Prolactin-releasing peptide (PrRP) is an endogenous hypothalamic neuropeptide that when exogenously injected increases food intake in chickens, but decreases it in rodents and goldfish. We designed three sets of experiments to elucidate the mechanisms of PrRP's orexigenic effect in chicks. In experiment one, food and water intake were evaluated in chicks after receiving intracerebroventricular (ICV) injection of the vehicle, 0.75, 3, 12, 47 or 188 pmol PrRP. The administration of 12 and 47 pmol PrRP increased food intake for up to 120 min after injection, and 188 pmol increased it for up to 180 min. The lowest effective dose was 3 pmol, which increased food intake for up to 60 min after injection. Water intake was not affected. To investigate the molecular mechanisms, c-Fos immunohistochemistry was performed and mRNA expression of some appetite-associated neurotransmitters was measured in chicks that received either vehicle or 188 pmol of PrRP. The rostral paraventricular nucleus (PVN) was activated which coincided with increased neuropeptide Y (NPY) mRNA expression in the whole hypothalamus. In experiment two, food and water intake were evaluated in chicks fed a high carbohydrate (HC), high fat (HF) or high protein (HP) diet after ICV injection of vehicle, 3 or 188 pmol PrRP. Chicks fed the HP diet increased food intake at a lower dose than chicks fed HF and HP diets after ICV PrRP injection. In addition, ICV injection of vehicle, 3 and 188 pmol PrRP were performed in chicks fed all three diets, and ICV PrRP injection induced preferential intake of the HP diet over HC and HF diets. The expression of some appetite-associated neuropeptides in the hypothalamus was also measured in chicks fed the HC, HF or HP diet after ICV injection of vehicle or 188 pmol PrRP. There was a diet effect on mRNA abundance of all appetite-associated genes measured (P < 0.05), with greater expression in chicks fed the HF or HP than HC diet. While neuropeptide Y (NPY) mRNA abundance was similar between vehicle and PrRP-injected chicks that consumed HP or HF diets, expression was greater (P < 0.05) in PrRP- than vehicle-injected chicks that consumed the HC. In experiment three, the orexigenic effect of PrRP was tested in chicks selected for low (LWS) and high (HWS) body weight after central administration of vehicle, 24, 94 and 375 pmol PrRP. The LWS chicks had a lower threshold and higher magnitude of food intake increase in response to PrRP injection. Results demonstrate that PrRP is a potent orexigenic factor in chickens and that effects are likely mediated through the hypothalamus. The orexigenic effect of PrRP was influenced by dietary macronutrient composition, and diet in turn influenced the food intake response to PrRP. These results may contribute to a novel understanding of appetite regulation. / Master of Science

The objective of this dissertation research was to investigate the effect of dietary macronutrient composition on neuropeptide Y (NPY)-mediated regulation of adipose tissue physiology in broiler chickens during the early post-hatch period. A high-carbohydrate (HC), high-fat (HF) or high-protein (HP) diet was fed to broiler chicks in all experiments and various facets of physiology were evaluated at day 4 post-hatch, including diet-, fasting-, and neuropeptide Y-induced effects on gene expression, cellular morphology, and lipid metabolism. Experiment 1 was designed to study the effects of diet on molecular changes in different adipose tissue depots (subcutaneous, clavicular and abdominal) after 3 hours of fasting and 1 hour of refeeding. Adipose tissue weights were decreased in chicks that consumed the HP diet, whereas adipocyte diameter was increased in response to the HF diet. There was greater expression of mRNAs encoding fatty acid binding protein 4 (FABP4) and monoglyceride lipase in chicks fed the HC and HF diets than the HP diet in all three adipose tissue depots. Fasting increased plasma non-esterified fatty acid concentrations in chicks fed the HC and HP diets. Results suggest that the heavier fat depots and larger adipocytes in chicks fed the HF diet are explained by greater rates of hypertrophy, whereas the HP diet led to a decrease in adipose tissue deposition, likely as a result of decreased rates of adipogenesis. Experiments 2 and 3 were designed to investigate how dietary macronutrient composition affects the effect of centrally or peripherally administered NPY, respectively, on lipid metabolism-associated factor mRNAs in adipose tissue. In experiment 2, vehicle or 0.2 nmol of NPY was injected intracerebroventricularly (ICV) and abdominal and subcutaneous fat samples were collected at 1 hour post-injection. In the subcutaneous fat, ICV NPY injection decreased peroxisome proliferator-activated receptor gamma (PPAR gamma) and sterol regulatory element-binding transcription factor 1 (SREBP1) mRNAs in chicks fed the HF diet, whereas there was an increase in SREBP1 expression in chicks fed the HF diet after NPY injection. Expression of PPAR gamma and FABP4 mRNAs increased in the abdominal fat of HF diet-fed chicks after NPY injection. Thus, HF diet consumption may have enhanced the sensitivity of chick adipose tissue to the effect of centrally-injected NPY on gene expression of adipogenesis-associated factors. In experiment 3, vehicle, 60, or 120 micrograms/kg BW of NPY was injected intraperitoneally (IP), and subcutaneous, clavicular, and abdominal fat was collected at 1 and 3 hours post-injection. Food intake and plasma NEFA concentrations were not different among chicks fed the HC, HF or HP diet after IP NPY injection, indicating that the effects of NPY on adipogenesis were independent of secondary effects due to altered energy intake. In response to the lower dose of NPY, the expression of NPY receptor sub-type 2 mRNA was increased at 1 hour post-injection in the subcutaneous fat of chicks fed the HP diet, whereas there was less 1-acylglycerol-3-phosphate O-acyltransferase 2 mRNA in the subcutaneous fat of chicks fed the HC diet. The higher dose of NPY was associated with greater AGPAT2 mRNA in the clavicular fat of chicks that consumed the HP diet and less CCAAT/enhancer-binding protein alpha in the abdominal fat of chicks that were provided the HF diet. However, there was also a decrease in the expression of some of these factors, although mechanisms are unclear. In conclusion, dietary macronutrient composition influenced the response of adipose tissue to the adipogenic effects of NPY and metabolic effects of short-term fasting and refeeding during the first week post-hatch. Collectively, this research may provide insights on understanding NPY's effects on the development of adipose tissue during the early life period and mechanisms underlying diet-dependent and depot-dependent differences in adipose tissue physiology across species. / Ph. D.

The effect of the dietary macronutrient composition on weight loss has been a controversial issue for decades. During that time, a high-protein, high-fat, and low-carbohydrate diet has been one of the more popular weight loss diets with the public. We hypothesized that a computer simulation model using STELLA software could help to better understanding the effect of the dietary macronutrient composition on weight loss. We calculated daily total oxidation instead of total energy expenditure as others have done based on the facts that carbohydrate, fat, and protein intake influence carbohydrate, fat, and protein oxidation. In order to create a simple and accurate model comparing dietary macronutrient composition effects, we eliminated exercise as a factor and focused on a sedentary population. The model was validated by five sets of published human data. Following model validation, simulations were carried out to compare the traditional high-carbohydrate diet recommended by the American Dietetic Association and two well-known high-protein diets (Atkins and the Zone diet). The results of computer simulation suggested that the lean tissue retention effect of a high-protein diet, especially with a lower-fat diet, compared with a traditional high carbohydrate diet over 6 months.