The Octadecaneuropeptide Stimulates Somatolactin Release from Cultured Goldfish Pituitary Cells

Abstract

The present study aimed to investigate the distribution of the octadecaneuropeptide (ODN) in the goldfish brain and to look for a possible effect of ODN on somatolactin (SL) release from pituitary cells. A discrete population of ODN‐immunoreactive neurones was localised in the lateral part of the nucleus lateralis tuberis. These neurones sent projections through the neurohypophyseal tract towards the neurohypophysis, and nerve fibres were seen in the close vicinity of SL‐producing cells in the pars intermedia. Incubation of cultured goldfish pituitary cells with graded concentrations of ODN (10−9–10−5 m) induced a dose‐dependent stimulation of SL‐β, but not SL‐α, release. ODN‐evoked SL release was blocked by the metabotrophic endozepine receptor antagonist cyclo1–8[DLeu5]OP but was not affected by the central‐type benzodiazepine receptor antagonist flumazenil. ODN‐induced SL release was suppressed by treatment with the phospholipase C (PLC) inhibitor U‐73122 but not with the protein kinase A (PKA) inhibitor H‐89. These results indicate that, in fish, ODN produced by hypothalamic neurones acts as a hypophysiotrophic neuropeptide stimulating SL release. The effect of ODN is mediated through a metabotrophic endozepine receptor positively coupled to the PLC/inositol 1,4,5‐trisphosphate/protein kinase C‐signalling pathway.

Novel Functional Role of NK3R Expression in the Potentiating Effects on Somatolactin α Autoregulation in grass carp pituitary cells

“…To date, SL has been shown to be involved in diverse functions in fish models, including chromatophore proliferation and differentiation6, pigment aggregation7, inflation of swim bladder during embryo development5, reproduction3, stress responses8, lipid metabolism9, and osmoregulation10. At the pituitary level, somatolactin secretion and gene expression are known to be under the control by various hypothalamic factors, e.g., dopamine11, GnRH1213, PACAP4, neurokinin B (NKB)14, MCH15 and octadecdaneuropeptide16. Recently, insulin-like growth factors (IGFs) have also been identified as potent stimulators for SLα and SLβ secretion and gene expression in grass carp pituitary cells17.…”