Biology Theses and Dissertations
Permanent URI for this collectionhttp://hdl.handle.net/1903/2749
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Item Subplate neurons and their role in the functional maturation of the brain(2016) Sheikh, Aminah; Kanold, Patrick O; Biology; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Normal brain development is crucial for the proper maturation of neural circuits and cognitive functioning. White matter brain injury during development results in disruption of normal brain maturation and consequently increases risk of developing disorders such as epilepsy and cerebral palsy. Crucial for the proper development of thalamocortical circuits are a transient population of neurons in the developing subcortical white matter of the brain referred to as subplate neurons (SPNs). SPNs are among the first cortical neurons to be born and are necessary for normal functional development of the cerebral cortex. This dissertation begins by studying the effect of SPN removal in the neonatal rat somatosensory cortex (S1). After subplate ablation in the S1 barrel region, we find that removal of SPNs prevents the development of the barrel field in L4, and in vitro recordings reveal that thalamocortical inputs to layer 4 neurons are weak. This dissertation then progresses to investigating the effects of a more clinically relevant and common brain injury among humans, neonatal hypoxia-ischemia (HI), which causes brain damage specific to different brain structures over development. In the preterm human, HI results in damage to subcortical developing white matter, referred to as periventricular leukomalacia (PVL). From other studies we know that HI can damage SPNs however, it is unclear how HI and its differing severities alters SPN circuits. This dissertation uses a rat model of HI in which either mild or moderate HI was induced at postnatal day (P)1. To investigate the functional synaptic connectivity changes of SPNs and layer 4 neurons in both injury categories, this dissertation also uses laser-scanning photostimulation (LSPS) combined with whole-cell patch clamp recordings in acute thalamocortical slices of rat A1 over development. Our results suggest that SPNs are uniquely susceptible to HI and that HI causes a rearrangement of SPN circuits. This leads to abnormal cortical function observed after HI. Results from these studies help fill in crucial gaps in the understanding of not only how important SPNs are in the proper development of multiple sensory regions, but also how vulnerable they are to hypoxic-ischemic brain injury.Item Development and plasticity of the functional laminar mesoscale organization of the primary auditory cortex(2016) Solarana, Krystyna; Kanold, Patrick O; Biology; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Early sensory experience is fundamental for proper structural and functional organization of the brain. A brain region that particularly relies on sensory input during a critical period of development is the primary auditory cortex (A1). The functional architecture of A1 in adult mammals has been widely studied on a macroscale and single-cell level, and it is evident that this sensory area is characterized by a tonotopic gradient of frequency preference and that individual auditory neurons are tuned to complex features of acoustic stimuli. However, the development of microcircuits within A1 and how experience shapes this mesoscale organization during different plasticity windows is not known. The work in this dissertation uses in vivo two-photon calcium imaging in mice to investigate how the population dynamics of auditory neurons within thalamorecipient layer 4 and supragranular layers 2/3 change over development – from before ear opening, through the critical period for auditory spectral tuning, and on to mature adult circuitry. Furthermore, this dissertation explores how brief visual deprivation has the power to initiate compensatory, cross-modal plasticity mechanisms and restructure network circuitry in the adult auditory cortex, after the critical period for developmental plasticity has closed. Results from these studies fill crucial gaps in our understanding of experience-dependent cortical circuit development and refinement by showing that the spatial representation of sound frequency is shaped by sensory experience, teasing apart the underlying laminar-specific differences in microcircuitry changes, and indicating an overall dissociation of plasticity of single-cell, mesoscale, and macroscale network properties.Item Development of Auditory Sensitivity in Barn Owls (Tyto furcata pratincola)(2014) Baxter, Caitlin S.; Carr, Catherine E.; Neuroscience and Cognitive Science; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)The development of hearing in the juvenile barn owl was investigated using tones (500 Hz to 12 kHz) and clicks of different rates (5-90 Hz). Auditory evoked potentials (AEPs) of the auditory nerve were recorded using the auditory brainstem response (ABR). Barn owl hearing matured in a similar trend to other developing vertebrates, including kittens, budgerigars, chickens, and gerbils. The onset of hearing began sometime earlier than the second week post-hatch, and proceeded in a frequency-dependent manner. Adult-like thresholds were reached in a progression from low to high frequency, and sensitivity was mature by P60. These patterns were consistent with CAPs recorded from juvenile barn owls in Europe. ABRs for clicks presented at 5-60 Hz demonstrated increasing amplitudes and decreasing latencies as barn owl chicks aged, while ABRs for clicks presented at 90 Hz were barely distinguishable between adults and juveniles.Item Developmental Alterations in Inhibitory Neurotransmission in the Fragile X Syndrome Mouse Basolateral Amygdala(2012) Kratovac, Sebila; Corbin, Joshua G; Biology; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Fragile X Syndrome, caused by Fmr1 gene inactivation, is characterized by symptoms including enhanced fear, hyperactivity, social anxiety, and autism, pointing to synaptic and neural circuit defects in the amygdala. Previous studies in Fmr1 knockout (KO) mice have demonstrated alterations in GABAA receptor (GABAAR) function in the basolateral amygdala during early postnatal development. In this study, we sought to determine whether these early defects in GABAAR function are accompanied by changes in protein expression of GABAAR alpha 1, 2, and 3 subunits, the pre-synaptic GABA-synthesizing proteins GAD65 and 67 (GAD65/67), and the post-synaptic GABAAR-clustering protein gephyrin. We found that the developmental trajectory of protein expression is altered in knockout mice for all tested proteins except GABAAR alpha 3 and GAD 65/67. Our results suggest that alterations in the timing of inhibitory synapse protein expression in early postnatal development could contribute to observed inhibitory neurotransmission deficits in the KO mouse basolateral amygdala.Item The Role of Water Quality in Beach Visitation Decisions in Croatia: Implications for Development of the Tourism Industry(2007-08-02) Dvarskas, Anthony Charles; Lipton, Douglas; Marine-Estuarine-Environmental Sciences; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Croatia is experiencing a surge in popularity as tourists are attracted to its pristine coastal waters. Although the growth of the tourism industry would bring increased revenues from visitation, the development of tourism could negatively impact the coastal resources. Worsening water quality could cause certain beaches, areas, or regions to become less desirable and consequently less likely to be visited. This study was designed to determine the role ofwater quality in tourists' decisions to visit beaches in Split-Dalmatia County and Krk Island using a conditional logit model. In addition to determining the role of water quality, this study used a multiple regression model to delineate the impact of changes in tourist numbers upon coastal water quality. As a final analysis, the findings from the economic conditional logit model were combined with an ecological multiple regression model in a 25-year dynamic model. Results of the conditional logit model indicated that water quality is positively and significantly related to the probability of a beach being selected by non-Croatian tourists in Split-Dalmatia County. Local perceptions of the safety of water for swimming also were significant predictors of the beach visitation decisions of non-Croatian tourists to Krk Island. The multiple regression model indicated that the presence of more tourists is significantly related to worse coastal water quality. Finally, the dynamic model indicated that higher numbers of tourists over time would eventually lead to higher total coliform levels and that beaches without sewage treatment or removal of total coliforms would experience a declining probability of selection by non-Croatian tourists over the 25-yr period. The dynamic model also indicated that driving tourists to a beach by addition of a Blue Flag may have unintended consequences in the absence of sewage treatment as the increasing numbers of tourists decrease the water quality and the probability of that beach being selected over the long term. These findings have important implications for policymakers and planners in Croatia, as the decision to pursue tourism growth without concomitant investments in sewage infrastructure may not be sustainable for the long term.Item Trade-offs within and between sexual traits in stalk-eyed flies (Diptera: Diopsidae)(2006-06-05) Fry, Catherine L; Wilkinson, Gerald; Behavior, Ecology, Evolution and Systematics; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)The allocation of limited resources to competing body parts during development may affect both the absolute and relative sizes of physical traits, creating potentially dramatic consequences for the evolution of morphology. While negative correlations between the sizes of body parts ("trade-offs") arising from the distribution of finite resources have long been anticipated, empirical support is relatively rare. In this study, I use two related species of stalk-eyed flies that differ in morphology to investigate whether eye-span exaggeration results in trade-offs with other body parts. One species, <em>Cyrtodiopsis dalmanni</em>, is sexually dimorphic, with males having exaggerated eye-span while the other, <em>C. quinqueguttata</em>, is sexually monomorphic with both sexes having approximately equivalent and relatively unexaggerated eye-span. I utilize complementary approaches including artificial selection, application of exogenous juvenile hormone, and diet manipulation to alter the absolute and relative length of the eye-stalks in order to reveal correlated changes in other physical traits. The results of these experiments suggest that exaggerated eye-span in male <em>C. dalmanni</em> is accompanied by a decrease in two other features of head morphology, eye-bulb size and eye-stalk width, as well as compromised testis growth and sperm production. No trade-offs were observed in females of either species or male <em>C. quinqueguttata</em>. These results are consistent with hormonally-mediated trade-offs arising from the allocation of limited resources to an exaggerated trait and suggest that those trade-offs may act as costs of developing exaggerated eye-span.