Hungry, stressed chicks? Understanding Hypothalamic Regulation of Appetite in Birds

Lead Research Organisation: University of Edinburgh
Department Name: The Roslin Institute

Abstract

Early life is extremely important time of life and stress experienced as a developing embryo can have lifelong consequences. In birds, exposing an incubating mother or developing egg to stressful stimuli can change survival, breeding success, productivity, health and welfare of the offspring. Appetite and body weight are closely regulated by the nervous and endocrine systems and these systems are particularly vulnerable to stress. In this project we will investigate the neurobiological mechanisms of early life stress programming on brain feeding circuits. The aim is to determine how appetite is developed in birds and how it is affected by pre-natal stress.

Feeding circuits in the bird brain are established during the second half of embryonic development and they achieve their characteristics 1 to 2 days before hatch. Although the development of the neural circuit formation is largely undetermined in birds, brain growth is largely complete before hatching in species, such as quail, where the young are relatively mature and mobile from hatch. As these neural circuits appear to develop rapidly and need to become functional after hatch, we hypothesise that brain feeding circuits are especially vulnerable to stress hormones during development. Here we will investigate whether this results in permanent dysregulation of brain circuit function leading to changes in post hatch characteristics.

We will investigate the changes in functional brain activity and behaviour across early life when avian brain circuits are actively developing and forming connections. We will also examine whether embryos and chicks exposed to early life stress have differences in their feeding circuits as we know from our previous work that they have lower body weights as adults. We will increase levels of stress hormone (corticosterone) to naturally occurring high levels by injecting corticosterone into fertilised quail eggs. This mimics the stress hormone signal that stressed mothers deposit into the egg (quail early life stress programming model). All our studies will be performed in both male and female quail as there is evidence to suggest there are sex differences in appetite regulation.

1. We will map the functional feeding (hunger and satiation), pathways within the normal bird brain and subsequently in brains exposed to prenatal corticosterone by using a marker of neuronal activation. We will identify whether the cells increase or decrease appetite. We will also investigate whether early life stress affects feeding behaviour and the general movement of the chicks once they have hatched.

2. We will examine whether the key hormone and neural circuits, that regulate appetite, are changed in embryos and chicks that have been subjected to early life stress programming by quantifying the gene expression.

3. Using a technique to record electrical impulses of the feeding circuits in the brain called electrophysiology, we will investigate whether early life stress changes the sensitivity of cells in the feeding circuit to glucose. Brain cells that detect changes in glucose inform the brain of the metabolic needs of the body. Interestingly, the glucose levels measured in brain fluid of birds are several fold higher than in mammals indicating that glucose regulation may be more important in birds.

We have developed a novel brain slice preparation for quail embryo and chick and are (to our knowledge) the only lab in the UK currently able to do this. We will provide novel data on the sensitivity of the bird brain to glucose and quantify if there are changes in the cells properties and actions.

These studies are important as they will provide unique information into the brain mechanisms that regulate appetite in newly hatched chicks and elucidate the mechanisms by which early life stress may program the feeding circuits in the brain.

Technical Summary

We will provide important, novel information on how appetite is regulated during early life in male and female birds and investigate how hypothalamic feeding circuits may be programmed through early life stress. In addition to fundamental research on avian homeostasis regulation, the project will provide valuable information for industrial stakeholders in relation to the management of eggs and chicks.

We will perform a rigorous neurophysiological investigation into the developmental sequelae of changes in functional brain activity, regulatory feeding pathways and neuropeptide activity and feeding related gene expression in the quail brain using a combination of techniques that include immediate early gene mapping with immunohistochemistry, behavioural measurements, RT-qPCR and brain slice electrophysiology.

Our pilot data show that stress hormones play a permissive role in causing dysregulated feeding behaviour in birds as stress in early life leads to a reduction in body weight. Feeding is exquisitely regulated by a network of discrete hypothalamic nuclei that respond to metabolic signals from the body. Many of the neurochemical signals used to signal stress are the same signals used by the brain to indicate hunger/satiety and to control the early development of the hypothalamus. Surprisingly, the neurobiological mechanisms by which prenatal stress programmes appetite neural circuits to cause reduced weight is unknown. Understanding these mechanisms is critical because it could provide the opportunity for intervention strategies to improve chick health, welfare and growth.

We will use an established avian model of developmental programming in Japanese quail to investigate the neurobiological molecular and cellular mechanisms underlying early life stress programming. We hypothesise that hypothalamic feeding pathways are especially vulnerable to excess stress hormones at a time when brain circuits are actively developing and forming connections.

Planned Impact

Who will benefit and why:

Immediate beneficiaries:
Scientists whose research is in the field of early life stress programming, central mechanisms regulating feeding and energy homeostasis, developmental neuroscience and neuroendocrinology. Our study will provide technological advances for avian electrophysiology in the UK. It is the only known facility in the UK that can perform neuroendocrinological electrophysiology in birds. It will contribute to the development of tools and techniques to help others carry out research on the nervous system in birds. Our findings, published in high impact journals, will benefit those managing commercial hatcheries, bird breeders to those in industry interested in stress and food intake in birds. Scientists will also benefit from the avian technology training workshop that will enhance the research capacity and knowledge of UK and International scientists (through current BBSRC Japan partnering award) in an emerging discipline. The topics of food intake, stress and animal welfare are of great interest to the public and our research will be widely communicated to the public through engagement activities.

Life-long learning of skills and training:
The development of novel embryo and chick brain slice preparations to study functional neurophysiology during neurodevelopment using in vitro electrophysiology with the capability to use single cell RT-qPCR technologies is a methodological advance for bird research both in the UK and globally. Its potential uses in studying other behaviours in birds go well beyond its initial development so there is a huge practical gain. The next generation of scientists will be trained in in vivo skills, animal physiology, electrophysiology, avian behavioural research and public engagement.
We will retain a highly skilled electrophysiologist - a critically limited resource in the UK and internationally, who will also benefit from the training provided in related research techniques such as avian behavioural research through to molecular discovery techniques such as RT-qPCR. Post graduate and undergraduate students, collaborators and visitors (including international) will be trained. Increased future employability within and outside the scientific sector will result due to training in transferable and professional skills, including public engagement.

Improving animal lives and health:
This research fits squarely into the BBSRC's strategy to fund innovative research that tells us how the brain controls behaviour and improvement of avian health and welfare including agricultural animals. Our multidisciplinary research will advance understanding of the interaction of key neuroendocrine signals and neural circuits with particular emphasis during periods of neurodevelopment. If we understand how the brain is altered as a result of stress hormones through activation of the stress axis and how this system interacts with the feeding circuit that is especially vulnerable to stress, it will shed light on how phenotype e.g body weight is regulated during normal life and during times of stress. This will lead to new strategies or allow objective assessment of existing control strategies as alternative means of controlling stress or body weight in birds. Our results could potentially lead to significant economic benefits and improve the welfare of billions of poultry for which there is a real need.

Industrial Stakeholders:
In addition to fundament research on avian homeostasis regulation, the project will provide valuable information for real application for industrial stakeholders to improve the management and welfare of eggs and chicks in the poultry incubation and hatchery industry. We will engage with industrial stakeholders yearly throughout the grant. We have a stake holder workshop planned in the final year to ensure that interested parties are updated with our final findings and conclusions in order to help inform policy going forward.

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