Biology Theses and Dissertations
Permanent URI for this collectionhttp://hdl.handle.net/1903/2749
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Item Reactivation of plasticity in the adult visual cortex by control of neuronal excitability(2023) Borrell, Andrew; Quinlan, elizabeth; Biology; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Amblyopia is a highly prevalent form of monocular vision loss that impacts between 1-4% of the worldwide population. Amblyopia is characterized by decreased visual acuity in a single eye and is highly refractory to treatment past a “critical period” of heightened plasticity during early adolescence (>5 years of age). The time course of this critical period is due to the developmental regulation of experience-dependent synaptic plasticity in the primary visual cortex (V1). During early development, visual experience drives activity-dependent changes in NMDA-R subunit composition, refines the convergence of binocular inputs, and promotes the maturation of inhibitory circuits in V1. The transient conditions in V1 that permit the refinement of cortical circuits during the critical period also render V1 vulnerable to the detrimental impacts of amblyopia.The expression of critical period plasticity requires visual experience: dark-rearing delays the onset and closure of the critical period and prevents the experience- dependent change in NMDA-R subunit composition. It is now understood that visual experience in adulthood is also important for the expression of plasticity: sensory deprivation via prolonged dark exposure (DE) rejuvenates the V1 circuit to a juvenile-like state via a homeostatic increase in spontaneous excitatory in V1. Subsequent visual experience during light reintroduction (LRx) enables the expression of critical period plasticity and the functional rewiring of thalamocortical inputs to V1. Here I asked how the homeostatic increase in spontaneous activity induced during DE is regulated by visual experience immediately following LRx (LRxi), and during one day of subsequent day of LRx (LRxs). I demonstrate that the homeostatic increases in spontaneous excitatory neuron activity is maintained during LRxi and is accompanied by increased evoked excitatory neuron activity. These increases in averaged spontaneous and evoked activity returned to baseline by LRxs. Next, I asked whether decreased spontaneous activity following one day of LRx was necessary for the reactivation of critical period plasticity. Using the mouse model of ocular dominance plasticity (ODP) and cell-type specific expression of inhibitory chemogenetic Gi-DREADD receptors in fast spiking Parvalbumin-expressing interneurons, I demonstrated that prolonged disinhibition of spontaneous V1 activity during LRx occludes the reactivation of ODP, but not the reactivation of the plasticity of acuity. These results demonstrate the differing contribution of cortical mechanisms to ocular dominance versus acuity in the regulation of the critical period plasticity, and the necessity of the decrease in average spontaneous activity for the re-expression ODP.Item Cortical Contributions to a Combined Appetitive-Aversive Social Outcome Task.(2021) Schneider, Kevin N; Roesch, Matthew R; Neuroscience and Cognitive Science; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Learning through the emotional states of others is a critical skill for navigating our complex social environments, which is why it is a focal point of investigation in social neuroscience. Significant advances have been made in recent years, highlighting cortical brain regions where the transfer and processing of socially-derived affective information may be taking place. Among these regions are the anterior cingulate cortex (ACC) and orbitofrontal cortex (OFC), known for their roles in attention and valuation during decision-making tasks, respectively. However, social decision-making studies have typically focused on either reward or punishment as the outcome valence, making it difficult to determine the social specificity of neural contributions observed. Using a social task that manipulates reward and shock within the same experiment, I recorded single-unit activity from ACC and OFC in rats. I found that during the task, ACC activity shared responses for reward and shock outcomes, suggesting it encoded socially-derived information in the service of attention. OFC neurons showed responses to self and vicarious reward outcomes, consistent with previous work in primates. Interestingly, OFC also encoded the positive value of the rats’ approach to their conspecific following foot-shock delivery, which leads to stress relief and a reduced fear response. Thus, in this task, ACC and OFC encoded other-related outcome information with respect to the self, in accordance with their nonsocial functions, suggesting that during social decision-making tasks, internal state goals are prioritized when outcomes to the self are at stake.Item ARABIDOPSIS THALIANA GLUTAMATE RECEPTOR-LIKE 3.7 UNDERLIES ROOT MORPHOLOGY AND SIGNALING VIA MEMBRANE POTENTIAL HOMEOSTASIS(2021) Barbosa-Caro, Juan Camilo; Feijó, José A; Biology; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Plants perceive highly variable environments and biotic interactions through membrane receptors like the GLutamate Receptor-like (GLR) family, related to the ionotropic Glutamate Receptors that underlie information transmission in neurons. GLRs underpin information transduction and morphological adaptations in plants. However, mechanistic understanding is scarce. In Arabidopsis thaliana roots, we investigated how GLRs underlie amino acid-induced electric and Ca2+ excitability. We also assessed the contribution of GLR3.7 in root hair elongation. We present GLRs as mediators of a local, glutamate-induced electric and Ca2+ response in roots, with the same initiation kinetics of wound-induced Slow Wave Potentials (SWP). We identify GLR3.7 as mediator of root hair elongation through maintenance of membrane depolarization at the growing cell apex. These results propose a parallel between glutamate-triggered signals and SWP initial phase as local and chemically induced, and posit GLR3.7 as a possible contributor to Ca2+ homeostasis in root hair apical growth.Item LOCAL AND TOP-DOWN REGULATION OF OLFACTORY BULB CIRCUITS(2020) Hu, Ruilong; Araneda, Ricardo C; Neuroscience and Cognitive Science; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)The olfactory bulb (OB) is the first place in the brain where chemosensory processing occurs. The neurophysiological mechanisms underlying these processes are mostly driven by inhibition, which is implemented by a large population of local inhibitory neurons, and among them, the granule cell (GCs) is the most prominent type. Local inhibitory interneurons sculpt the coding of output neurons, affecting odor detection, discrimination, and learning. Therefore, the regulation of inhibitory circuits is critical to OB function and fine-tuning OB output. Specifically, inhibitory tone in the OB can be regulated by the dynamic interactions between cell-intrinsic factors affecting neuronal excitability and extrinsic top-down modulation associated with an animal’s behavioral state. Here, I provide new evidence for intrinsic mechanisms governing inhibitory interneuron excitability in the OB and how modulation by noradrenaline works in concert with these intrinsic mechanisms to affect circuit function. This work highlights circuit- and cell-specific differences in noradrenergic modulation with regards to short- and long-term plasticity within OB circuits.