Effects of hindbrain melanin-concentrating hormone and neuropeptide Y administration on licking for water, saccharin, and sucrose solutions

Abstract

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 (5 microg) and MCH (5 microg) on licking for water, 4 mM saccharin, and sucrose (0.1 and 1.0 M) 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 or licking effects after MCH doses up to 15 microg, 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 (5 microg) into the third ventricle (3V). In contrast to the effects observed after the 3V NPY injections and previously reported forebrain intracerebroventricular (ICV) NPY infusion studies, 4V NPY failed to increase meal frequency for any taste solution or ingestion rate in the 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.

Levels of Cocaine- and Amphetamine-Regulated Transcript in Vagal Afferents in the Mouse Are Unaltered in Response to Metabolic Challenges

“…More importantly, prepro-MCH mRNA was completely undetectable in the mouse nodose ganglion, even in the fasted condition. The absence of MCH in vagal afferents is consistent with the fact that the administration of MCH in the fourth ventricle does not influence food intake (Zheng et al, 2005; Baird et al, 2008). Even though differences in age, strain, bleeds of antibody, and diets may have influenced our results, we are confident that MCH is not produced by the vagal afferents.…”

Decreased Intake of Sucrose Solutions in Orexin Knockout Mice

“…Baird et al (2009) suggested that ICV injection of orexin-A did not affect orosensory evaluation for sucrose solution in rats because the early ingestion rate or lick burst size increased as sucrose concentration was increased from water to 100 mM and 1 M sucrose; however, administration of orexin-A did not alter those measures. The authors also reported that ICV injection of neuropeptide Y increased sucrose solution intake without affecting taste evaluation (Baird et al 2008). Conversely, melanin-concentrating hormone enhanced taste evaluation (Baird et al 2006), and orexin is likely to modulate the sensitivity of peripheral olfactory processing (Apelbaum et al 2005;Hardy et al 2005) and increase olfactory sensitivity (Julliard et al 2007).…”

An analysis of licking microstructure in three strains of mice

“…Furthermore, the identification of neuropeptides that regulate orexigenic and anorexigenic components of feeding provides an opportunity to examine the molecular basis of food intake. Several studies suggest a distinct role for neuropeptides in licking microstructure and ingestive behavior (Aja, Schwartz, Kuhar, & Moran, 2001; Baird et al, 2006, 2008; Zukerman et al, 2009). Combined with the use of mouse genetics and pharmacological studies, microstructural analyses will surely be useful for elucidating the etiology of food intake and associated disorders.…”