Matching Items (5)
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- All Subjects: Neurobiology
- Creators: Smith, Brian
Description
Specific dendritic morphologies are a hallmark of neuronal identity, circuit assembly, and behaviorally relevant function. Despite the importance of dendrites in brain health and disease, the functional consequences of dendritic shape remain largely unknown. This dissertation addresses two fundamental and interrelated aspects of dendrite neurobiology. First, by utilizing the genetic power of Drosophila melanogaster, these studies assess the developmental mechanisms underlying single neuron morphology, and subsequently investigate the functional and behavioral consequences resulting from developmental irregularity. Significant insights into the molecular mechanisms that contribute to dendrite development come from studies of Down syndrome cell adhesion molecule (Dscam). While these findings have been garnered primarily from sensory neurons whose arbors innervate a two-dimensional plane, it is likely that the principles apply in three-dimensional central neurons that provide the structural substrate for synaptic input and neural circuit formation. As such, this dissertation supports the hypothesis that neuron type impacts the realization of Dscam function. In fact, in Drosophila motoneurons, Dscam serves a previously unknown cell-autonomous function in dendrite growth. Dscam manipulations produced a range of dendritic phenotypes with alteration in branch number and length. Subsequent experiments exploited the dendritic alterations produced by Dscam manipulations in order to correlate dendritic structure with the suggested function of these neurons. These data indicate that basic motoneuron function and behavior are maintained even in the absence of all adult dendrites within the same neuron. By contrast, dendrites are required for adjusting motoneuron responses to specific challenging behavioral requirements. Here, I establish a direct link between dendritic structure and neuronal function at the level of the single cell, thus defining the structural substrates necessary for conferring various aspects of functional motor output. Taken together, information gathered from these studies can inform the quest in deciphering how complex cell morphologies and networks form and are precisely linked to their function.
ContributorsHutchinson, Katie Marie (Author) / Duch, Carsten (Thesis advisor) / Neisewander, Janet (Thesis advisor) / Newfeld, Stuart (Committee member) / Smith, Brian (Committee member) / Orchinik, Miles (Committee member) / Arizona State University (Publisher)
Created2013
Description
Olfaction is an important sensory modality for behavior since odors inform animals of the presence of food, potential mates, and predators. The fruit fly, Drosophila melanogaster, is a favorable model organism for the investigation of the biophysical mechanisms that contribute to olfaction because its olfactory system is anatomically similar to but simpler than that of vertebrates. In the Drosophila olfactory system, sensory transduction takes place in olfactory receptor neurons housed in the antennae and maxillary palps on the front of the head. The first stage of olfactory processing resides in the antennal lobe, where the structural unit is the glomerulus. There are at least three classes of neurons in the antennal lobe - excitatory projection neurons, excitatory local neurons, and inhibitory local neurons. The arborizations of the local neurons are confined to the antennal lobe, and output from the antennal lobe is carried by projection neurons to higher regions of the brain. Different views exist of how circuits of the Drosophila antennal lobe translate input from the olfactory receptor neurons into projection neuron output. We construct a conductance based neuronal network model of the Drosophila antennal lobe with the aim of understanding possible mechanisms within the antennal lobe that account for the variety of projection neuron activity observed in experimental data. We explore possible outputs obtained from olfactory receptor neuron input that mimic experimental recordings under different connectivity paradigms. First, we develop realistic minimal cell models for the excitatory local neurons, inhibitory local neurons, and projections neurons based on experimental data for Drosophila channel kinetics, and explore the firing characteristics and mathematical structure of these models. We then investigate possible interglomerular and intraglomerular connectivity patterns in the Drosophila antennal lobe, where olfactory receptor neuron input to the antennal lobe is modeled with Poisson spike trains, and synaptic connections within the antennal lobe are mediated by chemical synapses and gap junctions as described in the Drosophila antennal lobe literature. Our simulation results show that inhibitory local neurons spread inhibition among all glomeruli, where projection neuron responses are decreased relatively uniformly for connections of synaptic strengths that are homogeneous. Also, in the case of homogeneous excitatory synaptic connections, the excitatory local neuron network facilitates odor detection in the presence of weak stimuli. Excitatory local neurons can spread excitation from projection neurons that receive more input from olfactory receptor neurons to projection neurons that receive less input from olfactory receptor neurons. For the parameter values for the network models associated with these results, eLNs decrease the ability of the network to discriminate among single odors.
ContributorsLuli, Dori (Author) / Crook, Sharon (Thesis advisor) / Baer, Steven (Committee member) / Castillo-Chavez, Carlos (Committee member) / Smith, Brian (Committee member) / Arizona State University (Publisher)
Created2013
Description
Recent data suggests that olfactory input is important for antennal lobe development in honey bees. Chronic association of a single odor to food resources during crucial stages of development results in delayed antennal lobe development for mature foraging bees. The antennal lobes of these bees instead closely resemble an immature network observed in young, newly emerged bees. Using an odor stimuli variance assay, learning and memory tests can be used to explore how well honey bees discriminate single odors within complex odor mixtures. Here we are validating two different odor mixtures, a Brassica rapa floral blend and a second replicate mixture composed of common molecularly dissimilar odors. Odors in each mixture are either held constant or varied in concentration over 16 conditioning trials. Subsequent memory tests are performed two hours later to observe the ability of bees to distinguish and recognize specific odor components in each mixture. So far in our assay we find high rates of generalization for both odor mixtures. In general, more bees responded to all odors in the replicate treatment group over the Brassica treatment group. Additionally, bees in the Brassica treatment group did not respond to the target odor. More data is being collected to validate this assay. In future studies, I propose to apply this behavioral assay to bees with an altered olfactory developmental in order to see the functional impacts of this chronic odor association treatment.
ContributorsHalby, Rachael (Author) / Smith, Brian (Thesis director) / Jernigan, Christopher (Committee member) / School of Life Sciences (Contributor) / Barrett, The Honors College (Contributor)
Created2017-05
Description
Animals must learn to ignore stimuli that are irrelevant to survival, a process referred to as latent inhibition. The Amtyr1 gene has been shown through quantitative trait loci mapping to be linked to strong latent inhibition in honey bees. Here we implicate this G-protein coupled receptor for the biogenic amine tyramine as an important factor underlying this form of learning in honey bees. We show that dsRNA targeted to disrupt the tyramine receptors, specifically affects latent inhibition but not excitatory associative conditioning. Our results therefore identify a distinct reinforcement pathway for latent inhibition in insects.
ContributorsPetersen, Mary Margaret (Author) / Smith, Brian (Thesis director) / Wang, Ying (Committee member) / Sinakevitch, Irina (Committee member) / School of Life Sciences (Contributor) / Barrett, The Honors College (Contributor)
Created2016-12
Description
In the face of widespread pollinator decline, research has increasingly focused on ways that pesticides could be harming bees. Fungicides are pesticides that are used in greater volumes than insecticides, yet significantly fewer studies have investigated the effects of these agrochemicals. The fungicide Pristine® is commonly used on bee-pollinated crops and has been shown to be detrimental to physiological processes that are key to honey bee foraging, such as digestion and learning. This study seeks to investigate how Pristine® exposure affects the amount of water, nectar, and pollen that honey bees collect. Colonies were fed either plain pollen patties or pollen patties containing 23 ppm Pristine®. Exposure to fungicide had no significant effect on corbicular pollen mass, the crop volumes of nectar or water foragers, or the proportions of foragers collecting different substances. There was a significantly higher sugar concentration in the crop of Pristine®-exposed nectar foragers (43.6%, 95% CI [38.8, 48.4]) compared to control nectar foragers (36.3%, 95% CI [31.9, 40.6]). The higher sugar concentration in the nectar of Pristine®-treated bees could indicate that the agrochemical decreases sucrose responsiveness or nutritional status in bees. Alternatively, fungicide exposure may increase the amount of sugar that bees need to make it back to the hive. Based on these results, it would appear that fungicides like Pristine® do not strongly affect the amounts of substances that honey bees collect, but it is still highly plausible that treated bees forage more slowly or with lower return rates.
ContributorsChester, Elise (Author) / Harrison, Jon (Thesis director) / DesJardins, Nicole (Committee member) / Smith, Brian (Committee member) / Barrett, The Honors College (Contributor) / School of Life Sciences (Contributor)
Created2023-05