Research in the Grippo Lab
From Larry Young & Todd Ahern, Emory University
In the Grippo Laboratory we use several different types of research techniques, including studying behavior, the endocrine system, the cardiovascular system, and the brain. Below you will find a description of some of our current research projects and several techniques that we employ in our studies. For more information about the research in the Grippo Lab, see our Publications and Presentations pages.
The Integration of Behavior, Physiology, and Neurobiology:
The Prairie Vole Model
A prairie vole family in their nest
Prairie voles are small rodents that look similar to mice (but have a shorter tail and flatter ears than mice). These rodents are interesting to us because they display social behaviors that are similar to humans. In their natural environment, these animals live in family groups, with a mother, father, and children all living together. Adult prairie voles form very strong social bonds (for instance, family bonds, opposite-sex bonds) that are difficult to break. Also, some (but not all) prairie voles mate monogamously, similar to the way humans mate. We study social behavior in the prairie voles, as well as how social experiences interact with other behaviors, the brain, endocrine system, immune system, and heart.
Click photos to enlarge
Current Research Projects
Mechanisms Underlying Negative Health Effects of Social Stress
Vicarious Stress, Behavior, and Endocrine Function
Stress seems to be an inescapable aspect of modern life. Whether it is worrying about your next test or the presentation that you have to give next week, our bodies are constantly in a state of high arousal. But what if you aren’t the one who is taking the test? What if it’s your significant other or friend who is experiencing stress? Can just being around or witnessing someone in a high-stress situation be enough to stimulate your own stress response? We are attempting to answer these questions by using prairie voles in a controlled laboratory setting. To do this, we will expose one of a sibling pair of voles to a stressor and allow the other animal to observe. It is our hypothesis that the animal that is observing the other animal in the stressful situation will exhibit higher than normal levels of circulating stress hormones, possibly as high as the animal actually undergoing the stressful situation. These findings would support the idea that the mere act of witnessing a stressful event or being around someone who is stressed can cause the observer to exhibit signs of stress. This project is being led by Josh Wardwell, a graduate student in the Neuroscience and Behavior training program.
Effects of Social Stress in Aging Animals
Social support has been shown to provide a buffer against negative effects of social and environmental stress such as impaired cardiovascular function, higher rates of depression and anxiety, and an increased stress response. However, there has been little research investigating this relationship in an aging model. To assess this long-term buffering effect, the highly social prairie vole is used as they are a socially monogamous species that tends to mate for life, similar to humans. Male and female prairie voles are paired together and allowed to breed until they reached old age and no longer are producing litters. Animals are then be placed into one of two conditions, an immediately stressed group or a socially isolated then stressed group. To assess the stress response of the animal, stress hormones are collected and compared across groups. We predict that aging animals that are socially isolated will show an increased stress response following a stressor compared to animals that have had constant social support from a partner. This current research project will help to shed more light on whether aging males and females respond differently to stress, and highlights the importance of social bonds and their beneficial effects against stress throughout the aging process. This project is being led by Wil Colburn, a graduate student in the Neuroscience and Behavior training program. (Picture from: http://traumatoolkit.blogspot.com/2011/11/hpa-axis-trauma-and-you.html).
Social Mechanisms Involved in the Link Between Mood and Cardiovascular Disorders
Oxytocin, Depression, and Cardiovascular Disease
Depression is an important risk factor for cardiovascular disease. Several changes are common to both these disorders, including increased heart rate and decreased variability in the interval between heartbeats. However, the mechanisms underlying this relationship are not well understood. The hormone oxytocin is thought to be involved in this association as it plays a role in both emotion/mood and cardiovascular homeostasis. Oxytocin has anti-stress properties and modulates several behaviors in both humans and non-human animals. Like humans, prairie voles develop depressive and anxiety behaviors and cardiac dysfunction when exposed to chronic isolation. Oxytocin levels are elevated in isolated voles and oxytocin treatment eliminates depressive behaviors and cardiovascular dysfunction in isolated individuals. To test the hypothesis that oxytocin may play a role in mediating the link between depression and cardiovascular disease, oxytocin receptors will be antagonized to determine if the lack of oxytocin receptor stimulation will increase susceptibility to the negative effects of prolonged social isolation. These experiments will provide valuable information about mechanisms underlying the link between cardiovascular disease and depression. This project is being led by Melissa-Ann Scotti, a postdoctoral researcher in the Department of Psychology.
Disrupting Social Bonds, Depression, and Autonomic Function
This research project is investigating the hypothesis that disruptions of the social environment will negatively influence both psychological and biological function. This experiment uses prairie voles as an animal model because social isolation in this species results in many depressive behaviors as well as disruptions in cardiac function; these same changes are observed in both depression and cardiovascular disease in humans. Adult male prairie voles will be implanted with a wireless radiofrequency transmitter to monitor cardiovascular function, and allowed fully heal. The male prairie voles will be paired with an adult female prairie vole; after five days, half of the males will be separated from the female partner, while the other half will remain paired (control) for an additional five days. The males will then undergo tests to assess how the animal copes when exposed to an inescapable stressor and a measure of the animal’s autonomic nervous system. This experiment will enable an investigation into behaviors, cardiovascular function, and autonomic nervous system function during the formation of a social bond and the disruption resulting from the loss of that bond. Using this animal model will help improve our clinical understanding and care for humans who are at risk for mood disorders and cardiovascular disease. This project is being led by Neal McNeal, a graduate student in the Neuroscience and Behavior training program.
Social Isolation and Blood Vessel Function
Social relationships positively influence psychological and biological function. The disruption of social bonds through separation or death often results in bereavement and can contribute to depression and cardiovascular disease. Social isolation in prairie voles results in depressive behaviors, increased heart rate, and autonomic imbalance. To date, the vascular system in prairie voles has not been investigated. In humans diagnosed with depression and/or cardiovascular disease, endothelial function and relaxation of the blood vessel wall are impaired, and these factors are associated with hypertension, atherosclerosis, and other cardiovascular risk factors. This project is investigating the hypothesis that social isolation produces disruptions in blood vessel contraction and relaxation. Future experiments will investigate blood pressure and cholesterol levels in the prairie vole to gain a comprehensive understanding of the cardiovascular consequences of social isolation. This project is being led by Melissa-Ann Scotti (postdoctoral researcher) and Neal McNeal (graduate student in the Neuroscience and Behavior training program), along with our collaborators from Midwestern University.
Prevention and Treatment of Social Stress-Induced Emotional, Cardiovascular, and Neurobiological Consequences
Effectiveness of Antidepressant Treatment for Social Isolation
The goal of this study is to investigate whether treatment with the antidepressant drug Zoloft can protect against deleterious cardiac and behavioral changes induced by social stress. This is an important consideration because isolation is associated with an increased mortality risk, especially in people with health issues such as cardiovascular disease. This investigation is the first to evaluate cardiac and behavioral responses to antidepressants in the context of social isolation using the prairie vole animal model. Therefore, this study will test the hypothesis that Zoloft treatment can improve measures of heart function and behavioral responses during stressors in socially isolated male prairie voles. This investigation and future similar projects will inform our understand of the mechanisms through which the brain changes during both stress and treatment. The novel experiments conducted in this animal model will improve our understanding of how negative social experiences adversely influence mood, cardiovascular regulation, and quality of life, and can lead to improved treatments for individuals experiencing social stress. This project is being led by Neal McNeal, a graduate student in the Neuroscience and Behavior training program. Thank you to Pfizer for the generous donation of the Zoloft (sertraline hydrochloride) used in this project! This donation was awarded to Neal McNeal, for use in his dissertation project. (Picture from: http://www.pfizer.com/products/product-detail/zoloft).
Treating Isolation with Environmental Enrichment
The disruption of social bonds in humans can significantly affect mental health, specifically mood and emotion. Environmental enrichment that stimulates the brain (such as cognitive activities and exercise) may be beneficial for individuals who suffer from the consequences of social isolation. This research project is investigating the hypothesis that environmental stimulation can protect against the negative effects of social isolation using prairie voles as an animal model. We are studying prairie voles in different social environments, with or without an enriched environment, and investigating depressive and anxiety behaviors, cardiovascular function, and central nervous system processes. This research can provide insight into whether stimulation from the environment can be helpful in preventing depression and anxiety symptoms and physiological consequences that result from social isolation or loneliness in humans. This project is being led by several current students in the lab.
Can Exercise Counteract Social Stress?
Disruption of the social environment has been shown to negatively affect psychological and physiological functions in humans and rodents. The focus of this study is to assess the degree to which exercise may counteract the negative effects of social isolation and stress on endocrine function, cardiovascular function and behavior. The animals used in this study are prairie voles, an extremely social rodent that provide an excellent translational model to investigate the effects of social stressors on behavior and physiology. To investigate this relationship, prairie voles are isolated from a same-sex sibling for a total of four weeks. Animals are exposed to chronic mild stress (CMS) for the last two weeks of this period. CMS includes several mild stressors (such as a foreign object in the animal’s cage or exposure to a strobe light), and is thought to mimic the daily hassles of human life that by themselves are insignificant but over time build up and become overwhelmingly stressful. Half of the prairie voles (experimental condition) will receive running wheels in their cages that can be voluntarily used for exercise and the other half will remain in standard housing. Behaviors related to depression, stress hormone levels, and cardiovascular regulation will be investigated to determine the extent to which exercise can be beneficial in animals exposed to social isolation and CMS. This experiment will further our understanding of the complex relationship between psychological and physiological health and provide insight for humans who find themselves in prolonged periods of mild stress. This project is being led by current Neuroscience and Behavior graduate students Wil Colburn, Neal McNeal, and Josh Wardwell.
Specific Research Methods
How to study "depression" in rodents?
We study several behaviors in the prairie voles, including behaviors that relate to depression and other mood disorders. For instance, the forced swim test is used as a measure of depressive behaviors in rodents. An animal is placed into a tank of water for a brief period, and its behavior is observed. Animals that respond in a passive manner to this test (for instance by floating instead of actively swimming around the tank) are showing a sign of depression. By observing the animal’s stress-coping strategies during this test, we are able to gain an understanding of its behavior. (Picture from: http://www.sciencedirect.com/
Elevated plus maze
We study behaviors related to anxiety in the prairie voles. The elevated plus maze is a plus-shaped maze that is elevated off of the ground. The maze has two opposing open arms of clear Plexiglas and two opposing arms that are protected by tall black walls. The animal is placed in the center of the maze and allowed to explore it for a brief period. We can then calculate the amount of time an animal spends in the open versus closed arms of the maze. Animals that are experiencing more anxiety spend little time exploring the open arms, and instead spend quite a bit of time in the closed, protected arms of the maze.
Cardiovascular and Autonomic Function
Using radiofrequency technology, we can study continuous cardiovascular and autonomic function in the prairie voles. After anesthetizing an animal, a small transmitter is implanted into its abdominal cavity. Leads from the device are positioned just below the surface of the skin to either side of the animal’s heart which gather and transmit cardiovascular data (using radio signals) to the computer. With this technology the computer creates an electrocardiographic (ECG) signal, allowing us to study the functioning of the heart. Because this technology is wireless, it is possible to study cardiovascular function in prairie voles during different behavioral tasks (such as the forced swim test or the elevated plus maze, described above). This can provide useful information about the integration of behavior and cardiovascular function.
Vascular and Endothelial Function
Blood vessel function
The functioning of the heart is directly related to the functioning of the blood vessels. Newer technology, involving the study of vascular contractions and relaxation ability, endothelial cell function, and blood pressure, can inform our understanding of how stress, behavior, and social experiences influence the progression of hypertension, atherosclerosis, or cardiovascular disease. (Picture credit: http://arterialhealth.net/physicians/physician-information/).
The immune system can be significantly affected by stress, behavior, and social experiences. Some of our studies include a focus on innate immunity or adaptive immunity. We can use these results to inform our understanding of both general immune function and specific immune system cells and factors that might be altered in the context of stress. (Picture credit: http://turtleresearch.files.wordpress.com/2011/08/dsc_0123.jpg).
Stress Hormones and Endocrine Function
Hormone levels in the circulation
Following behavioral procedures and physiological experiments, plasma can be analyzed for hormones and other chemicals associated with stress, behavior, emotion, and cardiovascular function. These analyses allow us to make inferences about the relative activity of those hormones and chemicals, and how they are influenced by behavior and the environment. For example, circulating corticosterone levels are used as an index of stress in rodents. This graph is showing higher corticosterone levels in prairie voles that have been exposed to social isolation (versus animals that are paired in a cage with a sibling), suggesting that isolated prairie voles are experiencing a higher level of stress.
Central Nervous System
Cells in the hypothalamus
In some studies, we analyze the functions of cells and neurotransmitters in the brain. Using antibodies, chemicals, and specific staining procedures, we can observe different cells in the brain of prairie voles that have been exposed to different behavioral tests or social situations. We can use this information to learn how the brain controls behavior or specific peripheral nervous system processes (such as cardiovascular function).
Example of an enriched environment
Environmental enrichment (EE) refers to creating a more complex habitat in which the prairie voles can live. EE can include toys, a larger cage, running wheels for exercise, social interaction, music, nesting material, as well as other items. Animals who live in an enriched environment will have increased synaptic activity. We have provided some of our voles with EE cages with the hypothesis that the enriched environment will help the prairie voles perform better on stress tests. We will compare isolated prairie voles in an enriched environment to isolated prairie voles in a standard lab cage to see if the EE group shows lower stress levels. We will also compare isolated prairie voles in EE cages to pair-housed voles to see if the enriched environment will provide some of the stimulation that the prairie voles miss when they are isolated.
Physical exercise may be protective for the body in many respects, including conferring benefits for our muscles, heart, and brain. Exercise may be a useful treatment for several conditions such as depression, anxiety, and heart disease. Using the prairie vole model, we are investigating the potential stress-buffering effects of exercise on behavior, the cardiovascular system, and the brain in the context of social stress. (Picture from: http://www.mindsparke.com/brain-training-blog/brain-exercises/brain-fitness-neurogenesis-and-social-contact/).
Many of our studies investigate specific behaviors in prairie voles. The study of exploratory behaviors can inform our understanding of an animal's willingness to investigate a novel environment. One example is the open field test, which can be used to study various behaviors such as general exploration, forward and backward motion, movements in the center section vs. surround section of the open arena, and grooming. In addition to exploration, the open field test can also provide insight into anxiety-related behaviors in prairie voles exposed to social stress.
To effectively study how stress might transmit vicariously between animals, our projects required the development of a novel testing apparatus. Most behavioral tests focus just on one animal at a time. For this study, we are interested in behavioral and physiological measures of stress response activation in two animals experiencing a stressor from two different perspectives (i.e., direct and observed). To accomplish this, we have combined two validated behavioral tests into a single testing apparatus, the tail-suspension test and the open field test. In the experimental group, one animal is directly exposed to a stressor (i.e., suspension by the tail for five minutes, the “model”) while another animal passively observes within the same testing apparatus (i.e., on the bottom of the open field chamber allowed to move around freely, the “observer”). The control group is identical to the testing group with the exception that the two animals are tested alone in separate apparatuses located within two different rooms. This paradigm allows us to draw strong conclusions, not only about the behavioral and physiological effects of vicarious stress, but also the stress attenuating effects of social buffering.