Search for: All records

Abstract In euryhaline fish, prolactin (Prl) plays an essential role in freshwater (FW) acclimation. In the euryhaline and eurythermal Mozambique tilapia,Oreochromis mossambicus,Prl cells are model osmoreceptors, recently described to be thermosensitive. To investigate the effects of temperature on osmoreception, we incubated Prl cells of tilapia acclimated to either FW or seawater (SW) in different combinations of temperatures (20, 26 and 32 °C) and osmolalities (280, 330 and 420 mOsm/kg) for 6 h. Release of both Prl isoforms, Prl₁₈₈and Prl₁₇₇, increased in hyposmotic media and were further augmented with a rise in temperature. Hyposmotically-induced release of Prl₁₈₈, but not Prl₁₇₇, was suppressed at 20 °C. In SW fish, mRNA expression ofprl₁₈₈increased with rising temperatures at lower osmolalities, while andprl₁₇₇decreased at 32 °C and higher osmolalities. In Prl cells of SW-acclimated tilapia incubated in hyperosmotic media, the expressions of Prl receptors,prlr1 and prlr2,and the stretch-activated Ca²⁺channel,trpv4,decreased at 32 °C, suggesting the presence of a cellular mechanism to compensate for elevated Prl release. Transcription factors,pou1f1,pou2f1b,creb3l1,cebpb,stat3,stat1aandnfat1c, known to regulateprl₁₈₈andprl₁₇₇,were also downregulated at 32 °C. Our findings provide evidence that osmoreception is modulated by temperature, and that both thermal and osmotic responses vary with acclimation salinity. 

Prolactin (PRL) cells within the rostral pars distalis (RPD) of euryhaline and eurythermal Mozambique tilapia, Oreochromis mossambicus, rapidly respond to a hyposmotic stimulus by releasing two distinct PRL isoforms, PRL 188 and PRL 177 . Here, we describe how environmentally relevant temperature changes affected mRNA levels of prl 188 and prl 177 and the release of immunoreactive prolactins from RPDs and dispersed PRL cells. When applied under isosmotic conditions (330 mosmol/kgH 2 O), a 6°C rise in temperature stimulated the release of PRL 188 and PRL 177 from both RPDs and dispersed PRL cells under perifusion. When exposed to this same change in temperature, ∼50% of dispersed PRL cells gradually increased in volume by ∼8%, a response partially inhibited by the water channel blocker, mercuric chloride. Following their response to increased temperature, PRL cells remained responsive to a hyposmotic stimulus (280 mosmol/kgH 2 O). The mRNA expression of transient potential vanilloid 4, a Ca 2+ -channel involved in hyposmotically induced PRL release, was elevated in response to a rise in temperature in dispersed PRL cells and RPDs at 6 and 24 h, respectively; prl 188 and prl 177 mRNAs were unaffected. Our findings indicate that thermosensitive PRL release is mediated, at least partially, through a cell-volume-dependent pathway similar to how osmoreceptive PRL release is achieved.