Galanin, a central appetite factor, affects appetite signals in the hypothalamus and promotes feeding in Siberian sturgeon (Acipenser baerii Brandt)

Abstract

Galanin is a strong appetite promoting factor in mammals, but information about the mechanism of galanin in feeding regulation is very limited in fish. This study investigated the effects of galanin on food intake and explored the feeding regulation mechanism in Siberian sturgeon. Galanin and galanin receptor-3 (galr3) cDNA sequences of 557 bp and 710 bp were obtained respectively, and they were both abundantly expressed in the hypothalamus. Four experiments were performed to determine whether galanin affects food intake in Siberian sturgeon, including short-term fasting, intraperitoneal (i.p.) injection, and intraventricular (i.c.v.) injection. The results showed that galanin mRNA expression increased significantly after fasting for 1 (P < 0.05) and 3 h (P < 0.01). The galanin (0.50, 1.00, and 1.50 μg/g BW) i.p. injection did not significantly change food intake within 1, 3, or 6 h, but the galanin i.c.v. injection concentrations of 0.01, 0.05, and 0.10 μg/g BW significantly increased food intake within 3 h (P < 0.01, P < 0.05, P < 0.001, respectively). An i.c.v. co-injection experiment with galanin and spexin was carried out to further explore the mechanism of galanin on the feeding regulation and to clarify the relationship between galanin and spexin. The results showed that 0.20 μg/g BW spexin significantly reversed the appetite promoting effect of 0.10 μg/g BW galanin (P < 0.05). Moreover, galanin did not affect the expression of galr3, while spexin significantly decreased the transcriptional level of galr3 (P < 0.05). The expression of nine appetite factors (cart, ucn3, apelin, nucb2, npy, cck, galanin, spexin, and pyy), significantly changed among the four groups (saline, galanin, spexin, and galanin + spexin). These results indicate that central galanin promotes food intake, which may have been mediated by the detected down-regulating anorexic signals including cart, ucn3, and pyy in the hypothalamus. Spexin reduced appetite, probably related to the upregulation of cart and ucn3 transcript expression and down-regulation of npy. This investigation provides a theoretical basis for an in-depth analysis of the feeding regulation mechanism in teleost.