Hypothalamic Neuropeptide Y Expression in Normal and Aberrant Metabolic Homeostasis

Differential effects of neuropeptide Y and the mu-agonist DAMGO on 'palatability' vs. 'energy'

Differential effects of neuropeptide Y (NPY) and mu-opioid DAMGO on 'palatability' vs. 'energy'. A variety of studies suggest that NPY is an important manager of energy metabolism. In contrast, the opioid peptides appear to influence the 'rewarding' aspects of feeding. In the current study, we stimulated feeding by injecting NPY (110 pmol) or the mu-opioid agonist DAMGO (2 nmol) into the paraventricular nucleus of rats. Following injection, rats were given free access to laboratory chow and a 10% sucrose solution. Animals injected with saline derived 10% of their kilocalories from the chow and 90% from the sucrose solution (total kcal/4 h=12.2+/-1. 0). Those rats injected with NPY derived 48% of their energy from chow and 52% from the sucrose solution (total kcal/4 h=24.8+/-1.7). The DAMGO-injected rats derived only 15% of their kilocalories from chow and the remainder from the sucrose solution (total kcal/4 h=23. 0+/-2.3). Thus, while NPY and DAMGO both stimulated energy intake compared to saline controls (P<0.0001), the effect on intake of a palatable dilute energy solution (0.4 kcal/g) vs. a 'bland' laboratory chow (3.95 kcal/g) was different. The results of this study reinforce the notion that NPY has a major effect on energy needs, whereas opioids influence the 'rewarding' characteristics of foods.

Dissociated feeding and hypothermic effects of neuropeptide Y in the paraventricular and perifornical hypothalamus

The present study investigated the effects of neuropeptide Y (NPY) on food intake and body temperature (Tbo) in free-feeding unrestrained rats following injection into the medial hypothalamic paraventricular nucleus (PVN) or the lateral perifornical hypothalamus (PFH). NPY (78-235 pmol) or saline was infused unilaterally into the PVN or PFH in a volume of 0.4 microliter and simultaneous measures of food intake and Tbo were taken every 30 min for 3 h. Results indicated that NPY evoked changes in eating behavior and Tbo that were dependent upon the site of hypothalamic injection. Although PVN and PFH administration of NPY both increased food intake dose dependently within 30 min of treatment, PFH NPY-injected rats (n = 9) showed a stronger behavioral response compared to rats (n = 9) receiving NPY injections into the PVN. In PVN-treated rats, however, the increased eating was associated with a significant decline in Tbo evident within the first 30-min test interval. A mean maximal decline of 0.92 +/- 0.26 degree C occurred within 90 min of PVN treatment of the highest dose, which produced a reduction in Tbo that was maintained for 2.5 h. In contrast, NPY infusion into the PFH failed to reliably alter Tbo at any of the doses tested. These findings are consistent with evidence that NPY in the PVN and PFH may have distinct functions and suggest that although PFH NPY acts to stimulate a robust and relatively specific ingestive response, PVN NPY may participate in the complex integrative mechanisms responsible for the simultaneous regulation of feeding, thermoregulatory, and metabolic processes.

Neuropeptide Y: a central regulator of energy homeostasis

Neuropeptide Y (NPY) is a 36 amino acid peptide belonging to the pancreatic polypeptide family of neuroendocrine hormones. It is the most abundant peptide yet discovered in the mammalian brain and is widely expressed by neurons in the central and peripheral nervous systems as well as adrenal medullary cells. Recently, a large number of studies have focussed on the potential roles played by NPY within the hypothalamus and pituitary with respect to the control of food intake and energy homeostasis. It is now clear that NPY is a potent stimulator of food intake in models of hyperphagia, that hypothalamic NPY also regulates sympathetic neural activity and it appears that NPY may also influence the glucocorticoid, growth hormone and thyroid hormone axes. Taken together, current data suggest that hypothalamic and pituitary NPY-expressing cells represent an important and critical site of integration of peripheral hormonal signals with regulation of energy homeostasis.

Glucocorticoids are Required for Food Deprivation-Induced Increases in Hypothalamic Neuropeptide Y Expression

Neuropeptide Y (NPY), a 36 amino-acid peptide found within the hypothalamus, is thought to be an important regulator of food intake. Hypothalamic NPY gene expression, synthesis and secretion are all known to be increased in models of increased metabolic demand in which serum glucocorticoids are also elevated. The present studies were designed to test the hypothesis that glucocorticoids are required for increased hypothalamic preproNPY mRNA levels induced by food deprivation (FD). First, animals underwent bilateral sham-adrenalectomy (sham) or not (control), and were subjected to 72 h FD, or not. Total RNA was isolated from hypothalamic tissue blocks and the content of preproNPY mRNA was measured by solution hybridization/RNase protection analysis. This study revealed that there was no significant difference in hypothalamic preproNPY mRNA content between shamfed and control-fed groups, or between sham-FD and control-FD groups. In the second experiment, animals underwent bilateral adrenalectomy (ADX), were allowed to feed ad libitum and were sacrificed 1 day, 4 days and 7 days after ADX. Nuclease protection analysis revealed no significant effect of ADX on hypothalamic preproNPY mRNA levels over this time-course. Finally, we examined the role of glucocorticoids in regulating NPY gene expression following FD. Animals underwent bilateral ADX, or not. At the time of surgery, ADX animals received placebo, or corticosterone (B) replacement in the form of constant release pellets, at one of two doses. Food was removed from half of the animals in each group 24 h after surgery; all animals were sacrificed 72 h thereafter. There was no difference in preproNPY mRNA content between the ADX-FD and ADX-fed groups, relative to the fed controls. Replacement with corticosterone [ADX(B)] did not alter preproNPY mRNA content in fed animals, however preproNPY mRNA content in FD animals was increased 2.5-fold. These studies demonstrate that glucocorticoids are necessary and serve a stimulatory role in the increase in hypothalamic preproNPY mRNA levels observed under conditions of FD, and suggest that hypothalamic NPY gene expression may be directly responsive to peripheral metabolic and hormonal signals.

Developmental aspect of differences in hypothalamic preproneuropeptide y messenger ribonucleic Acid content in lean and genetically obese zucker rats

The genetically obese Zucker rat is a well characterized model of early onset human obesity. Many of the endocrine and metabolic abnormalities of obese animals are common to other strains of genetically obese animals as well as morbidly obese humans. Neuropeptide Y (NPY), a potent orexigenic agent, was recently found to be elevated in adult obese animals compared to their lean littermates. In this study we first examined hypothalamic expression of preproNPY mRNA, using solution hybridization/ nuclease protection analysis, in phenotypically-matched, i.e. lean or obese, immature (5-week-old) and mature (33-week-old) animals. Although changes were not statistically different, a trend toward decreased hypothalamic preproNPY mRNA levels was detected in both lean and obese mature animals. We next compared hypothalamic preproNPY mRNA levels between age-matched lean and obese animals at 5, 14 and 33 weeks of age and found elevated preproNPY mRNA levels in obese rats at all three ages. These data suggest that increased levels of hypothalamic NPY are an early manifestation of the obese phenotype and may, therefore, contribute to hyperphagia and increased weight gain in obese Zucker rats.