Submitted on March 4, 2008
Accepted on September 22, 2008
Changes in brain mRNA levels of GnRH, PACAP and SS during ovulatory LH and GH surges in goldfish
Luis Fabian Canosa1*, Norm Stacey2, and Richard Ector Peter3
1 CW-405 Dept. of Biological Sciences, University of Alberta, Edmonton,, T6G 2E9, Canada; IIB-INTECH-UNSAM, Chascomus, Buenoa Aires, Argentina
2 CW-405 Dept. of Biological Sciences, University of Alberta, Edmonton, Canada
3 CW-405 Dept. of Biological Sciences, University of Alberta, Edmonton,, T6G 2E9, Canada; Bamfield Marine Sciences Centre, Bamfield, Canada
* To whom correspondence should be addressed. E-mail: lcanosa{at}intech.gov.ar.
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 GnRH (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 GHRH/PACAP gene expression during ovulation are best correlated with the GH secretion profile. These results suggest that GHRH/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 non-ovulated fish induced to perform spawning behavior by prostaglandin F2
treatment increased cGnRH-II expression in both forebrain and midbrain, but decreased sGnRH expression in the forebrain.
