Periodic Reporting for period 2 - GHRELMIGRA (The hormone ghrelin: Is it a key player in regulating performance, fuel metabolism and decision-making in migratory birds?)
Reporting period: 2020-06-01 to 2021-05-31
Understanding the mechanisms guiding migratory birds is a great challenge because of the complex arrays of internal and external factors that are involved. Understanding the physiological mechanisms underlying migratory behavior is a necessary step forsuccessful conservation strategies. This study also has translational implications, thanks to similarities in the molecular structure and biological functions of ghrelin in vertebrates.
The results obtained so far revealed that the gut-hormone ghrelin acts in the brain to affect decision-making and triggers departure movements in a migratory songbird. The impact of this discovery breaks new ground in the study of gut-brain communication in vertebrates. In human research, there has been growing interest in the role of ghrelin in appetite regulation during and after exercise. Results generated by this action might translate into new pharmacological and dietary approaches against obesity and metabolic syndromes and have profound societal implications in humans.
The results obtained so far revealed that the gut-hormone ghrelin acts in the brain to affect decision-making and triggers departure movements in a migratory songbird. The impact of this discovery breaks new ground in the study of gut-brain communication in vertebrates. In human research, there has been growing interest in the role of ghrelin in appetite regulation during and after exercise. Results generated by this action might translate into new pharmacological and dietary approaches against obesity and metabolic syndromes and have profound societal implications in humans.
At Western University (Canada), I used a climatic wind tunnel built for birds to mimic non-stop migratory flights in a captive environment. I also took advantage of an automated radio telemetry array - the Motus Wildlife Tracking - to track large-scale migratory movements. I used two species of American migratory songbirds, the Blackpoll Warbler and the Yellow-rumped Warbler (Setophaga coronata coronata). Below, I present the work performed and results achieved for each of three main research objectives.
1. Study of the effects of endurance flight on circulating ghrelin and contents of ghrelin in the stomach
In a laboratory experiment, I flew birds in the wind tunnel for different durations (0.5 to 6 hours) and measured circulating levels of ghrelin at the end of each test. To measure the effects of endurance exercise on ghrelin regardless of the effects of fasting, I then used the same birds to perform a fasting non-exercising test for the same duration as they previously flew. I collected stomach tissue and measured ghrelin contents in a subset of birds. Data analysis is in progress.
2. Study of how ghrelin regulates fuel metabolism during flights
In a laboratory experiment, I injected birds with ghrelin, flew them for different durations (0.5 to 4 hour) in the wind tunnel and measured circulating levels of a number of key metabolites to determine what nutrients the bird was using to fuel its flight. I measured triglycerides, as an indicator of fat accumulation, and β-hydroxybutyrate, fatty acids and glycerol as indicators of fat mobilization. I also measured uric acid (product of protein metabolism), and glucose. Laboratory metabolite analysis is completed. Data analysis is in progress.
3. Study of how ghrelin affects migratory behavior
In a field experiment, I caught migrating birds at a spring stopover site and radio-tracked their movements following ghrelin administration and release. I measured the effects of ghrelin manipulation on stopover duration, departure decisions and post-departure migratory behavior. Results of this study show that on the day of release birds treated with ghrelin advanced departure from the field site – the Old Cut Research station (Ontario, Canada), indicating that ghrelin affects departure decisions. Ghrelin manipulation did not affect stopover duration, departure time of the day, flight trajectories or overall post-departure migratory behaviour. This confirmed that our approach to ghrelin administration (single acute peripheral injection) does not produce long-term effects. The link between circulating ghrelin and decision-making in free-living birds suggests an important role of peripheral metabolic hormones in the control of bird migration and charts new horizons in the study of migration physiology.
In a laboratory experiment, I injected birds with ghrelin and used video cameras and infrared lights to monitor their behavior in cage for 3 days. I measured the effects of ghrelin manipulation on diurnal and nocturnal locomotor activity and feeding behaviour. I repeated this experiment during migratory and non-migratory seasons to investigate potential seasonal differences in ghrelin’s functions. Furthermore, I conducted a laboratory experiment to test the duration of ghrelin increase in blood upon experimental ghrelin administration. Data analysis is in progress.
The first scientific manuscript generated by this project, entitled “Experimental ghrelin administration affects migratory behaviour in a songbird” is currently under review in the journal Hormones and Behavior. Despite difficulties in disseminating research due to the outbreak of the COVID-19 pandemic, I worked to promote my work through oral presentations and fruitful discussions with peers, collaborators, students and the public. I presented my research at the event “Women in Ornithology” organized by CISO (Centro Italiano Studi Ornitologici) as part of the initiatives celebrating The International Day of Women and Girls in Science promoted by the United Nations. This event, which targeted the general audience and researchers, was broadcasted live from the CISO Facebook page. My presentation is available to everyone at https://ciso-coi.it/en/attivita/le-donne-nellornitologia/(opens in new window). I will also present the results generated by this project at three scientific conferences: the joint virtual meeting of the American Ornithological Society (AOS) and the Society of Canadian Ornithologists (SCO-SOC) in 2021, the International Symposium on Avian Endocrinology, Edinburgh, Scotland UK (ISAE) in 2022 and the Congress of the European Ornithologists’ Union, University of Giessen, Germany (EOU) in 2022.
1. Study of the effects of endurance flight on circulating ghrelin and contents of ghrelin in the stomach
In a laboratory experiment, I flew birds in the wind tunnel for different durations (0.5 to 6 hours) and measured circulating levels of ghrelin at the end of each test. To measure the effects of endurance exercise on ghrelin regardless of the effects of fasting, I then used the same birds to perform a fasting non-exercising test for the same duration as they previously flew. I collected stomach tissue and measured ghrelin contents in a subset of birds. Data analysis is in progress.
2. Study of how ghrelin regulates fuel metabolism during flights
In a laboratory experiment, I injected birds with ghrelin, flew them for different durations (0.5 to 4 hour) in the wind tunnel and measured circulating levels of a number of key metabolites to determine what nutrients the bird was using to fuel its flight. I measured triglycerides, as an indicator of fat accumulation, and β-hydroxybutyrate, fatty acids and glycerol as indicators of fat mobilization. I also measured uric acid (product of protein metabolism), and glucose. Laboratory metabolite analysis is completed. Data analysis is in progress.
3. Study of how ghrelin affects migratory behavior
In a field experiment, I caught migrating birds at a spring stopover site and radio-tracked their movements following ghrelin administration and release. I measured the effects of ghrelin manipulation on stopover duration, departure decisions and post-departure migratory behavior. Results of this study show that on the day of release birds treated with ghrelin advanced departure from the field site – the Old Cut Research station (Ontario, Canada), indicating that ghrelin affects departure decisions. Ghrelin manipulation did not affect stopover duration, departure time of the day, flight trajectories or overall post-departure migratory behaviour. This confirmed that our approach to ghrelin administration (single acute peripheral injection) does not produce long-term effects. The link between circulating ghrelin and decision-making in free-living birds suggests an important role of peripheral metabolic hormones in the control of bird migration and charts new horizons in the study of migration physiology.
In a laboratory experiment, I injected birds with ghrelin and used video cameras and infrared lights to monitor their behavior in cage for 3 days. I measured the effects of ghrelin manipulation on diurnal and nocturnal locomotor activity and feeding behaviour. I repeated this experiment during migratory and non-migratory seasons to investigate potential seasonal differences in ghrelin’s functions. Furthermore, I conducted a laboratory experiment to test the duration of ghrelin increase in blood upon experimental ghrelin administration. Data analysis is in progress.
The first scientific manuscript generated by this project, entitled “Experimental ghrelin administration affects migratory behaviour in a songbird” is currently under review in the journal Hormones and Behavior. Despite difficulties in disseminating research due to the outbreak of the COVID-19 pandemic, I worked to promote my work through oral presentations and fruitful discussions with peers, collaborators, students and the public. I presented my research at the event “Women in Ornithology” organized by CISO (Centro Italiano Studi Ornitologici) as part of the initiatives celebrating The International Day of Women and Girls in Science promoted by the United Nations. This event, which targeted the general audience and researchers, was broadcasted live from the CISO Facebook page. My presentation is available to everyone at https://ciso-coi.it/en/attivita/le-donne-nellornitologia/(opens in new window). I will also present the results generated by this project at three scientific conferences: the joint virtual meeting of the American Ornithological Society (AOS) and the Society of Canadian Ornithologists (SCO-SOC) in 2021, the International Symposium on Avian Endocrinology, Edinburgh, Scotland UK (ISAE) in 2022 and the Congress of the European Ornithologists’ Union, University of Giessen, Germany (EOU) in 2022.
Understanding the mechanisms guiding birds during migration is a great challenge because of the complex arrays of internal and external factors that are involved. This study will gather novel knowledge on how the ghrelin system affects decision-making, regulates appetite and fat metabolism, and responds to endurance exercise during migration. This will have immediate relevance for bird migration research. Understanding the physiological mechanisms underlying migratory behavior is a necessary step towards successful conservation strategies. Importantly, this study also has translational implications, thanks to similarities in the molecular structure and biological functions of ghrelin in birds and mammals. Knowledge gained on how ghrelin regulates fat metabolism and appetite during and after high endurance exercise in migratory birds might have a major socio-economic impact in the future in the veterinary field, animal husbandry and in the study of metabolic syndromes and eating disorders in humans.
Although the global pandemic situation has caused delay in the completion of some of the planned objectives, the results obtained so far revealed that the gut-hormone ghrelin acts in the brain to affect decision-making and trigger departure movements in a migratory songbird. The impact of this discovery breaks new ground in the study of gut-brain communication in vertebrates. The study of ghrelin in migratory birds, which have evolved incredible adaptations to manage energy, provides a new perspective in the study of how ghrelin and other gut hormones control appetite, energy balance and decisions in humans. This might translate into new pharmacological and dietary approaches against obesity and metabolic syndromes and have profound societal implications.
Although the global pandemic situation has caused delay in the completion of some of the planned objectives, the results obtained so far revealed that the gut-hormone ghrelin acts in the brain to affect decision-making and trigger departure movements in a migratory songbird. The impact of this discovery breaks new ground in the study of gut-brain communication in vertebrates. The study of ghrelin in migratory birds, which have evolved incredible adaptations to manage energy, provides a new perspective in the study of how ghrelin and other gut hormones control appetite, energy balance and decisions in humans. This might translate into new pharmacological and dietary approaches against obesity and metabolic syndromes and have profound societal implications.