Meeting Abstract

92.10  Wednesday, Jan. 7  Seasonal and developmental expression of growth hormone regulatory neuropeptides in Atlantic salmon (Salmo salar). BAKER, D.M.*; MCCORMICK, S.D.; Univ. of Mary Washington; USGS, Conte Anadromous Fish Research Center dbaker2@umw.edu

In Atlantic salmon, Salmo salar, circulating levels of growth hormone (GH) are known to vary with developmental stage and season. GH levels increase dramatically in spring in fish transforming from freshwater-adapted parr to seawater-adapted smolts. The vernal increase in GH is entrained by photoperiod: early exposure to a long-day photoperiod advances the increase in GH. We investigated the role of the neurohormones pituitary adenylate cyclase-activating polypeptide (PACAP, a GH secretagogue) and somatostatin I and II (inhibitors of GH secretion) in mediating these changes in GH levels by measuring the respective mRNA transcript levels throughout the spring. In one study, brains were collected from parr and presumptive smolts throughout the spring months. In a second study, brains were collected from fish exposed to an advanced photoperiod in early spring. For both studies, RNA was extracted separately from the hypothalamus and telencephalon, and mRNA transcripts were measured by quantitative PCR. Hypothalamic somatostatin mRNA levels declined from March to May in both parr and smolts. Hypothalamic somatostatin mRNA levels also declined in fish exposed to an advanced long-day photoperiod, compared to natural photoperiod controls. No significant differences in levels of PACAP mRNA were detected in the hypothalamus. Analysis of the mRNA levels of these neuropeptides in the telencephalon is in progress and will also be presented.