Neuropeptide control of growth hormone surge during ovulation in goldfish

CANOSA LF; PETER RE

JOURNAL OF EXPERIMENTAL ZOOLOGY

WILEY-LISS, DIV JOHN WILEY & SONS INC

Año: 2006 vol. 305A p. 115 - 115

0022-104X

In the present study changes in gene expression of somatostatin (SS) and growth hormone-releasing hormone /pituitary adenylate cyclase activating polypeptide (GHRH/PACAP) during spontaneous ovulation in goldfish were analyze. In goldfish, it was found that, circulating growth hormone (GH) and gonadotropin (GTH) levels peak previous to ovulation. Concomitantly, it was demonstrated a decrease in gonadotroping-releasing hormone (GnRH) content in telencephalon and hypothalamus; interpreted as a sign of GnRH release. Considering that GnRH stimulates both GTH and GH secretion, it was concluded that the activation of GnRH neuronal system might be a common pathway in the stimulation of both GTH and GH during spawning. The control of pituitary GH secretion in fish is multifactorial, with a balance of stimulatory and inhibitory factors. SS is the major inhibitors, while a number of peptides stimulate GH release such as GHRH, PACAP, and GnRH among others. In this study, mature female goldfish were acclimatized to a 16:8L-D cycle and 12 C. The spontaneous ovulation was induced by increasing the water temperature to 20 C, introduction of artificial vegetation and mature males in the tanks (experimental conditions). Control conditions represent females that remained at 12 C without vegetation or male. Our results confirm previously data showing increased circulation levels of GTH and GH during spawning. Besides, we found that gene expression of GHRH/PACAP, PSS-I and PSS-III significantly increases with ovulation. No significant changes in PSS-II gene expression were found. These results suggest that, in addition to GnRH, GHRH/PACAP could also be involved in the control of GH secretion during ovulation. Increments in two of the SS transcripts are interpreted as the activation of a negative feedback mechanism triggered by high GH levels.