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Am J Physiol Regul Integr Comp Physiol (November 7, 2007). doi:10.1152/ajpregu.00611.2006
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Submitted on August 27, 2006
Accepted on October 17, 2007

Effects of Hindbrain Melanin-Concentrating Hormone and Neuropeptide Y Administration on Licking for Water, Saccharin, and Sucrose Solutions.

John-Paul Baird1*, Catalina Rios1, Jasmine L Loveland1, Janine Beck1, Alice Tran1, and Carrie E. Mahoney1

1 Psychology, Amherst College, Amherst, Massachusetts, United States

* To whom correspondence should be addressed. E-mail: jpbaird{at}amherst.edu.

Melanin-concentrating hormone (MCH) and neuropeptide-Y (NPY) are orexigenic peptides found in hypothalamic neurons that project throughout the forebrain and hindbrain. The effects of fourth ventricle (4V) infusions of NPY (µug) and MCH (5µg) on licking for water, 4mM saccharin, and sucrose (0.1M and 1.0M) solutions were compared to identify the contributions of each peptide to hindbrain-stimulated feeding. NPY increased mean meal size only for the sucrose solutions, suggesting that caloric feedback or taste quality is pertinent to the orexigenic effect; MCH infusions under identical testing conditions failed to produce increases for any tastant. A second experiment also observed no intake effects after MCH doses up to 15µg, supporting the conclusion that MCH-induced orexigenic responses require forebrain stimulation. A third experiment compared the 4V NPY results with those obtained after NPY infusions (5µg) into the third ventricle (3V). In contrast to the effects observed after the 3V NPY injections and previously reported forebrain ICV NPY infusion studies, 4V NPY failed to increase meal frequency for any taste solution, or ingestion rate in early phases of the sucrose meals. Overall, 4V NPY responses were limited to intrameal behavioral processes, whereas forebrain ICV NPY stimulation elicited both consummatory and appetitive responses. The dissociation between MCH and NPY effects observed for 4V injections is consistent with reports that forebrain ICV injections of MCH and NPY produced nearly dichotomous effects on the pattern of licking microstructure, and collectively, the results indicate that the two peptides have separate sites of feeding action in the brain.







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