title: Short-term regulation of the hypothalamic melanocortinergic system under fasting and defined glucose-refeeding conditions in rats: a laser capture microdissection (LMD)-based study.
abstract: It is well established that under fasting conditions the expression of the orexigenic neuropeptide agouti-related peptide (AGRP) is up-regulated in the hypothalamic arcuate nucleus (ARC), while inconsistent data exist regarding fasting regulation of the anorexigenic neurohormone proopiomelanocortin (POMC). Inconsistencies might have methodological reasons, especially concerning neuromorphological and/or experimental (nutritional) specificity. We analyzed the expression of both neuropeptides in ARC neurons, using lasercapture microdissection (LMD) and real-time PCR in 12h fasted vs. fed Wistar rats as well as after a standardized glucose load, i.e., under clinically relevant conditions in terms of diagnosing glucose intolerance in the human. Under fasting conditions, clear up-regulation of AGRP was observed, with increasing magnitude in ARC single neurons (SNP) as compared to ARC cell layers (+125% vs. +23%, resp.), closely correlated to hypoinsulinemia and hypoleptinemia. Surprisingly, in the fasting state POMC was not found to be down-regulated, neither in ARC cell layers nor in ARC single neurons (+9% vs. +6%). However, glucose-refeeding under diagnostically relevant conditions led to strong neuronal up-regulation of POMC expression in ARC SNP (+128%), and AGRP down-regulation (-50%). In conclusion, experimentally, topographically, and analytically specific and standardized conditions confirmed AGRP in ARC neurons as being neuronally up- and down-regulated, resp., depending on the general nutritional state, while POMC was found to be (up-) regulated only after peripheral glucose load. Findings suggest that POMC in ARC neurons acts glucose-mediated as an "anti-orexigenic" neurohormone, specifically responding to hyperglycemia.
authors.affiliation: Clinic of Obstetrics, Research Group Experimental Obstetrics, Charité - Universitätsmedizin Berlin, Berlin, Germany.
authors.forename: Emelie M
authors.initials: EM
authors.lastname: Landmann
authors.forename: Karen
authors.initials: K
authors.lastname: Schellong
authors.forename: Kerstin
authors.initials: K
authors.lastname: Melchior
authors.forename: Elke
authors.initials: E
authors.lastname: Rodekamp
authors.forename: Thomas
authors.initials: T
authors.lastname: Ziska
authors.forename: Thomas
authors.initials: T
authors.lastname: Harder
authors.forename: Andreas
authors.initials: A
authors.lastname: Plagemann
mesh_terms: D054369:Agouti-Related Protein / Q000096:biosynthesis*; D000818:Animals; D004435:Eating / Q000502:physiology; D005215:Fasting / Q000378:metabolism*; D005947:Glucose / Q000378:metabolism*; D007031:Hypothalamus / Q000378:metabolism*; D061346:Laser Capture Microdissection / Q000379:methods*; D008297:Male; D011333:Pro-Opiomelanocortin / Q000096:biosynthesis*; D051381:Rats; D017208:Rats, Wistar; D013997:Time Factors
chemical_list: C515197:AGRP protein, rat; D054369:Agouti-Related Protein; D011333:Pro-Opiomelanocortin; D005947:Glucose