN, massive calcium loss occurs for fetal development (ϳ200 -300 mg/day) and lactogenesis (ϳ300 -1,000 mg/day), respectively (4,23,36). A huge amount of calcium demand is accomplished, in part, by enhanced intestinal calcium absorption during these reproductive periods (9). Our recent studies in rats demonstrated that the lactogenic hormone prolactin (PRL), released from the anterior pituitary gland during pregnancy (ϳ100 -200 ng/ml) and lactation (ϳ200 -300 ng/ml), was the principal calciotropic maternal hormone, which was capable of stimulating calcium absorption in the small intestine and proximal large intestine (7, 21). Moreover, lactation-induced bone resorption provides additional calcium to match the increased calcium demand of the offspring, which in turn induces reversible osteopenia in mothers (20,36).In both humans and rodents, hormonal regulation of bone changes during pregnancy and lactation is not completely understood, but it is not directly regulated by the major calciotropic hormones, namely parathyroid hormone (PTH) and 1,25-dihydroxyvitamin D 3 [1,25(OH) 2 D 3 ] (9, 30, 36). Other hormones with elevated plasma levels, such as PRL, PTHrelated peptide (PTHrP), calcit...

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Effect of Suckling on Prolactin Receptor Immunoreactivity in the Hypothalamus of the Rat

Cited by 28 publications

References 34 publications

Quantitation of prolactin receptor mRNA in the maternal rat brain during pregnancy and lactation

Quantitation of prolactin receptor mRNA in the maternal rat brain during pregnancy and lactation

Expression of the long form of the prolactin receptor in magnocellular oxytocin neurons is associated with specific prolactin regulation of oxytocin neurons

Bone modeling in bromocriptine-treated pregnant and lactating rats: possible osteoregulatory role of prolactin in lactation

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