Brandon A. Newmyer

Neuropeptide Y is associated with changes in appetite-associated hypothalamic nuclei but not food intake in a hypophagic avian model.

While neuropeptide Y (NPY) has been studied extensively per its pronounced role in food intake stimulation as well as its role in central pathways governing eating disorders, it has to our knowledge not been studied in polygenic models of hypo- and hyperphagia. Thus, the present study was designed to measure central NPY-associated food intake in lines of chickens that have undergone long-term genetic selection for low (LWS) or high (HWS) body weight and exhibit hypo- and hyperphagia, respectively. LWS chicks did not respond with any magnitude of altered food intake to any dose of NPY tested, while HWS chicks responded to all doses of NPY at similar magnitudes throughout the duration of observation. Both lines responded with similar increases in c-Fos immunoreactivity in the lateral hypothalamus and both divisions of the paraventricular nucleus; there were no significant line or line by treatment interactions. These data support the hypothesis that differences exist in the central NPY system of chicks from LWS and HWS lines and may provide novel insight for understanding NPY control of appetite.

The threshold of amylin-induced anorexia is lower in chicks selected for low compared to high juvenile body weight.

Chicks that have undergone long-term selection for low body weight responded to intracerebroventricular amylin injection with reduced food intake at a dose considerably lower and with a greater magnitude suppression than those selected for high body weight. Behaviors unrelated to ingestion were not affected. These data support the thesis of correlated amylin system responses to selection for low or high body weight, with possible implications to other species.

Neuropeptide AF differentially affects anorexia in lines of chickens selected for high or low body weight.

The recently discovered anorectic effect of neuropeptide AF (NPAF) has not been studied in hypo‐and hyperphagia animal models. The present study was designed to examine possible differences in appetite‐related effects after central NPAF administration in lines of chickens that had undergone long‐term divergent selection for low (LWS) or high (HWS) body weight and exhibit hypo‐ and hyperphagia, respectively. LWS chicks responded at a similar magnitude of food intake reduction to all doses of NPAF tested at all observation times. HWS chicks had an increased latency (150 min versus 30 min post injection) and an increased dose threshold of response (8 nmol versus 2 nmol) than LWS chicks. Water intake of LWS chicks was reduced in all doses tested at all observation times, whereas HWS chicks responded to the three doses of NPAF tested up to 60 min post injection, after which the decrease was sustained only at a dose of 8 nmol. In a comprehensive behaviour analysis, exploratory pecks, food pecks and locomotion were significantly reduced in both lines by NPAF, whereas sit time was increased in both lines. Other behaviours, including stand time, deep rest time and escape attempts, were not affected. These data suggest that the threshold of NPAF‐induced anorexia is lower in LWS than HWS chicks and that NPAF‐induced anorexia is a primary effect in both lines, and also support the hypothesis that differences exist in the central NPAF system between hypo‐ and hyperphagic individuals.

Stimulation of food intake after central galanin is associated with arcuate nucleus activation and does not differ between genetically selected low and high body weight lines of chickens

Galanin, a 29 residue peptide found in the hypothalamus, causes orexigenic effects in a variety of species. In the present study, we investigated appetite-associated effects of galanin in chicks from lines which have been selected from a common founder population for either low or high body weight. The low line consists of some anorexic individuals and there are obese individuals in the high line. Central galanin caused increased food intake in both lines with the magnitude of response similar in both lines. We also quantified the number of c-Fos immunoreactive cells in several hypothalamic nuclei that are associated with appetite. Only the arcuate nucleus had an increase in the number of reactive cells, a response that was similar for both lines. From these results we concluded that selection for body weight likely did not affect galanin function on induction of feeding in either lines, and that the effect of galanin is associated with arcuate nucleus activation in chicks.

Activation of murine pre-proglucagon–producing neurons reduces food intake and body weight

Peptides derived from pre-proglucagon (GCG peptides) act in both the periphery and the CNS to change food intake, glucose homeostasis, and metabolic rate while playing a role in anxiety behaviors and physiological responses to stress. Although the actions of GCG peptides produced in the gut and pancreas are well described, the role of glutamatergic GGC peptide–secreting hindbrain neurons in regulating metabolic homeostasis has not been investigated. Here, we have shown that chemogenetic stimulation of GCG-producing neurons reduces metabolic rate and food intake in fed and fasted states and suppresses glucose production without an effect on glucose uptake. Stimulation of GCG neurons had no effect on corticosterone secretion, body weight, or conditioned taste aversion. In the diet-induced obese state, the effects of GCG neuronal stimulation on gluconeogenesis were lost, while the food intake–lowering effects remained, resulting in reductions in body weight and adiposity. Our work suggests that GCG peptide–expressing neurons can alter feeding, metabolic rate, and glucose production independent of their effects on hypothalamic pituitary-adrenal (HPA) axis activation, aversive conditioning, or insulin secretion. We conclude that GCG neurons likely stimulate separate populations of downstream cells to produce a change in food intake and glucose homeostasis and that these effects depend on the metabolic state of the animal.

The Anorectic Effect of Neuropeptide AF is Associated with Satiety-Related Hypothalamic Nuclei

Neuropeptide AF (NPAF), a member of the RFamide family, is encoded by the same gene as neuropeptide FF (NPFF), which causes short‐term anorexia. However, reports on the role of NPAF on appetite‐related process are lacking. Thus, i.c.v. injections of 4.0, 8.0 and 16.0 nmol NPAF were administered to chicks to observe its effect on food and water intake. Chicks treated with 8.0 and 16.0 nmol i.c.v. NPAF decreased both their food and water intake. Additionally, all doses of NPAF injected caused a similar reduction in whole blood glucose concentration 180 min after injection. In a second experiment, chicks that received i.c.v. NPAF had an increased number of c‐Fos immunoreactive cells in the dorsomedial, paraventricular (magnocellular and parvicellular parts) and ventromedial nuclei. The arcuate nucleus and lateral hypothalamic area were not affected. In a third experiment, NPAF‐treated chicks exhibited fewer feeding pecks and spent less time perching, whereas they spent an increased time in deep rest. Other behaviours, including exploratory pecking, escape attempts, defecations, distance moved, and time spent standing, sitting and preening, were not affected by NPAF injection. We conclude that NPAF causes anorectic effects that are associated with the hypothalamus.

Both calcitonin and calcitonin gene-related peptides' thresholds of hypophagia are considerably lower in chicks selected for high rather than low juvenile body weight.

Effects of intracerebroventricular (ICV) injection of calcitonin (CT) and calcitonin gene-related peptide (CGRP) on food and water intake were measured in two lines of White Plymouth Rock chickens from a common base population that have undergone long-term divergent selection for either low (LWS) or high (HWS) juvenile body weight. These lines contain anorexic and obese individuals and serve as models for hypo- and hyperphagia. For both ICV injection of CT and CGRP, line HWS responded to a lower dose with decreased food intake than did line LWS. Both peptides were also associated with reduced water intake in both lines. Although plasma glucose concentrations were inherently different between lines, neither CT nor CGRP affected these levels. Comprehensive behavior analyses were conducted and only the number of food pecks was differentially suppressed between lines after both CT and CGRP injection. Thus, the selection program may have caused alterations in the endogenous CT and CGRP systems that synergistically, with other neurotransmitter systems, contribute to the role of food intake on the differential body weights between these lines.

Activation of Pyramidal Neurons in Mouse Medial Prefrontal Cortex Enhances Food-Seeking Behavior While Reducing Impulsivity in the Absence of an Effect on Food Intake

The medial prefrontal cortex (mPFC) is involved in a wide range of executive cognitive functions, including reward evaluation, decision-making, memory extinction, mood, and task switching. Manipulation of the mPFC has been shown to alter food intake and food reward valuation, but whether exclusive stimulation of mPFC pyramidal neurons (PN), which form the principle output of the mPFC, is sufficient to mediate food rewarded instrumental behavior is unknown. We sought to determine the behavioral consequences of manipulating mPFC output by exciting PN in mouse mPFC during performance of a panel of behavioral assays, focusing on food reward. We found that increasing mPFC pyramidal cell output using designer receptors exclusively activated by designer drugs (DREADD) enhanced performance in instrumental food reward assays that assess food seeking behavior, while sparing effects on affect and food intake. Specifically, activation of mPFC PN enhanced operant responding for food reward, reinstatement of palatable food seeking, and suppression of impulsive responding for food reward. Conversely, activation of mPFC PN had no effect on unconditioned food intake, social interaction, or behavior in an open field. Furthermore, we found that behavioral outcome is influenced by the degree of mPFC activation, with a low drive sufficient to enhance operant responding and a higher drive required to alter impulsivity. Additionally, we provide data demonstrating that DREADD stimulation involves a nitric oxide (NO) synthase dependent pathway, similar to endogenous muscarinic M3 receptor stimulation, a finding that provides novel mechanistic insight into an increasingly widespread method of remote neuronal control.

Neuropeptide SF is associated with reduced food intake in chicks

To our knowledge appetite-associated effects of neuropeptide SF (NPSF) are unreported. Thus chicks were intracerebroventricularly injected with 3.8, 7.5 and 15.0 nmol of NPSF and they reduced both their food and water intake. Blood glucose concentration was not affected. Additionally, NPSF-treated chicks did not exhibit any behaviors that were associated with stress or that may be competitive with ingestion. We conclude that NPSF is associated with anorectic and antidipsogenic effects.

The orexigenic effect of kyotorphin in chicks involves hypothalamus and brainstem activity and opioid receptors.

Kyotorphin (KTP), first isolated in the bovine brain and now having been identified in a variety of species, is known most extensively for its analgesic-like properties. KTP indirectly stimulates opioid receptors by releasing methionine enkephalin (met-enkephalin). Stimulation of opioid receptors is linked to hunger perception. In the present study, we sought to elucidate the effect of KTP on food intake in the neonatal chick. Intracerebroventricular injection of 0.6, 3.0 and 12 nmol KTP increased feeding up to 60 min post-injection. KTP treated chicks increased pecking efficiency and decreased time spent in deep rest, 20 and 30 min following injection, respectively. Gastrointestinal transit rate was not affected by KTP. Blocking mu, delta, and kappa opioid receptors suppressed orexigenic effects of KTP, suggesting that all three types are involved in KTPs stimulatory effect. The lateral hypothalamus (LH) and arcuate nucleus (ARC) of the hypothalamus and the nucleus of the solitary tract (NTS), within the brainstem had increased numbers of c-Fos immunoreactive cells following KTP treatment. In conclusion, KTP caused increased feeding in broiler-type chicks, likely through activation of the LH, ARC, and NTS.