Exogenous prolactin-releasing peptide's orexigenic effect is associated with hypothalamic neuropeptide Y in chicks

Reproductive Regulation of PrRPs in Teleost: The Link Between Feeding and Reproduction

Prolactin-releasing peptide (PrRP), a sort of vital hypothalamic neuropeptide, has been found to exert an enormous function on the food intake of mammals. However, little is known about the functional role of PrRP in teleost. In the present study, two PrRP isoforms and four PrRP receptors were isolated from grass carp. Ligand-receptor selectivity displayed that PrRP1 preferentially binds with PrRP-R1a and PrRP-R1b, while PrRP-R2a and PrRP-R2b were special receptors for PrRP2. Tissue distribution indicated that both PrRPs and PrRP-Rs were highly expressed in the hypothalamus-pituitary-gonad axis and intestine, suggesting a latent function on food intake and reproduction. Using grass carp as a model, we found that food intake could significantly induce hypothalamus PrRP mRNA expression, which suggested that PrRP should be also an anorexigenic peptide in teleost. Interestingly, intraperitoneal (IP) injection of PrRPs could significantly induce serum luteinizing hormone (LH) secretion and pituitary LHβ and GtHα mRNA expression in grass carp. Moreover, using primary culture grass carp pituitary cells as a model, we further found that PrRPs could directly induce pituitary LH secretion and synthesis mediated by AC/PKA, PLC/IP3/PKC, and Ca2+/CaM/CaMK-II pathways. Finally, estrogen treatment of prepubertal fish elicited increases in PrRPs and PrPR receptors expression in primary cultured grass carp hypothalamus cells, which further confirmed that the PrRP/PrRPR system may participate in the neuroendocrine control of fish reproduction. These results, taken together, suggest that PrRPs might act as a coupling factor in feeding metabolism and reproductive activities in teleost.

Prolactin-releasing peptide increases food intake and affects hypothalamic physiology in Japanese quail (Coturnix japonica)

Prolactin-releasing peptide (PrRP) increases food intake in birds, whereas it is a potent satiety factor in rodents and fish. The aim of this study was to determine the effects of central injection of PrRP on feeding behaviors and hypothalamic physiology in juvenile Japanese quail (Coturnix japonica). Intracerebroventricular injection of 1,692 pmol of PrRP increased food intake for the first 90 min after injection but did not affect water intake. Quail treated with PrRP displayed more food and drink pecks, less time standing but more perching, and decreased defecations. Prolactin-releasing peptide-injected quail had increased c-Fos immunoreactivity in the dorsomedial nucleus (DMN) and arcuate nucleus (ARC) of the hypothalamus. Hypothalamic neuropeptide Y receptor subtypes 2 and 5 and melanocortin receptor 4 mRNAs were greater in PrRP- than vehicle-injected quail. In the DMN, there was less corticotropin-releasing factor (CRF) mRNA and in the ARC, more CRF mRNA in PrRP- than vehicle-injected chicks. Thus, PrRP increases food intake in quail, which is associated with changes in hypothalamic CRF and neuropeptide Y receptor gene expression and c-Fos-immunolabeled cells in the ARC and DMN.

The effects of dietary macronutrient composition on lipid metabolism-associated factor gene expression in the adipose tissue of chickens are influenced by fasting and refeeding

Background

Broiler chickens are compulsive feeders that become obese as juveniles and are thus a unique model for metabolic disorders in humans. However, little is known about the relationship between dietary composition, fasting and refeeding and adipose tissue physiology in chicks. Our objective was to determine how dietary macronutrient composition and fasting and refeeding affect chick adipose physiology during the early post-hatch period.

Methods

Chicks were fed one of three isocaloric diets after hatch: high-carbohydrate (HC; control), high-fat (HF; 30% of ME from soybean oil) or high-protein (HP; 25% vs. 22% crude protein). At 4 days post-hatch, chicks were fed (continuous ad libitum access to food), fasted (3 h food withdrawal), or refed (fasted for 3 h and refed for 1 h). Subcutaneous, clavicular, and abdominal adipose tissue was collected for histological analysis and to measure gene expression, and plasma to measure non-esterified fatty acid (NEFA) concentrations (n = 6–10 per group).

Results

Adipose tissue weights were reduced in chicks that were fed the HP diet and adipocyte diameter was greater in the adipose tissue of chicks that ate the HF diet. Consumption of diets differing in protein and fat content also affected gene expression; mRNAs encoding fatty acid binding protein 4 and a lipolytic enzyme, monoglyceride lipase, were greater in chicks fed the HC and HF than HP diet in all three adipose tissue depots. Fasting influenced gene expression in a depot-dependent manner, where most fasting and refeeding-induced changes were observed in the clavicular fat of chicks that consumed the HC diet. Fasting increased plasma NEFA concentrations in chicks fed the HC and HP diets.

Conclusions

The decreased adipose tissue deposition in chicks fed the HP diet is likely explained by decreased rates of adipogenesis. Consumption of the HF diet was associated with greater adipose tissue deposition and larger adipocytes, likely as a result of greater rates of adipocyte hypertrophy. The depot-dependent effects of diet and fasting on gene expression may help explain mechanisms underlying metabolic distinctions among subcutaneous and visceral fat depots in humans.

Dietary macronutrient composition and central neuropeptide Y injection affect dietary preference and hypothalamic gene expression in chicks

OBJECTIVE

The objective of this study was to determine the influence of dietary macronutrient composition on central NPY's orexigenic effect in chicks.

METHODS

Day-of-hatch chicks were fed one of three diets (3000 kcal ME/kg) ad libitum from hatch: high carbohydrate (HC), high fat (HF; 30% ME derived from soybean oil), and high protein (HP; 25 vs. 22% CP). In Experiment 1, chicks received intracerebroventricular injections of 0 (vehicle), 0.2, or 2.0 nmol NPY on day 4 and food intake was recorded for 6 hours. In Experiment 2, chicks were given all three diets before and after injection. In Experiment 3, hypothalamus was collected at 1-hour post-injection for gene expression analysis.

RESULTS

The HC diet-fed chicks responded with a greater increase, while the chicks fed the HF diet had a lower threshold response in food intake to NPY. Neuropeptide Y dose-dependently increased food intake in chicks fed the HC and HP diets. Chicks administered 0.2 nmol NPY preferred the HC and HP diets over the HF diet. Relative quantities of hypothalamic NPYR1 and MC4R mRNA were reduced by NPY in chicks that consumed the HP and HC diets, respectively.

DISCUSSION

Consumption of the HC diet was associated with the most robust NPY-induced increase in food intake. Injection of NPY accentuated differences among dietary groups in hypothalamic gene expression of several appetite-associated factors, results suggesting that the NPY/agouti-related peptide and melanocortin pathways are associated with some of the diet- and NPY-induced differences observed in this study.