Prolactin Expression in the Sheep Brain

Abstract

Accumulating evidence in rodents suggests that a prolactin locally synthesized and released within the brain can act together with that taken up from the circulation to modulate neuroendocrine responses. The present study was designed to identify the regional patterns of prolactin expression in the adult and developing sheep brain. Specifically, we tested the hypothesis that prolactin is expressed in regions of the adult and fetal sheep brain that are critical in the development of neuroendocrine homeostatic and behavioral functions. The expression of prolactin protein in sheep brain was demonstrated by Western blot analysis and brain prolactin mRNA was detected and sequenced using RT-PCR. In situ hybridization histochemistry revealed that prolactin mRNA was expressed in the medial preoptic area, periventricular preoptic nucleus, bed nucleus of the stria terminalis, and in the paraventricular nucleus of the hypothalamus, particularly the ventral region. The neuroanatomical distribution of prolactin mRNA was best visualized in the fetus and prolactin-immunoreactive neurons could also be identified in late gestation fetuses. Brain prolactin mRNA was expressed as early as day 60 of gestation and increased as the fetus aged and peaked at day 135 (term = 147 days). Prolactin mRNA expression did not exhibit a sex difference in the preoptic area, but in the amygdala prolactin mRNA was significantly higher in females than in males at day 100 of gestation. We conclude that prolactin expressed in adult and fetal sheep brain could be involved in neurodevelopment and/or modulation of the neuroendocrine stress axis, although it is too early to rule out other possibilities given the diverse actions that have been attributed to prolactin.

Tissue-specific regulation of porcine prolactin receptor expression by estrogen, progesterone, and prolactin

“…PRL regulates its own secretion at the level of the hypothalamus, where the wide influence of PRL on brain functions is thought to be required for neurobiological adaptations during preparation for pregnancy and lactation . The detection of pPRL mRNA expression in the brain and hypothalamus was expected given data from rats , sheep (Roselli et al 2008), and mice (Chen et al 2004). Combined, these data suggest that PRL may mediate some actions in the brain by acting as a neuropeptide as well as a neuroendocrine hormone .…”

“…Extrapituitary sources of PRL in humans, rodents, and ruminants include uterine and brain tissues, lacrimal, sweat, and adrenal glands, immune and mammary epithelial cells, skin fibroblasts, kidney, and the ovary (Fields et al 1993, Doppler 1994, Ben-Jonathan et al 1996, Prigent-Tessier et al 1999, Sakai et al 1999, Tao et al 2004, Kobayashi et al 2007, Roselli et al 2008. Interestingly, PRL appears to not be expressed in the rat liver (Kurtz et al 1993), a tissue rich in PRLR (Bole-Feysot et al 1998).…”

30 years after: CNS actions of prolactin: Sources, mechanisms and physiological significance

“…The original observation of IR-PRL in the hypothalamus of rats 33 was supported by several groups, [34][35][36][37][38][39] although one study showed cross-reactivity of PRL antiserum with pro-opiomelanocortin, 40 which might account for some of the observations. Subsequently, PRL mRNA has been detected in brain tissue by reverse transcriptase-polymerase chain reaction (RT-PCR) [41][42][43][44][45] but, apart from one study identifying expression in fetal sheep brains, 46 it has not been localised by in situ hybridisation. 41,42 One explanation might be that these studies actually detected pituitary PRL after transport from the periphery, although, at least in one of these studies, 36 PRL-like immunoreactivity was not eliminated by hypophysectomy, suggesting that it was unlikely to be of pituitary origin.…”

The Possible Involvement of Salsolinol and Hypothalamic Prolactin in the Central Regulatory Processes in Ewes During Lactation

“…2002), suggesting an activated state of the brain prolactin system during the peripartum period. Recently, Roselli et al. (2008) have shown that in sheep, prolactin is synthesized within the hypothalamus‐preoptic area and amygdala, where they documented the presence of both prolactin protein and mRNA expression.…”