Biology Theses and Dissertations
Permanent URI for this collectionhttp://hdl.handle.net/1903/2749
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Item INTERACTIONS OF SOCIAL EXPERIENCE, ALCOHOL SENSITIVITY, AND THE SEROTONERGIC SYSTEM(2024) Ho, Ta-wen; Herberholz, Jens; Neuroscience and Cognitive Science; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Social isolation has been shown to correlate with increased alcohol consumption in various animal species. In humans, a decreased sensitivity to acute alcohol is correlated with future alcohol dependence and addiction. A plausible explanation for this correlation is that alcohol sensitivity decreases after isolation; however, our understanding of the mechanistic interaction between social isolation and sensitivity to acute alcohol is still in its infancy. The serotonergic system is one promising candidate that could be involved in this interaction because of its wide range of behavioral and physiological effects, especially those related to social experiences. In my dissertation, I investigated the roles of the serotonergic (5-HT) system with three separate aims: In the first aim, I measured the effects of several 5-HT agents (neurotoxin, reuptake blocker, and receptor agonist/antagonists) in freely-behaving crayfish that were communally housed (COMs) or individually isolated (ISOs) prior to ethanol (EtOH) exposure. I found that 5-HT is important in regulating the social differences in EtOH sensitivity, and 5-HT2βPRO receptors emerged as candidates to produce this interaction between 5-HT and EtOH. My results from this aim suggest that these receptors are downregulated in isolated crayfish, leading to reduced behavioral EtOH sensitivity. The second aim employed single-cell neurophysiology and pharmacology in the lateral giant (LG) circuit of reduced ex vivo crayfish preparations to investigate the cellular-molecular mechanisms that underlie the interaction between 5-HT and specific EtOH receptor targets. I found that the LG neurons are stimulated by EtOH, and social differences in EtOH sensitivity between COMs and ISOs are paralleled at the level of these single neurons. Specifically, my results suggest that social isolation causes downregulation of 5-HT2βPRO receptors and 5-HT1αPRO receptors on the LG neurons and upregulation of these receptors subtypes in GABAergic neurons that send feed-forward inhibition onto the LG neurons. In my third aim, I developed a wearable, miniature, cyclic voltammetry device that is capable of detecting (injected) monoamine neurotransmitters (including 5-HT) in freely-behaving crayfish. With improved sensor sensitivity in the future, this will allow measurements of 5-HT release patterns in crayfish with different social histories, including during EtOH exposure. Together, the results from my dissertation will inform work in other model systems and improve our understanding of the interactions between social experience, the 5-HT system, and alcohol use.Item SEX-SPECIFIC EFFECTS OF PATERNAL DEPRIVATION ON HYPOTHALAMIC NEUROIMMUNE RESPONSE AND GENERAL ANXIETY-LIKE BEHAVIOR IN PEROMYSCUS CALIFORNICUS (CALIFORNIA MICE)(2021) Walker, Shakeera; Glasper, Erica R; Neuroscience and Cognitive Science; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Early-life stress (ELS) can induce anxiety-like behaviors and social deficits in male and female rodent models via neuroinflammation. The California mouse (Peromyscus californicus) is a rodent model for paternal deprivation (PD), a form of ELS. The paternal California mouse is essential in offspring development; his absence impairs emotional regulation and induces sex-specific deficits in social behaviors and neuroplasticity. We determined to what extent PD induced sex-specific social and anxiety-like behaviors in adult California mice during the three-chamber social interaction test and the novelty-suppressed feeding test. We also assessed the neuroinflammatory response to PD in the same mice after an acute physical stressor. We demonstrated that female California mice displayed social avoidance, while PD males exhibited stress-induced eating in novel anxiogenic environments. PD also increased hypothalamic interleukin-1β, but only in adult males. Taken together, PD resulted in sex-dependent stress-coping behaviors, which may underlie sex differences in neuroinflammatory responses in adulthood.Item Auditory Processing of Sequences and Song Syllables in Vocal Learning Birds(2021) Fishbein, Adam; Dooling, Robert J; Neuroscience and Cognitive Science; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)The ability to use speech and language is at the core of what it means to be human. How our brains manage this cognitive feat and how it evolved in our species remain mysterious, in part because of how unique speech and language seem to be. We are the only primates who can produce learned vocalizations, but vocal learning is widespread among songbirds and parrots. Just like us, those birds rely on auditory perception to learn their songs and extract information used for communication. Studies using vocal learning birds can thereby help us understand how the brain processes vocal signals and why species differ in vocal communication abilities. But while the melodic patterns of birdsong are striking to the human ear, we cannot assume that song sequences are perceived that way by the birds, nor that the features birds hear are detectable by us.In this dissertation, I investigate how songbirds (focusing on the zebra finch (Taeniopygia guttata)) and parrots (focusing on the budgerigar (Melopsittacus undulatus)) process the sequential patterns and syllable-level details of birdsong, using behavioral auditory discrimination experiments and neurophysiological recordings in the central auditory system. The results show the following: 1) zebra finches and other songbirds are much more sensitive to changes in individual elements than changes in sequence, 2) budgerigars are better than zebra finches at hearing sequence changes but are also limited in their abilities compared to humans, 3) zebra finches are highly sensitive to the acoustic differences in utterances of the same motif syllables, 4) the budgerigar central auditory system encodes sequence more strongly in some respects than the zebra finch central auditory system, and 5) both the zebra finch and budgerigar central auditory systems can encode the rapid acoustic details of sounds well beyond human hearing abilities. Together, these findings indicate that vocal learning birds may communicate more at the level of syllable details than through sequential patterns, in contrast to human speech. The results also show neurophysiological species differences in sequence processing that could help us understand the differences between humans and other primates in vocal communication.Item MOVEMENT ECOLOGY OF THE MEXICAN FISH-EATING BAT, MYOTIS VIVESI(2020) Hurme, Edward; Wilkinson, Gerald S; Biology; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Foraging behavior is influenced by the distribution of prey in time and space and the presence of conspecifics. Echolocating bats, which advertise their behavior while vocalizing, provide a unique opportunity for understanding how an organism interacts with conspecifics and the environment to find food. Here I use GPS tracking combined with on-board recording to investigate the foraging movements of lactating Mexican fish-eating bats, Myotis vivesi, in the Gulf of California, Mexico, over a 5-year period. In Chapter 1, I assessed five alternative methods for behavioral state segmentation of GPS tracked foraging paths using on-board audio for validation. While most methods perform well, hidden-Markov model segmentation showed the highest accuracy at predicting foraging movement. In Chapter 2, I evaluated habitat selection across multiple scales for fish-eating bats foraging in the Midriff Islands Region in the Gulf of California. Foraging site use at large scales is most predictive and is associated with dynamic (chlorophyll concentration) and static variables (ocean depth, sea floor slope) consistent with known tidal upwelling regions. In Chapter 3, I examine the function of in-flight social calls recorded from roughly half of all tagged individuals during their foraging flights. Calls contained spectral differences among individuals, were associated with the ends of flights as bats return to their roost, and increased in occurrence with pup age, consistent with directive calls used to communicate with mobile pups. In Chapter 4, I explore how prey distribution impacts social behavior and foraging movements. On-board audio reveals that conspecifics are present during commuting and foraging and playback experiments demonstrate an attraction to foraging call sequences. In collaboration with several colleagues I combined these findings with data from four other bat species ranging in diet and habitat type. Taken together, bat species that frequently encounter conspecifics, such as Myotis vivesi, have ephemeral prey and variable flights (e.g. duration and foraging site location), whereas bats that forage solitarily have predictable or non-shareable prey, such as a congener Myotis myotis, show less variability in their flights. Overall, these results provide new insights into the foraging dynamics and social behavior of bats.Item SOCIAL STRUCTURE OF ASIAN ELEPHANTS (ELEPHAS MAXIMUS) IN SRI LANKA(2015) Samy, Julie Marie; Wilkinson, Gerald S; Thompson, Katerina; Biology; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Asian elephants (Elephas maximus) are critically endangered and live in fragmented populations spread across 13 countries. Yet in comparison to the African savannah elephant (Loxodonta africana), relatively little is known about the social structure of wild Asian elephants because the species is mostly found in low visibility habitat. A better understanding of Asian elephant social structure is critical to mitigate human-elephant conflicts that arise due to increasing human encroachments into elephant habitats. In this dissertation, I examined the social structure of Asian elephants at three sites: Yala, Udawalawe, and Minneriya National Parks in Sri Lanka, where the presence of large open areas and high elephant densities are conducive to behavioral observations. First, I found that the size of groups observed at georeferenced locations was affected by forage availability and distance to water, and the effects of these environmental factors on group size depended on site. Second, I discovered that while populations at different sites differed in the prevalence of weak associations among individuals, a core social structure of individuals sharing strong bonds and organized into highly independent clusters was present across sites. Finally, I showed that the core social structure preserved across sites was typically composed of adult females associating with each other and with other age-sex classes. In addition, I showed that females are social at all life stages, whereas males gradually transition from living in a group to a more solitary lifestyle. Taking into consideration these elements of Asian elephant social structure will help conservation biologists develop effective management strategies that account for both human needs and the socio-ecology of the elephants.