Changes in Hypothalamic Expression Levels of Galanin-Like Peptide in Rat and Mouse Models Support That It Is a Leptin-Target Peptide

Abstract

Galanin-like peptide (GALP) is a novel peptide that has been isolated from the porcine hypothalamus. The expression of GALP mRNA is localized to the hypothalamic arcuate nucleus and is thought to be under the regulation of leptin. First, we confirmed by real-time PCR analysis that sc administration of leptin to Wistar rats under food-deprived conditions resulted in a 1.5-fold increase in hypothalamic GALP mRNA levels. Next, GALP mRNA levels were found to be reduced by 50% in 11-wk-old male Zucker obese rats compared with age-matched Zucker lean rats, whereas neuropeptide Y mRNA levels were increased by 55% and proopiomelanocortin mRNA levels were reduced by 53% in Zucker obese rats. Analysis using a two-site enzyme immunoassay revealed a lower level of hypothalamic GALP immunoreactivity in 11-wk-old Zucker obese rats (5.9 fmol/mg protein) than in age-matched Zucker lean rats (19.6 fmol/mg protein). Immunohistochemical studies demonstrated that Zucker obese rats (11 wk old) had a reduced number of GALP immunoreactivity-positive cells (29.4 cells/3 slices) in the arcuate nucleus compared with age-matched Zucker lean rats (115 cells/3 slices). Furthermore, Zucker obese rats showed increased sensitivity to intracerebroventricularly administered GALP compared with Zucker lean rats, in that a lower dose of GALP increased plasma LH levels in male Zucker obese rats, but not in male Zucker lean rats. In addition, a reduction in the level of hypothalamic GALP mRNA was found in db/db and ob/ob mice. The result supports the hypothesis that the hypothalamic GALP gene expression is controlled by leptin signals and suggests possible involvement of GALP in the reproductive abnormalities of the Zucker obese rat.

Caloric restriction: Impact upon pituitary function and reproduction

“…GALP is specifically expressed in the arcuate nucleus of the hypothalamus. GALP expression is tightly linked to the metabolic state of the organism as its expression is regulated by both circulating levels of leptin and insulin (Kumano et al, 2003;Fraley et al, 2004). GALPpositive neurons appear to be directly stimulated by leptin as they possess the ObRb leptin receptor.…”

Stimulation of sexual behavior in the male rat by galanin-like peptide

“…GALP shares a partial amino acid sequence identity with galanin and binds to several galanin receptor subtypes; however, GALP is derived from its own unique gene, distinct from galanin (Ohtaki et al, 1999). GALP is expressed in the brain, primarily in the hypothalamic arcuate nucleus (ARC), where it is regulated by various metabolic signals, including leptin, insulin, and metabolic fuels (Fraley et al, 2003a(Fraley et al, , 2004Juréus et al, 2000Juréus et al, , 2001Kumano et al, 2003). Centrally administered GALP has marked effects on feeding and body weight in the rat and mouse (Gundlach, 2002;Krasnow et al, 2003;Lawrence et al, 2002;Matsumoto et al, 2002;Seth et al, 2002Seth et al, , 2003a, and it activates the sympathetic nervous system in the mouse (Hansen et al, 2003).…”

Galanin-like peptide: a key player in the homeostatic regulation of feeding and energy metabolism?

“…45 Leptin administration restores GALP-expressing cells in fasted rats 26 and ob/ob mice. 9 It also induces a significant increase in GALP mRNA levels in the hypothalamus, and GALP mRNA levels are reduced in the hypothalamus of Zucker obese rats and db/db and ob/ob obese mice, 10 with GALP mRNA expression in ob/ob mice being reversed by leptin replacement. 10 These findings clearly show that leptin positively regulates GALPrelated neuronal activity in the hypothalamus.…”

“…9 It also induces a significant increase in GALP mRNA levels in the hypothalamus, and GALP mRNA levels are reduced in the hypothalamus of Zucker obese rats and db/db and ob/ob obese mice, 10 with GALP mRNA expression in ob/ob mice being reversed by leptin replacement. 10 These findings clearly show that leptin positively regulates GALPrelated neuronal activity in the hypothalamus. Fraley et al 23 have also demonstrated that GALP-containing neurons are responsive to changes in circulating concentrations of insulin using streptozotocin-induced diabetic rats and central injection of insulin into the fasted rat.…”