Zoe R. Donaldson, Ph.D. - US grants

Project Summary Social bonds between family members and friends can last a lifetime. As long as these attachments exist, the selective motivation that drives us to seek out and interact with these individuals represents a healthy, reinforcing mechanism that maintains these bonds. But what happens to these motivational systems when a bond is permanently lost? Most people eventually learn to adapt to the loss of a loved one, but for some, the failure to adapt leads to function-impairing grief that can last years. Clinically, this is known as complicated grief. Despite the central importance of socio-motivational processes and their appropriate transformation following loss, their neuronal basis remains unclear. To address this deficit, I propose to use monogamous prairie voles, which form life-long bonds and exhibit distress following separation from their partner. Pair-bonded prairie voles will lever- press to be reunited with their partner, enabling us to quantify bond-directed motivation. My lab is developing a high-throughput operant system to quantify bond-directed motivation. I will combine this novel behavioral paradigm with advanced neurogenetic tools to interrogate the neuronal substrates of bond-directed motivation. I will test whether bond strength predicts levels of partner-directed motivation and how quickly this motivation extinguishes following permanent partner separation. Then, using our operant paradigm in combination with in vivo Ca2+ imaging and cell-specific manipulations of neuronal activity, I will test the hypothesis that distinct neuronal populations within reward-related brain regions modulate partner-directed motivation. Finally, because some people experience pathological forms of grief characterized by persistent dwelling on the lost bond, I will ask whether artificially reactivating the neuronal ensemble that encodes a pair bond leads to prolonged motivational responses following bond loss. Completion of these experiments will provide fundamental insights into the engagement of social motivation systems at a neuronal level ? both when a bond remains intact and following its disruption. There is a pressing need for this research; there are no currently accepted paradigms for studying selective social motivation or the emotional response to loss. As the U.S. population ages, there will be a substantial public-health burden from increased rates of bereavement-induced mental illness, heart disease, and complicated grief, and this work represents a means to elucidate important biological mechanisms that contribute to these phenomena.

Abstract: Attachment powerfully shapes our development and remains a primary driver of health and well-being in adulthood; disruption of attachments is highly traumatic. While affiliation, defined as general positive social interactions, is shared widely among mammals, attachment, or selective affiliation as a result of a bond, is far rarer and of primary relevance to humans. While affiliation has been studied in a number of contexts, how the neural circuitry that underlies affiliation ultimately contributes to adult attachment remains largely unknown. In this proposal, we will take a comparative framework to understand how the basic circuitry and neuronal patterns that underlie non-selective affiliation are ultimately engaged and underlie selective attachment in adulthood. Specifically, we will examine how the neurobiology of affiliative behavior in mice has been elaborated to support the more complex attachments formed by monogamous prairie voles and gregarious fruit bats, representing a spectrum of social relationships. We will focus on the hippocampal CA2 region as it has been shown to play a specialized role in social behavior and receives direct inputs from oxytocin and vasopressin producing cells in the paraventricular hypothalamus. Specifically, we will test the overarching hypothesis that CA2 population activity patterns follow similar trajectories across species before and during mating, and subsequently diverge to causally drive affiliative investigation in mice (Golshani/Hong) and different forms of attachment in prairie voles (Donaldson) and bats (Yartsev). To test this hypothesis we will refine and use new generation open-source wireless miniaturized microscopes (Aharoni) that will allow prolonged recordings of large neuronal populations in freely behaving animals. Kennedy will bring computational expertise and allow a unified data analysis framework cross species. In Aim 1 we will perform in-vivo calcium imaging in mice, prairie voles and bats to test the hypothesis that mating experiences modulate CA2 neural dynamics and that CA2 activity patterns encode spatial and identity information. We hypothesize that species that form attachments to mating partners, activity patterns will differentiate preferred vs. non-preferred partners. In Aim 2 we will use chemogenetic inhibition of CA2 in all species to determine whether CA2 causally drives affiliative and attachment behaviors. In Aim 3 we will test the hypothesis that inhibition of vasopressin inputs to CA2 will reduce the dimensionality of CA2 population activity patterns after mating, diminish memory of the mate in all species, and in voles and bats, reduce the decodability of the identity of the previous mating partner. In a technology development aim, we will develop and test a ?true wireless? digital data transmitting microscope with power over distance charging capability that will allow prolonged imaging over many hours without human intervention.