Meeting Abstract
11.2 Jan. 4 Effect of Fasting on Ghrelin Receptors and NPY Expression in the Brain of Tilapia, Oreochromis mossambicus. RILEY, JR., Larry/G.*; FOX, B./Kai; KAIYA, Hiroyuki; DAVIS, Lori/K.; DOROUGH, Casey/P.; HIRANO, Tetsuya; GRAU, E./Gordon; Calif. State Univ., Fresno; Univ. of Hawaii; National Cardiovascular Center Research Institute; Univ. of Hawaii; Calif. State Univ., Fresno; Univ. of Hawaii; Univ. of Hawaii lriley@csufresno.edu
Evidence to date indicates that ghrelin is an important endocrine peptide that links the gastrointestinal system and brain in the regulation of food intake and energy expenditure. In human and rat, plasma levels as well as stomach expression of ghrelin are elevated in fasted animals, suggesting that ghrelin is a driving force behind the elevated plasma levels of GH during fasting. Ghrelin�s orexigenic actions are mediated by the GHS-Rs (1a and 1b) which are localized on NPY neurons. NPY is the most potent appetite stimulant identified thus far. It is suggested that GHS-R1a is the bioactive ghrelin receptor. We have identified tissue distribution of both GHS-R1a and GHS-R1b in tilapia. Studies were undertaken to investigate the effect of fasting on the GH/IGF-I axis, ghrelin, as well as on GHS-R1a, GHS-R1b and NPY expression in the tilapia brain. Brain expression of GHS-R1a was significantly reduced after 1-6 days of fasting. By contrast, GHS-R1b expression was unaffected by fasting. NPY expression was significantly elevated on the second day of fasting but was significantly reduced by day 6 of fasting. One to three days of fasting significantly reduced plasma levels of IGF-I. Conversely, plasma GH levels were unaltered until day 4 of fasting, when a significant elevation was observed. These results illustrate that fasting differentially regulates the expression of GHS-R1a and GHS-R1b in the brain. The observed different temporal response of NPY mRNA to fasting suggests that acute fasting may instruct the animal to search for food, whereas chronic fasting inhibits the feeding center.
