Changes in brain mRNA levels of gonadotropin-releasing hormone, pituitary adenylate cyclase activating polypeptide, and somatostatin during ovulatory luteinizing hormone and growth hormone surges in goldfish

Abstract

Canosa LF, Stacey N, Peter RE. Changes in brain mRNA levels of gonadotropin-releasing hormone, pituitary adenylate cyclase activating polypeptide, and somatostatin during ovulatory luteinizing hormone and growth hormone surges in goldfish. Am J Physiol Regul Integr Comp Physiol 295: R1815-R1821, 2008. First published September 24, 2008 doi:10.1152/ajpregu.00166.2008.-In goldfish, circulating LH and growth hormone (GH) levels surge at the time of ovulation. In the present study, changes in gene expression of salmon gonadotropin-releasing hormone (sGnRH), chicken GnRH-II (cGnRH-II), somatostatin (SS) and pituitary adenylate cyclase activating polypeptide (PACAP) were analyzed during temperature-and spawning substrate-induced ovulation in goldfish. The results demonstrated that increases in PACAP gene expression during ovulation are best correlated with the GH secretion profile. These results suggest that PACAP, instead of GnRH, is involved in the control of GH secretion during ovulation. Increases of two of the SS transcripts during ovulation are interpreted as the activation of a negative feedback mechanism triggered by high GH levels. The results showed a differential regulation of sGnRH and cGnRH-II gene expression during ovulation, suggesting that sGnRH controls LH secretion, whereas cGnRH-II correlates best with spawning behavior. This conclusion is further supported by the finding that nonovulated fish induced to perform spawning behavior by prostaglandin F 2␣ treatment increased cGnRH-II expression in both forebrain and midbrain, but decreased sGnRH expression in the forebrain. teleost; neuroendocrine control; spawning behavior; gene expression SPONTANEOUS OVULATION IN MANY teleost species is preceded by a surge of LH release from the pituitary gland that initiates the final maturation of oocytes and the rupture of the ovarian follicle (for a review, see Refs. 38,58,64). In fish, gonadotropin-releasing hormone (GnRH) positively regulates LH synthesis and release.

Immunohistochemical study of pituitary cells in wild and captive Salminus hilarii (Characiformes: Characidae) females during the annual reproductive cycle

“…Additionally, such increases in GH cell activity in the vitellogenic stage could be related to increased feeding during this period, as was observed in other teleost fish (Holloway and Leatherland 1998). It is also probable that in this species, GH secretion is regulated by melatonin, as observed in rainbow trout ( Oncorhynchus mykiss ), and/or by GnRH as suggested by Canosa et al (2008), who demonstrated that the circulating levels of LH and GH increase at the time of ovulation in goldfish.…”

Neuroendocrine regulation of somatic growth in fishes

“…However, the influence of circulating SST on the control of GH secretion has not been clearly addressed in fish. The regulation of GH by SST may be influenced by developmental stage, feeding, and nutritional state [84,85]. Other research suggests that SSTs are involved in the regulation of growth hormone sensitivity of fish hepatocytes, and can cause a reduction in the levels of GHR expression and IGF-1 biosynthesis and secretion [86,87].…”

Central Pathways Integrating Metabolism and Reproduction in Teleosts

“…In the goldfish, GnRH2 stimulates reproductive behavior (188). Furthermore, there is a strong positive correlation between spawning behavior and GnRH2 gene expression (189), suggesting stimulatory role of GnRH2 in reproductive behavior. GnRH2 is also detected in the goldfish pituitary (190) and induces LH release in vitro (120).…”