Showing 1 - 50 of 116 Items

Date: 2019-05-01

Creator: Casey Breslow

Access: Open access

Modulation in neural systems is important for regulating physiology and behavior (Wright et al., 2010). Peptides, hormones, and amines are common neural modulators, acting on many neural systems across species. One group of neural networks that can be regulated are central pattern generators (CPGs), which generate rhythmic neural patterns, which drive behaviors (Marder and Bucher, 2001). Octopamine, and its precursor tyramine, are two amines that have been found to regulate (CPGs) across species (Cooke, 2002; Fussnecker et al., 2006). One role of octopamine in the decapod neurogenic heart is regulating the frequency and the duration of heart beats. However, the precise site of octopamine modulation within the cardiac system is not yet known (Kurumoto and Ebara, 1991). One possible site of action is the cardiac ganglion (CG), the CPG in decapod hearts. The transcripts for the enzymes required to synthesize octopamine from tyramine have been identified and localized in the CG (Christie et al., 2018). This would suggest that octopamine is produced in the CG, where it could have a direct action on those neurons, or it could be released peripherally. We have found individual variation in the response to octopamine and its precursor tyramine, and significant effects of frequency and contraction amplitude in the whole heart.

Date: 2006-07-21

Creator: Anna Selmecki, Anja Forche, Judith Berman

Access: Open access

Resistance to the limited number of available antifungal drugs is a serious problem in the treatment of Candida albicans. We found that aneuploidy in general and a specific segmental aneuploidy, consisting of an isochromosome composed of the two left arms of chromosome 5, were associated with azole resistance. The isochromosome forms around a single centromere flanked by an inverted repeat and was found as an independent chromosome or fused at the telomere to a full-length homolog of chromosome 5. Increases and decreases in drug resistance were strongly associated with gain and loss of this isochromosome, which bears genes expressing the enzyme in the ergosterol pathway targeted by azole drugs, efflux pumps, and a transcription factor that positively regulates a subset of efflux pump genes.

Date: 2019-01-01

Creator: Caroline Rice

Access: Open access

Previous studies show that active exploration of an environment contributes to spatial learning more than passive visual exposure (Chrastil & Warren, 2013; Chrastil & Warren, 2015). Active navigation and cognitive decision-making in a novel environment leads to increased spatial knowledge and memory of location compared to a passive exploration that removes the decision-making component. There is evidence of theta oscillations present in electroencephalography (EEG) recordings from the hippocampus and pre-frontal cortex (PFC). These low-frequency waves could reflect spatial navigation and memory performance, suggested by their involvement in communication between the formerly named brain regions. Through communication with the hippocampus, theta oscillations could be involved in the integration of new spatial information into memory. While undergoing EEG, subjects in this study either actively or passively explored a virtual maze, identified as the “Free” or “Guided” groups, respectively. After exploring, subjects’ spatial memory of the maze was tested through a task that required navigation from a starting object to a target object. Behavioral data show increased spatial memory for the Free group, indicated by significantly greater navigation to the correct target object in the memory task. EEG results indicate significantly greater theta oscillations in frontal regions for the Free group during the exploration phase. These results support those found in previous studies and could indicate a correlation between frontal theta oscillations during learning of novel environments and spatial memory.

• Restriction End Date: 2025-06-01

Date: 2022-01-01

Creator: Abigail Raymond

Access: Access restricted to the Bowdoin Community

• Embargo End Date: 2025-05-19

Date: 2022-01-01

Creator: Alissa Chen

Access: Embargoed

Date: 2020-01-01

Creator: Emily R Oleisky

Access: Access restricted to the Bowdoin Community

Date: 2012-02-01

Creator: Erika Nyhus, Tim Curran

Access: Open access

Dual process models suggest that recognition memory is supported by familiarity and recollection processes. Previous research administering amnesic drugs and measuring ERPs during recognition memory have provided evidence for separable neural correlates of familiarity and recollection. This study examined the effect of midazolam-induced amnesia on memory for details and the proposed ERP correlates of recognition. Midazolam or saline was administered while subjects studied oriented pictures of common objects. ERPs were recorded during a recognition test 1 day later. Subjects' discrimination of old and new pictures as well as orientation discrimination was worse when they were given midazolam instead of saline. As predicted, the parietal old/new effect was decreased with the administration of midazolam. However, weaker effects on FN400 old/new effects were also observed. These results provide converging pharmacological and electrophysiological evidence that midazolam primarily affects recollection as indexed by parietal ERP old/new effects and memory for orientation, while also exerting some weaker effects on familiarity as indexed by FN400 old/new effects. © 2011 Massachusetts Institute of Technology.

Date: 2010-09-21

Creator: Hannah R. Snyder, Natalie Hutchison, Erika Nyhus, Tim Curran, Marie T., Banich, Randall C. O'Reilly, Yuko Munakata

Access: Open access

Whether grocery shopping or choosing words to express a thought, selecting between options can be challenging, especially for people with anxiety. We investigate the neural mechanisms supporting selection during language processing and its breakdown in anxiety. Our neural network simulations demonstrate a critical role for competitive, inhibitory dynamics supported by GABAergic interneurons. As predicted by our model, we find that anxiety (associated with reduced neural inhibition) impairs selection among options and associated prefrontal cortical activity, even in a simple, nonaffective verb-generation task, and the GABA agonist midazolam (which increases neural inhibition) improves selection, whereas retrieval from semantic memory is unaffected when selection demands are low. Neural inhibition is key to choosing our words.

Date: 2022-11-15

Creator: Elizabeth R. Chrastil, Caroline Rice, Mathias Goncalves, Kylie N. Moore, Syanah C. Wynn, Chantal E. Stern, Erika Nyhus

Access: Open access

Active navigation seems to yield better spatial knowledge than passive navigation, but it is unclear how active decision-making influences learning and memory. Here, we examined the contributions of theta oscillations to memory-related exploration while testing theories about how they contribute to active learning. Using electroencephalography (EEG), we tested individuals on a maze-learning task in which they made discrete decisions about where to explore at each choice point in the maze. Half the participants were free to make active decisions at each choice point, and the other half passively explored by selecting a marked choice (matched to active exploration) at each intersection. Critically, all decisions were made when stationary, decoupling the active decision-making process from movement and speed factors, which is another prominent potential role for theta oscillations. Participants were then tested on their knowledge of the maze by traveling from object A to object B within the maze. Results show an advantage for active decision-making during learning and indicate that the active group had greater theta power during choice points in exploration, particularly in midfrontal channels. These findings demonstrate that active exploration is associated with theta oscillations during human spatial navigation, and that these oscillations are not exclusively related to movement or speed. Results demonstrating increased theta oscillations in prefrontal regions suggest communication with the hippocampus and integration of new information into memory. We also found evidence for alpha oscillations during active navigation, suggesting a role for attention as well. This study finds support for a general mnemonic role for theta oscillations during navigational learning. © 2022

Date: 2014-01-01

Creator: Anja Forche

Access: Open access

Pathogenic fungi encounter many different host environments to which they must adapt rapidly to ensure growth and survival. They also must be able to cope with alterations in established niches during long-term persistence in the host. Many eukaryotic pathogens have evolved a highly plastic genome, and large-scale chromosomal changes including aneuploidy, and loss of heterozygosity (LOH) can arise under various in vitro and in vivo stresses. Both aneuploidy and LOH can arise quickly during a single cell cycle, and it is hypothesized that they provide a rapid, albeit imprecise, solution to adaptation to stress until better and more refined solutions can be acquired by the organism. While LOH, with the extreme case of haploidization in Candida albicans, can purge the genome from recessive lethal alleles and/or generate recombinant progeny with increased fitness, aneuploidy, in the absence or rarity of meiosis, can serve as a non-Mendelian mechanism for generating genomic variation. © Springer Science+Business Media 2014.

Date: 2020-05-01

Creator: Erika Nyhus, William A. Engel, Tomas Donatelli Pitfield, Isabella M.W. Vakkur

Access: Open access

Although there has been recent interest in how mindfulness meditation can affect episodic memory as well as brain structure and function, no study has examined the behavioral and neural effects of mindfulness meditation on episodic memory. Here we present a protocol that combines mindfulness meditation training, an episodic memory task, and EEG to examine how mindfulness meditation changes behavioral performance and the neural correlates of episodic memory. Subjects in a mindfulness meditation experimental group were compared to a waitlist control group. Subjects in the mindfulness meditation experimental group spent four weeks training and practicing mindfulness meditation. Mindfulness was measured before and after training using the Five Facet Mindfulness Questionnaire (FFMQ). Episodic memory was measured before and after training using a source recognition task. During the retrieval phase of the source recognition task, EEG was recorded. The results showed that mindfulness, source recognition behavioral performance, and EEG theta power in right frontal and left parietal channels increased following mindfulness meditation training. In addition, increases in mindfulness correlated with increases in theta power in right frontal channels. Therefore, results obtained from combining mindfulness meditation training, an episodic memory task, and EEG reveal the behavioral and neural effects of mindfulness meditation on episodic memory.

Date: 2019-09-04

Creator: Erika Nyhus, William Andrew Engel, Tomas Donatelli Pitfield, Isabella Marie Wang Vakkur

Access: Open access

Mindfulness meditation has been shown to improve episodic memory and increase theta oscillations which are known to play a role in episodic memory retrieval. The present study examined the effect of mindfulness meditation on episodic memory retrieval and theta oscillations. Using a longitudinal design, subjects in the mindfulness meditation experimental group who underwent 4 weeks of mindfulness meditation training and practice were compared to a waitlist control group. During the pre-training and post-training experimental sessions, subjects completed the Five Facet Mindfulness Questionnaire (FFMQ) and studied adjectives and either imagined a scene (Place Task) or judged its pleasantness (Pleasant Task). During the recognition test, subjects decided which task was performed with each word (“Old Place Task” or “Old Pleasant Task”) or “New.” FFMQ scores and source discrimination were greater post-training than pre-training in the mindfulness meditation experimental group. Electroencephalography (EEG) results revealed that for the mindfulness meditation experimental group theta power was greater post-training than pre-training in right frontal and left parietal channels and changes in FFMQ scores correlated with changes in theta oscillations in right frontal channels (n = 20). The present results suggest that mindfulness meditation increases source memory retrieval and theta oscillations in a fronto-parietal network.

Date: 2004-06-01

Creator: Anja Forche, P. T. Magee, B. B. Magee, Georgiana May

Access: Open access

Single-nucleotide polymorphisms (SNPs) are essential tools for studying a variety of organismal properties and processes, such as recombination, chromosomal dynamics, and genome rearrangement. This paper describes the development of a genome-wide SNP map for Candida albicans to study mitotic recombination and chromosome loss. C. albicans is a diploid yeast which propagates primarily by clonal mitotic division. It is the leading fungal pathogen that causes infections in humans, ranging from mild superficial lesions in healthy individuals to severe, life-threatening diseases in patients with suppressed immune systems. The SNP map contains 150 marker sequences comprising 561 SNPs and 9 insertions-deletions. Of the 561 SNPs, 437 were transition events while 126 were transversion events, yielding a transition-to-transversion ratio of 3:1, as expected for a neutral accumulation of mutations. The average SNP frequency for our data set was 1 SNP per 83 bp. The map has one marker placed every 111 kb, on average, across the 16-Mb genome. For marker sequences located partially or completely within coding regions, most contained one or more nonsynonymous substitutions. Using the SNP markers, we identified a loss of heterozygosity over large chromosomal fragments in strains of C. albicans that are frequently used for gene manipulation experiments. The SNP map will be useful for understanding the role of heterozygosity and genome rearrangement in the response of C. albicans to host environments.

Date: 2008-05-01

Creator: Anja Forche, Kevin Alby, Dana Schaefer, Alexander D. Johnson, Judith, Berman, Richard J. Bennett

Access: Open access

Candida albicans has an elaborate, yet efficient, mating system that promotes conjugation between diploid a and α strains. The product of mating is a tetraploid a/α cell that must undergo a reductional division to return to the diploid state. Despite the presence of several "meiosis-specific" genes in the C. albicans genome, a meiotic program has not been observed. Instead, tetraploid products of mating can be induced to undergo efficient, random chromosome loss, often producing strains that are diploid, or close to diploid, in ploidy. Using SNP and comparative genome hybridization arrays we have now analyzed the genotypes of products from the C. albicans parasexual cycle. We show that the parasexual cycle generates progeny strains with shuffled combinations of the eight C. albicans chromosomes. In addition, several isolates had undergone extensive genetic recombination between homologous chromosomes, including multiple gene conversion events. Progeny strains exhibited altered colony morphologies on laboratory media, demonstrating that the parasexual cycle generates phenotypic variants of C. albicans. In several fungi, including Saccharomyces cerevisiae and Schizosaccharomyces pombe, the conserved Spo11 protein is integral to meiotic recombination, where it is required for the formation of DNA double-strand breaks. We show that deletion of SPO11 prevented genetic recombination between homologous chromosomes during the C. albicans parasexual cycle. These findings suggest that at least one meiosis-specific gene has been re-programmed to mediate genetic recombination during the alternative parasexual life cycle of C. albicans. We discuss, in light of the long association of C. albicans with warm-blooded animals, the potential advantages of a parasexual cycle over a conventional sexual cycle. © 2008 Forche et al.

Date: 2008-03-28

Creator: Francisco Barceló, José A. Periáñez, Erika Nyhus

Access: Open access

This study aimed to clarify the neural substrates of behavioral switch and restart costs in intermittently instructed task-switching paradigms. Event-related potentials (ERPs) were recorded while participants were intermittently cued to switch or repeat their categorization rule (Switch task), or else they performed two perceptually identical control conditions (NoGo and Oddball). The three tasks involved different task-sets with distinct stimulus-response associations in each, but identical visual stimulation, consisting of frequent colored shapes (p = 0.9) and randomly interspersed infrequent black shapes (p = 0.1; '+' and 'x' symbols). Behavioral restart costs were observed in the first target responses following all black shapes in the Switch and NoGo tasks - but not in the Oddball task - and corresponded with enhanced fronto-centrally distributed early cue-locked P3 activity (peak latency 325-375 ms post-cue onset at the vertex). In turn, behavioral switch costs were associated with larger late cue-locked P3 amplitudes in the Switch task only (peak latency 400-450 ms post-cue onset at mid-parietal sites). Together with our information theoretical estimations, ERP results suggested that restart and switch costs indexed two neural mechanisms related to the preparatory resolution of uncertainty: (1) the intermittent re-activation of task-set information, and (2) the updating of stimulus-response mappings within an active task set, as indexed by early and late cue-locked P3 activations, respectively. In contrast, target-locked P3 activations reflected a functionally distinct mechanism related to the implementation of task-set information. We conclude that task-switching costs consist of both switch-specific and switch-unspecific processes during the preparation and execution stages of task performance. © 2008 Barceló, Periáñez and Nyhus.

• Restriction End Date: 2025-06-01

Date: 2022-01-01

Creator: Warsameh Bulhan

Access: Access restricted to the Bowdoin Community

Date: 2023-01-01

Creator: Kenneth Garcia

Access: Open access

Neuromodulation allows for the flexibility of neural circuit dynamics and the outputs they produce. Studies of the stomatogastric nervous system (STNS) have expanded our knowledge on the actions of neuromodulators, small molecules that most often activate G-protein coupled receptors and reconfigure circuit activity and composition. In these systems, modulation has been found to occur at every level, from sensory-motor coupling to neuromuscular transmission (Harris-Warrick and Marder 1991). Neuromodulators have complex effects on motor output; they can alter the firing of individual neurons while also modulating muscle properties, neuromuscular transmission, and sensory neuron response to muscle activity (Fort et al. 2004). We investigated this further by recording the motor output produced by the gastric mill rhythm of the lobster STNS under neuromodulator conditions. How is this neuromuscular system as a whole modulated to produce motor flexibility? We hypothesized that these neuromodulators act on individual receptors of component neurons of central pattern generator (CPG)-effector system themselves and at the periphery, coordinately altering muscle contraction by altering all levels of the crustacean neuromuscular system. Application of NRNFLRFamide, RPCH, oxotremorine, and proctolin to the gastric mill 4 (gm4) muscles of the Cancer crab showed that neuromodulators that have been found to have variable, yet significant effects on the activity of the neurons of the STNS directly alter the activity of the gm4 muscles as well, suggesting that coordination of peripheral actions and direct neuronal modulation regulates patterned motor output.

• Restriction End Date: 2028-06-01

Date: 2023-01-01

Creator: Jada Scotland

Access: Access restricted to the Bowdoin Community

Date: 2023-01-01

Creator: Rowland Luo

Access: Open access

The study of neuronal development could provide foundational information on neurogenesis and neuroplasticity. The small size and relatively simple nervous system of Orthoptera make them ideal models for neurodevelopmental studies. The peripheral nervous system development is an intricate and precise process that each sensory neurons are able to reach their central nervous system partners in a relatively short amount of time. Although the peripheral nervous system in limb buds and their genetic regulations are well understood in grasshopper embryos, few studies have explored the developing nervous system in a cricket model. Therefore, the first goal of the current experiment is to characterize the normal peripheral nervous system development in cricket embryos. Previous studies in Drosophila have suggested Toll6 and Toll7 receptors could serve as important targets for the neurotrophic-like factors Spaetzle2 and 5. Malfunctioning neurotrophic pathways could lead to abnormal nervous system development. Therefore, the second goal of the current study is to explore the roles of Toll7 in the development of the cricket peripheral nervous system. Immunohistochemical staining using anti-horseradish peroxidase (Anti-HRP) was used to illustrate crickets' embryonic developing peripheral nervous system in the limb buds from developmental stage 7.0 to 11.0. Cricket eggs were injected with Toll7 double stranded RNA (dsRNA) and rhodamine dye to suppress the Toll7 mRNA level. The control eggs were injected with GFP dsRNA and rhodamine dye. The peripheral nervous system development in cricket embryos is largely homologous to that observed in grasshopper embryos. All later-emerged sensory neurons followed the pathway established by the first pioneer neuron Ti1. Ti1 made stereotypical turns following the steering signals on epithelial and guidepost cell surfaces and eventually fasciculate with lateral motor axons from the central nervous system. When examining the peripheral nervous system development with Toll7 knockdown, a decrease in limb bud volume was observed at stage 7.7 and stage 8.0, suggesting Toll7’s potential roles in aiding cell-cell intercalation processes in Orthoptera embryos. Furthermore, a delay in Ti1 pioneer neuron development was observed with Toll7 knockdown at early developmental stages, providing evidence for Toll-Spaetzle pathway’s neurotrophic-like functions. The results of the current experiment provide the first description of the peripheral nervous system development in the cricket limb buds and further evidence of Toll-Spaetzle pathway’s neurotrophic properties.

Date: 2025-01-01

Creator: Margaret Broaddus

Access: Open access

ABSTRACT CHAPTER I: All nervous systems are influenced by circulating hormones, which can modulate neural circuits to produce different outputs from the same set of neurons. Invertebrate models, particularly crustaceans, serve as excellent models for studying neuromodulation because they contain neural circuits that continue to generate fictive activity when dissected out of the animal. The stomatogastric nervous system (STNS) of the Jonah Crab (Cancer borealis) has long been used to study neuromodulation due to its well-characterized circuits. Even in such a compact neural network, little is known about how these circuits are modulated, and this remains a question in all animals, particularly in humans. Here we investigated the modulation of the pyloric circuit by applying bulk hemolymph to the dissected STNS preparation. The hemolymph contains all of the circulating modulators, some of which have known effects on the pyloric rhythm (though many are still unknown). Interestingly, when hemolymph is applied to the isolated STNS, the pyloric rhythm is suppressed. This is surprising given that in vivo the STNS is continually exposed to hemolymph (the STG is situated within an artery, and thus, exposed to circulating hemolymph) and the pyloric rhythm is constitutively active. Therefore, I hypothesized that there are synaptically released neurotransmitters that excite the pyloric rhythm. To test this hypothesis, we applied three different excitatory modulators – proctolin, serotonin, and oxotremorine – separately in the presence of hemolymph. I found that proctolin and oxotremorine restore the pyloric rhythm in the presence of hemolymph. However, serotonin did not consistently overcome the inhibition of hemolymph. ABSTRACT CHAPTER II: A plethora of work has begun to identify how endogenous neural and hormonal modulators interact to influence the pyloric network. Here we examined the modulation of the stomatogastric nervous system (STNS) via two excitatory endogenous modulators CabTRP Ia and corazonin. CabTRP Ia and corazonin both excite the pyloric rhythm, but in distinct ways. Preliminary data by Nusbaum and Christie from 2003 suggested that an initial corazonin application gated a stronger response to subsequent CabTRP Ia when compared the inverse application of these neuromodulators. We sought to validate this gating phenomenon, but found no significant difference between the effects of the first and second applications of CabTRP Ia. Given that these animals are wild caught and surviving in a changing oceanic environment, it is possible that this modulatory effect in the Jonah Crab has changed over the last few decades due to environmentally driven shifts in receptor expression and channel conductances.

Date: 2025-01-01

Creator: Aeri Ko

Access: Access restricted to the Bowdoin Community

Date: 2014-12-01

Creator: Anja Wartenberg, Jörg Linde, Ronny Martin, Maria Schreiner, Fabian, Horn, Ilse D. Jacobsen, Sabrina Jenull, Thomas Wolf, Karl Kuchler, Reinhard Guthke, Oliver Kurzai, Anja Forche, Christophe d'Enfert, Sascha Brunke, Bernhard Hube

Access: Open access

Following antifungal treatment, Candida albicans, and other human pathogenic fungi can undergo microevolution, which leads to the emergence of drug resistance. However, the capacity for microevolutionary adaptation of fungi goes beyond the development of resistance against antifungals. Here we used an experimental microevolution approach to show that one of the central pathogenicity mechanisms of C. albicans, the yeast-to-hyphae transition, can be subject to experimental evolution. The C. albicans cph1Δ/efg1Δ mutant is nonfilamentous, as central signaling pathways linking environmental cues to hyphal formation are disrupted. We subjected this mutant to constant selection pressure in the hostile environment of the macrophage phagosome. In a comparatively short time-frame, the mutant evolved the ability to escape macrophages by filamentation. In addition, the evolved mutant exhibited hyper-virulence in a murine infection model and an altered cell wall composition compared to the cph1Δ/efg1Δ strain. Moreover, the transcriptional regulation of hyphae-associated, and other pathogenicity-related genes became re-responsive to environmental cues in the evolved strain. We went on to identify the causative missense mutation via whole genome- and transcriptome-sequencing: a single nucleotide exchange took place within SSN3 that encodes a component of the Cdk8 module of the Mediator complex, which links transcription factors with the general transcription machinery. This mutation was responsible for the reconnection of the hyphal growth program with environmental signals in the evolved strain and was sufficient to bypass Efg1/Cph1-dependent filamentation. These data demonstrate that even central transcriptional networks can be remodeled very quickly under appropriate selection pressure.

• Restriction End Date: 2025-06-01

Date: 2020-01-01

Creator: Rhianna J Patel

Access: Access restricted to the Bowdoin Community

Date: 2024-01-01

Creator: Karin van Hassel

Access: Open access

The cardiac ganglion (CG) is a central pattern generator, a neural network that, when activated, produces patterned motor outputs such as breathing and walking. The CG induces the heart contractions of the American lobster, Homarus americanus, making the lobster heart neurogenic. In the American lobster, the CG is made up of nine neurons: four premotor pacemaker neurons that send signals to five motor neurons, causing bursts of action potentials from the motor neurons. These bursts cause cardiac muscle contractions that vary in strength based on the burst duration, frequency, and pattern. The activity of the CG is modulated by feedback pathways and neuromodulators, allowing for flexibility in the CG’s motor output and appropriate responses to changes in the animal’s environment. Two feedback pathways modulate the CG motor output, the excitatory cardiac muscle stretch and inhibitory nitric oxide feedback pathways. Despite our knowledge of the modulation of the CG by feedback pathways and neuromodulators separately, little is known about how neuromodulators influence the sensory feedback response to cardiac muscle stretch. I found one neuromodulator to modulate each phase of the stretch response differently, one neuromodulator to generally not affect the stretch response, and three neuromodulators to suppress the stretch response. These results suggest neuromodulators can act to produce flexibility in a CPG’s motor output, allowing the system to respond appropriately to changes in an organism’s environment, and allow for variation in CPG responses to different stimuli.

Date: 2023-01-01

Creator: Jackie Seddon

Access: Open access

Neuromodulation, the process of altering the electrical outputs of a neuron or neural circuit, allows an organism to control its physiological processes to meet the needs of both its internal and external environments. Previous work shows that the pyloric pattern of the kelp crab (Pugettia producta) stomatogastric nervous system (STNS) neurons responded to fewer neuromodulators than the Jonah crab (Cancer borealis). Since the kelp crab diet primarily eats kelp, it is possible that the movements of the foregut that control digestion may require less flexibility in functional output compared to an opportunistic feeder. To determine whether a reduced flexibility is correlated with diet, this study compared the modulatory responses in Pugettia to two other species of majoid crabs: Chionoecetes opilio and Libinia emarginata, which are both opportunistic feeders. Pooled data for this study found that Libinia and Chionoecetes responded to all twelve modulators tested. When considering the effect of modulators on stomatogastric ganglion (STG) motor outputs, we must consider whether these modulators also alter the excitatory junction potentials (EJPs) at the neuromuscular junction (NMJ), and whether there are differences in responses across species. To test this, the dorsal gastric nerve (dgn) was stimulated while recording intracellularly from the muscle fibers of the associated gm4 muscles. The NMJ of the gm4 in Cancer borealis did not appear to be broadly modulated, as only RPCH and CabTRP showed increases in amplitude, and RPCH decreased facilitation at 5 Hz.

• Embargo End Date: 2026-05-18

Date: 2023-01-01

Creator: Violet Louise Rizzieri

Access: Embargoed

Date: 2024-01-01

Creator: Nuanxi (Sissi) Feng

Access: Access restricted to the Bowdoin Community

Date: 2016-05-01

Creator: Tess Lameyer

Access: Access restricted to the Bowdoin Community

Date: 2025-01-01

Creator: Emma F.B. Gibbens

Access: Access restricted to the Bowdoin Community

Date: 2022-04-01

Creator: Syanah C. Wynn, Erika Nyhus

Access: Open access

The primary aim of this review is to examine the brain activity patterns that are related to subjectively perceived memory confidence. We focus on the main brain regions involved in episodic memory: the medial temporal lobe (MTL), prefrontal cortex (PFC), and posterior parietal cortex (PPC), and relate activity in their subregions to memory confidence. How this brain activity in both the encoding and retrieval phase is related to (subsequent) memory confidence ratings will be discussed. Specifically, encoding related activity in MTL regions and ventrolateral PFC mainly shows a positive linear increase with subsequent memory confidence, while dorsolateral and ventromedial PFC activity show mixed patterns. In addition, encoding-related PPC activity seems to only have indirect effects on memory confidence ratings. Activity during retrieval in both the hippocampus and parahippocampal cortex increases with memory confidence, especially during high-confident recognition. Retrieval-related activity in the PFC and PPC show mixed relationships with memory confidence, likely related to post-retrieval monitoring and attentional processes, respectively. In this review, these MTL, PFC, and PPC activity patterns are examined in detail and related to their functional roles in memory processes. This insight into brain activity that underlies memory confidence is important for our understanding of brain–behaviour relations and memory-guided decision making. © 2022 The Authors. European Journal of Neuroscience published by Federation of European Neuroscience Societies and John Wiley & Sons Ltd.

Date: 2009-11-01

Creator: Anja Forche, Musetta Steinbach, Judith Berman

Access: Open access

Candida albicans is the most prevalent opportunistic fungal pathogen in the clinical setting, causing a wide spectrum of diseases ranging from superficial mucosal lesions to life-threatening deep-tissue infections. Recent studies provide strong evidence that C. albicans possesses an arsenal of genetic mechanisms promoting genome plasticity and that it uses these mechanisms under conditions of nutritional or antifungal drug stress. Two microarray-based methods, single nucleotide polymorphism (SNP) and comparative genome hybridization arrays, have been developed to study genome changes in C. albicans. However, array technologies can be relatively expensive and are not available to every laboratory. In addition, they often generate more data than needed to analyze specific genomic loci or regions. Here, we have developed a set of SNP-restriction fragment length polymorphism (RFLP) (or PCR-RFLP) markers, two per chromosome arm, for C. albicans. These markers can be used to rapidly and accurately detect large-scale changes in the C. albicans genome including loss of heterozygosity (LOH) at single loci, across chromosome arms or across whole chromosomes. Furthermore, skewed SNP-RFLP allelic ratios are indicative of trisomy at heterozygous loci. While less comprehensive than array-based approaches, we propose SNP-RFLP as an inexpensive, rapid, and reliable method to screen strains of interest for possible genome changes. © 2009 Federation of European Microbiological Societies.

Date: 2016-02-11

Creator: Meleah A. Hickman, Guisheng Zeng, Anja Forche, Matthew P. Hirakawa, Darren, Abbey, Benjamin D. Harrison, Yan Ming Wang, Ching Hua Su, Richard J. Bennett, Yue Wang, Judith Berman

Access: Open access

Date: 2017-07-01

Creator: Robert T. Todd, Anja Forche, Anna Selmecki

Access: Open access

The ability of an organism to replicate and segregate its genome with high fidelity is vital to its survival and for the production of future generations. Errors in either of these steps (replication or segregation) can lead to a change in ploidy or chromosome number. While these drastic genome changes can be detrimental to the organism, resulting in decreased fitness, they can also provide increased fitness during periods of stress. A change in ploidy or chromosome number can fundamentally change how a cell senses and responds to its environment. Here, we discuss current ideas in fungal biology that illuminate how eukaryotic genome size variation can impact the organism at a cellular and evolutionary level. One of the most fascinating observations from the past 2 decades of research is that some fungi have evolved the ability to tolerate large genome size changes and generate vast genomic heterogeneity without undergoing canonical meiosis.

Date: 2021-01-01

Creator: Andrew Moore

Access: Access restricted to the Bowdoin Community

Date: 2023-01-01

Creator: Sydney M Bonauto

Access: Access restricted to the Bowdoin Community

• Restriction End Date: 2027-06-01

Date: 2022-01-01

Creator: Patrick F. Bloniasz

Access: Access restricted to the Bowdoin Community

Date: 2016-05-01

Creator: William Andrew Engel

Access: Access restricted to the Bowdoin Community

Date: 2023-01-01

Creator: Elise Martin

Access: Open access

This project sought to answer the following question: what is the relationship between the extent of neuromodulation in a nervous system, and the behavioral demands on that system? A well-characterized CPG neuronal circuit in decapod crustaceans, the stomatogastric nervous system (STNS), was used as a model circuit to answer this question. The stomatogastric ganglion (STG) in the STNS is responsible for muscular contractions in the stomach that aid in digestion. It has been shown that the neural networks in the STG are subject to neuromodulation. One feature of neuromodulation is that it enables circuit flexibility, which confers upon a system the ability to produce variable outputs in response to specific physiological demands. It was hypothesized that opportunistic feeders require more extensively modulated digestive systems compared to exclusive feeders, because opportunistic feeders require a greater variety of digestive outputs to digest their varied diets. In this study, Chionoecetes opilio and Libinia emarginata, the opportunistic feeders, showed greater neuromodulatory capacity of the STNS than Pugettia producta, the exclusive feeder. The hypothesis that neuromodulatory capacity of the STNS correlates with dietary diversity was supported. The results detailed in this study lend credence to the idea that evolutionary basis for neuromodulatory capacity of a system is related to the behavioral demands on that system.

Date: 2023-01-01

Creator: John T Woolley

Access: Open access

Picrotoxin (PTX) has been employed extensively as a tool within the crustacean stomatogastric nervous system (STNS) for its efficacy in blocking K+ and Cl+ currents gated by both GABA and glutamate. Through blocking some currents in the STNS, PTX allows for examination of other components without their presence. However, effects of PTX are relatively unknown within the lobster’s cardiac ganglion (CG). As an incredibly small nervous system of only nine neurons, the lobster CG presents an excellent model system for studying neural circuits. Given that the chemical synapses in the CG are mediated by glutamate, the present study aimed to investigate the action of PTX in the lobster CG with the intent of better understanding its pharmacological impacts as a potential tool for studying the system. Therefore, this study aimed to establish the effects of PTX on CG responses to the application of exogenous GABA or glutamate. When data from both modulators were pooled, PTX applied at a concentration of 10-5M had significant effects on burst duration but not duty cycle or burst frequency of the CG. PTX did suppress GABA (5x10-5M) mediated inhibition of burst duration and duty cycle. PTX did not have any significant effects on burst duration, duty cycle, or frequency compared to exogenous glutamate application. These results indicate that glutamatergic inhibitory synapses are not present in the CG and PTX partially suppresses only GABAergic responses in this system.

Date: 2022-01-01

Creator: Anthony Yanez

Access: Open access

Central pattern generators are neural circuits that can independently produce rhythmic patterns of electrical activity without central or periphery inputs. They control rhythmic behaviors like breathing in humans and cardiac activity in crustaceans. Rhythmic behaviors must be flexible to respond appropriately to a changing environment; this flexibility is achieved through the action of neuromodulators. The cardiac ganglion of Homarus americanus, the American lobster, is a central pattern generator made up of four premotor neurons and five motor neurons. Membrane currents in each cell type, which can be targeted for modulation by various molecules, generate rhythmic bursts of action potentials. Myosuppressin, a FMRFamide-like peptide, is one such neuromodulator. The currents targeted for neuromodulation by myosuppressin are unknown. I investigated the molecular and physiological underpinnings of the modulatory effect of myosuppressin on motor neurons in the cardiac ganglion. First, using single cell RT-qPCR, I determined that across animals, motor neurons express myosuppressin receptor subtype II at equal levels relative to each other. Using sharp intracellular recordings, I showed that myosuppressin decreased burst frequency and the rate of depolarization during the inter-burst interval. I predicted that this effect resulted from the modulation of either A-type potassium current or calcium-dependent potassium current. Using two-electrode voltage clamp, I found that total outward current did not substantially change after treatment with myosuppressin. This result was surprising and provides grounds for explorations of subtle forms of neuromodulation in simple neural circuits.

• Embargo End Date: 2027-05-16

Date: 2024-01-01

Creator: Connor Joseph Latona

Access: Embargoed

Date: 2018-05-01

Creator: Sara Spicer

Access: Open access

The well-conserved semaphorin family of guidance molecules is known to play multiple complex roles in directing the growth and orientation of dendrites and axons within the developing invertebrate central and peripheral nervous system. Additionally, the expression of select semaphorins is maintained within some highly plastic areas of the adult central nervous system, such as the mushroom bodies, where they are associated with guidance of newly-born neurons as well as with synapse formation and modification. Within the cricket species Gryllus bimaculatus, deafferentation of the prothoracic ganglia and subsequent dendritic rearrangement of the auditory interneurons is associated with fluctuations in the expression of transmembrane Sema1a and diffusible Sema2a. Here, we characterize the expression of two different variants of Gryllus Sema1a, termed Horch Sema1a and Extavour Sema1a, in tissues associated with both developmental neuronal guidance and adult structural plasticity: the embryonic limb buds, the mushroom bodies of the brain, and the non-deafferented adult prothoracic ganglion. Although we were unable to visualize the expression of Extavour Sema1a in any tissue, we demonstrate via phylogenetic analysis that both Sema1a variants have homologs in species across the Insecta class, suggesting that Extavour SEMA1a is a conserved protein sequence. We observe no expression of Horch Sema1a in the embryonic limb bud, and suspect that Extavour Sema1a, which has a high pairwise identity with Schistocerca Sema1a, could be facilitating guidance of the tibial pioneer neuron growth in the limb bud, along with Sema2a. In the adult brain, we observe a colocalization of Horch Sema1a and Sema2a in the mushroom bodies and in a vertical stripe across the calyx, which may be indicative of interactions between Horch SEMA1a and SEMA2a in maintaining synaptic plasticity and guiding newly-born Kenyon cells. We also report a colocalization of Horch Sema1a and Sema2a in the anterior and posterior of the prothoracic ganglia on the ventral side, in the region of auditory interneuron cell bodies, suggesting the possibility that auditory interneurons may express both Horch Sema1a and Sema2a, which could interact with each other or with Plexin receptors to regulate dendrite morphology at the midline.

Date: 2024-01-01

Creator: Josephine P. Tidmore

Access: Open access

Central pattern generator (CPG) networks produce the rhythmic motor patterns that underlie critical behaviors such as breathing, walking, and heartbeat. The fidelity of these neural circuits in response to fluctuations in environmental conditions is essential for organismal survival. The specific ion channel profile of a neuron dictates its electrophysiological phenotype and is under homeostatic control, as channel proteins are constantly turning over in the membrane in response to internal and external stimuli. Neuronal function depends on ion channels and biophysical processes that are sensitive to external variables such as temperature, pH, and salinity. Nonetheless, the nervous system of the American lobster (Homarus americanus) is robust to global perturbations in these variables. The cardiac ganglion (CG), the CPG that controls the rhythmic activation of the heart in the lobster, has been shown to maintain function across a relatively wide, ecologically-relevant range of saline concentrations in the short-term. This study investigates whether individual neurons of the CG sense and compensate for long-term changes in extracellular ion concentration by controlling their ion channel mRNA abundances. To do this, I bathed the isolated CG in either 0.75x, 1.5x, or 1x (physiological) saline concentrations for 24 h. I then dissected out individual CG motor neurons, the pacemaker neurons, and sections of axonal projections and used single-cell RT-qPCR to measure relative mRNA abundances of several species of ion channels in these cells. I found that the CG maintained stable output with 24 h exposure to altered saline concentrations (0.75x and 1.5x), and that this stability may indeed be enabled by changes in mRNA abundances and correlated channel relationships.

Date: 2025-01-01

Creator: Cassidy J. Scott

Access: Access restricted to the Bowdoin Community

Date: 2025-01-01

Creator: Ephraim Kyenkyenhene Boamah

Access: Access restricted to the Bowdoin Community

Date: 2010-07-01

Creator: Anna Selmecki, Anja Forche, Judith Berman

Access: Open access

The genomic plasticity of Candida albicans, a commensal and common opportunistic fungal pathogen, continues to reveal unexpected surprises. Once thought to be asexual, we now know that the organism can generate genetic diversity through several mechanisms, including mating between cells of the opposite or of the same mating type and by a parasexual reduction in chromosome number that can be accompanied by recombination events (2, 12, 14, 53, 77, 115). In addition, dramatic genome changes can appear quite rapidly in mitotic cells propagated in vitro as well as in vivo. The detection of aneuploidy in other fungal pathogens isolated directly from patients (145) and from environmental samples (71) suggests that variations in chromosome organization and copy number are a common mechanism used by pathogenic fungi to rapidly generate diversity in response to stressful growth conditions, including, but not limited to, antifungal drug exposure. Since cancer cells often become polyploid and/or aneuploid, some of the lessons learned from studies of genome plasticity in C. albicans may provide important insights into how these processes occur in higher-eukaryotic cells exposed to stresses such as anticancer drugs. © 2010, American Society for Microbiology.

Date: 2018-02-01

Creator: Erika Nyhus

Access: Open access

Evidence from fMRI has consistently located a widespread network of frontal, parietal, and temporal lobe regions during episodic retrieval. However, the temporal limitations of the fMRI methodology have made it difficult to assess the transient network dynamics by which these distributed regions coordinate activity. Recent evidence suggests that beta oscillations (17-20 Hz) are important for top-down control for memory suppression. However, the spatial limitations of the EEG methodology make it difficult to assess the relationship between these oscillatory signals and the distributed networks identified with fMRI. This study used simultaneous EEG/fMRI to identify networks related to beta oscillations during episodic retrieval. Participants studied adjectives and either imagined a scene (Place Task) or judged its pleasantness (Pleasant Task). During the recognition test, participants decided which task was performed with each word (“Old Place Task” or “Old Pleasant Task”) or “New.” EEG results revealed that posterior beta power was greater for new than old words. fMRI results revealed activity in a frontal, parietal network that was greater for old than new words, consistent with prior studies. Although overall beta power increases correlated with decreased activity within a predominantly parietal network, within the right dorsolateral and ventrolateral pFC, beta power correlated with BOLD activity more under conditions requiring more cognitive control and EEG/fMRI effects in the right frontal cortex correlated with BOLD activity in a frontoparietal network. Therefore, using simultaneous EEG and fMRI, the present results suggest that beta oscillations are related to postretrieval control operations in the right frontal cortex and act within a broader postretrieval control network. © 2017 Massachusetts Institute of Technology.

Date: 2022-06-01

Creator: Syanah C. Wynn, Erika Nyhus, Ole Jensen

Access: Open access

To successfully encode information into long-term memory, we need top-down control to focus our attention on target stimuli. This attentional focus is achieved by the modulation of sensory neuronal excitability through alpha power. Failure to modulate alpha power and to inhibit distracting information has been reported in older adults during attention and working memory tasks. Given that alpha power during encoding can predict subsequent memory performance, aberrant oscillatory modulations might play a role in age-related memory deficits. However, it is unknown whether there are age-related differences in memory performance or alpha modulation when encoding targets with distraction. Here we show that both older and younger adults are able to encode targets paired with distractors and that the level of alpha power modulation during encoding predicted recognition success. Even though older adults showed signs of higher distractibility, this did not harm their episodic memory for target information. Also, we demonstrate that older adults only modulated alpha power during high distraction, both by enhancing target processing and inhibiting distractor processing. These results indicate that both younger and older adults are able to employ the same inhibitory control mechanisms successfully, but that older adults fail to call upon these when distraction is minimal. The findings of this study give us more insight into the mechanisms involved in memory encoding across the lifespan. © 2020 Federation of European Neuroscience Societies and John Wiley & Sons Ltd.

Date: 2019-01-01

Creator: Louis Mendez

Access: Open access

Central pattern generators (CPGs) are neural networks that generate rhythmic motor patterns to allow organisms to perform stereotypical tasks, such as breathing, scratching, flying, and walking. The American lobster, Homarus americanus, is a simple model system whose CPGs are functionally analogous to those in vertebrate models and model complex rhythmic behaviors. CPGs in many Crustacea, including the American lobster, have been studied because of their ability to maintain biological function after isolation in physiologically relevant conditions. The cardiac ganglion (CG) is a CPG consisting of five larger motor neurons and four smaller pacemaker neurons that innervate the cardiac neuromuscular system and generate electrical bursts that drive patterned behaviors. Neuromodulators, such as neuropeptides, are known to modulate neural output in the CPGs of the American lobster. Currently, neuromodulators affecting the cardiac ganglia are thought to be mainly expressed and secreted outside of the cardiac ganglia, acting as extrinsic neuromodulators. However, there is current evidence to support the idea that neuromodulators can be intrinsically expressed within the cardiac ganglion of the American lobster. Preliminary studies using transcriptomic techniques on genomic and transcriptomic information indicate that neuropeptides are likely expressed within the cardiac ganglion. However, little research has been done to determine whether these neuropeptides are expressed in the cardiac ganglion of the American lobster. Therefore, the purpose of this study is to combine bioinformatics and mass spectrometric techniques to determine whether select neuropeptides are present in the cardiac ganglion within the cardiac neuromuscular system of the American lobster, Homarus americanus. Our data mining techniques using protein query sequences obtained from previously annotated brain and eyestalk transcriptomes resulted in the identification of 22 putative neuropeptides preprohormones from 17 neuropeptide families and 20 putative neuropeptide receptors from 17 neuropeptide receptor families in the CG transcriptome. Additionally, 9 putative neuropeptide receptors from 7 neuropeptide receptor families were detected in the cardiac muscle transcriptome. Of the 17 neuropeptide families detected, receptors for 9 of these neuropeptide families were detected in the CG transcriptome. Receptors for 6 of the neuropeptide families were also present in the cardiac muscle transcriptome. Interestingly, receptors for 6 of neuropeptide families detected were not found in either the CG or cardiac muscle transcriptomes, and receptors for 4 neuropeptide families that weren’t detected in the CG transcriptome were found in the cardiac muscle transcriptome. Therefore, our research suggests that neuropeptides are able to modulate CPG activity extrinsically, either though hormonal or local delivery, or intrinsically. Additionally, neuropeptides were extracted from the stomatogastric ganglion and the commissural ganglion using a scaled-down neuropeptide extraction protocol to estimate the number of tissues required to obtain sufficiently strong mass spectrometry signals. Pooled samples with two commissural ganglia and single samples of a commissural ganglion and a stomatogastric ganglion displayed little signal and an increase in larger peptides and impurities relative to single-tissue samples. Therefore, further optimization of the scaled-down neuropeptide extraction protocol must be done prior to analysis of a cardiac ganglion in the American lobster.

Date: 2020-01-01

Creator: Felicia F. Wang

Access: Access restricted to the Bowdoin Community