Diminished feeding responsiveness to orexin A (hypocretin 1) in aged rats is accompanied by decreased neuronal activation.
Orexin A is produced in caudal lateral, posterior, perifornical, and dorsomedial hypothalamic areas. Orexin A in the rostro-dorsal lateral hypothalamic area (rLHa) stimulates feeding and activates several feeding-regulatory brain areas. We hypothesized that aging diminishes feeding and c-Fos-immunoreactivity (c-Fos-ir; marker of neuronal activation) response to orexin A. Young (3 mo), middle-aged (12 mo), and old (24 mo) male Fischer 344 rLHa-cannulated rats were injected with orexin A (0.5, 1, and 2 nmol). Food intake was measured at 1, 2, and 4 h. c-Fos-ir in hypothalamic, limbic, and hindbrain regions was measured in two additional sets of rLHa-orexin A injected rats. In a separate study, orexin A effects on feeding and c-Fos-ir were measured in 6-mo-old rats. Orexin A significantly elevated feeding in rats aged 3, 6, and 12 mo in the 0-1 and 1-2- h time intervals, whereas in old rats this was significant in the 1-2 h time interval only. At 1 h, 6-8 (of 14) brain areas showed elevated c-Fos-ir in response to orexin A in 3- and 6-mo-old rats, but 24-mo-old rats exhibited attenuated or absent c-Fos-ir response in all brain regions except the hypothalamic paraventricular nucleus (PVN) and rostral nucleus of the solitary tract (rNTS). Orexin A did not elevate c-Fos-ir in 3-mo-old rats at 2 h after injection, whereas the PVN and mediodorsal thalamic nucleus (MD) showed elevated c-Fos-ir at 2 h in 24-mo-old rats. These data suggest that delayed and diminished feeding responses in old animals may be due to ineffective neural signaling and implicate the orexin A network as one feeding system affected by aging.
Kotz
Catherine M
CM
Veterans Affairs Medical Center, GRECC (11G), One Veterans Drive, Minneapolis, MN 55417, USA. kotzx004@umn.edu
Mullett
Mary A
MA
Wang
ChuanFeng
C
D000375:Aging / Q000502:physiology*; D000818:Animals; D001921:Brain / Q000166:cytology / Q000378:metabolism*; D004435:Eating / Q000187:drug effects* / Q000502:physiology*; D007150:Immunohistochemistry; D047908:Intracellular Signaling Peptides and Proteins / Q000494:pharmacology*; D008297:Male; D020645:Mediodorsal Thalamic Nucleus / Q000378:metabolism; D009474:Neurons / Q000378:metabolism; D009479:Neuropeptides / Q000494:pharmacology*; D000068797:Orexins; D010286:Paraventricular Hypothalamic Nucleus / Q000378:metabolism; D016760:Proto-Oncogene Proteins c-fos / Q000378:metabolism*; D051381:Rats; D011916:Rats, Inbred F344; D013997:Time Factors
D047908:Intracellular Signaling Peptides and Proteins; D009479:Neuropeptides; D000068797:Orexins; D016760:Proto-Oncogene Proteins c-fos