Expression of prolactin-releasing peptide and prolactin in the euryhaline mudskippers (Periophthalmus modestus): prolactin-releasing peptide as a primary regulator of prolactin

Abstract

Prolactin (PRL)-releasing peptide (PrRP) is a strong candidate stimulator of pituitary PRL transcription and secretion in teleosts. However, the role in control of extrapituitary PRL expression is unclear even in mammals. To study the possible presence of PrRP-PRL axes not only in the brain-pituitary but also in peripheral organs, the expression patterns of PrRP, PRL and growth hormone (GH) were characterized in amphibious euryhaline mudskippers (Periophthalmus modestus). PrRP mRNA is abundantly expressed not only in the brain but also in the liver, gut and ovary, while less abundant expression was also detected in the skin and kidney. Corresponding to the distribution of PrRP mRNA, PRL mRNA was also detectable in these organs. During adaptation to different environments, the changes in mRNA levels of PrRP paralleled those in PRL in the brain-pituitary, liver and gut in an organ-specific manner. Brain PrRP mRNA and the pituitary PRL mRNA increased under freshwater and terrestrial conditions (P,0·05); expression of PrRP and PRL in the gut of freshwater fish was higher (P,0·05) than those in sea-water fish although there were no changes in fish kept out of water; no significant change was seen in the liver. Expressions of GH were not correlated with PrRP. In the gut, PrRP and PRL appear to be co-localized in the mucosal layer, especially in the mucous cells. Thus, PrRP may also be a local modulator of extrapituitary PRL expression and the PrRP-PRL axes in various organs may play an organ-specific role during environmental adaptation.

Prolactin-releasing peptide, food intake, and hydromineral balance in goldfish

“…16). Furthermore, they parallel previous observations that reported higher brain PrRP and pituitary PRL mRNA expression in a euryhaline fish species acclimated to a hyposmotic environment relative to a hyperosmotic environment (24).…”

“…16). With evidence suggesting PrRP to be an important PRL secretagogue in fish (18,23,27), observations that brain PrRP mRNA and pituitary PRL mRNA expression elevate in fish acclimated to freshwater (FW), relative to those acclimated to seawater, are consistent with the generally accepted actions of PRL as a "FW osmoregulatory hormone" and PrRP as a PRF under such conditions (24).…”

“…Much less is known about the potential appetite-regulating effects of PrRP in nonmammalian vertebrates. Recent studies have suggested that PrRP may be involved in both the regulation of feeding and energy metabolism in aves (30,31), and anecdotal reports have introduced a scenario whereby PrRP "induction" in bony fish may result in poor growth (24). However, to the best of our knowledge, there are no published studies that address a potential role for PrRP in the regulation of food intake in fish.…”

Expression of glucocorticoid receptor in the intestine of a euryhaline teleost, the Mozambique tilapia (Oreochromis mossambicus): Effect of seawater exposure and cortisol treatment

“…Immunocytochemical staining was carried out by the avidin -biotin peroxidase complex (ABC) method (Hsu et al, 1981) using Vectastain ABC Kit (Vector Laboratories, Burlingame, CA) basically as described in Uchida et al (1996) and Sakamoto et al (2005). The intestine was fixed overnight in 4% paraformaldehyde in 0.1 M phosphate buffer (pH 7.4) at 4 -C. The posterior part of the intestine was dehydrated in ethanol and embedded in paraplast.…”

Prolactin and the physiological regulation of its secretion. A review

“…Recently much attention is paid to a group of peptides that have been identified in mammals (Hinuma et al, 1998;Iijima et al, 1999;Fuji et al, 1999;Maruyama et al, 1999;Ibata et al, 2000), birds (Tachibana et al, 2011), fishes (Fujimoto et al, 1998;Satake et al, 1999;Moriyama et al, 2002;Seale et al, 2002;Sakamoto et al, 2005), amphibians (Sakamoto et al, 2006) as the prolactin releasing peptides (PrRPs). These animals have several forms of PrRPs with different numbers of amino acids (20,25,31,32,37) and different effects on prolactin release (Tachibana et al, 2011).…”