Thesis Seminars

Daulton Myers - PhD Candidate, Neuroscience Graduate Program

The anterior cingulate cortex (ACC) is a heterogenous structure that is strongly connected with the amygdala and contains subdivisions critical for unique limbic and cognitive functions. The subgenual ACC (sgACC, Brodmann area 25/14c), implicated in major depression in humans, is a key node of the salience network and is important for arousal state modulation and valuation of sensory information. The perigenual ACC (pgACC, Brodmann area 32/24b), which is positioned dorsal to the sgACC, is important for a host of cognitive functions including decision-making and conflict monitoring. Despite known functional differences in sgACC and pgACC, the main cortical and thalamic drivers of the ACC subregions are not fully understood in higher species. Our preliminary data in macaque suggests each region is unique. sgACC is weighted towards prefrontal cortical (PFC) and thalamic afferents carrying information about motivational states and the value of sensory cues, including midline thalamic nuclei and Brodmann area 13. In contrast, pgACC receives unique inputs from mediodorsal (MD) thalamus and Brodmann area 9/46 that carry information important for spatial and temporal localization of salient stimuli. In Aim 1, I will use paired retrograde tracer injections and compare ensembles of prefrontal cortical and thalamic afferents to the macaque sgACC and pgACC within the same animals. I hypothesize that unique combinations of inputs drive sgACC and pgACC, with sgACC being weighted towards key areas of the arousal network and pgACC being weighted towards cortical and thalamic areas important for goal-directed behavior and decision-making.

The amygdala is critical for ACC function, but its specific inputs to sgACC and pgACC are not clear. The basal nucleus of the amygdala, a 'cortical-like' nucleus critical for detection of salient cues such as facial expression and facial identity, has strong inputs to the ACC. The basal nucleus of the amygdala is enlarged in primates compared to rodents and is subdivided into a dorsal magnocellular division (Bmc), a ventral parvicellular division (Bpc), and an intermediate subdivision (Bi). These cellular divisions are based on size and density of glutamatergic pyramidal neurons. Since glutamatergic projection neurons are specialized at the molecular level, it is possible that glutamatergic neurons in the basal nucleus exhibit distinct transcriptional profiles that encode their projection targets. In Aim 2A, I will use long-read single-nucleus RNA sequencing to characterize the transcriptional profiles of glutamatergic neurons in the macaque basal nucleus of the amygdala. I hypothesize that a gradient of excitatory neuron subtype-specific gene expression will be revealed, with unique glutamatergic neuron types present in the Bmc, Bi, and Bpc. In Aim 2B, an atlas of differentially express genes in the basal nucleus subdivisions will be validated with spatial transcriptomics (RNAScope).

While the sgACC and pgACC act as discrete functional and connectional hubs, preliminary data show that they receive a common input from the Bi, which may function to coordinate responses to salient social stimuli. I hypothesize that excitatory Bi neurons projecting to sgACC and pgACC will exhibit distinct transcriptional profiles compared to neurons that do not target the ACC. In Aim 3, information from transcriptomic studies (Aim 2) will be used to determine the molecular features of Bi-ACC projection neurons. Using cases from Aim 1, retrogradely labeled neurons in the basal nucleus of the amygdala projecting to sgACC and pgACC will be double labeled for fluorescent in situ hybridization (RNAScope). These results will then be integrated with the results of Aim 1 for a comprehensive analysis of sgACC and pgACC connectivity. Overall, this will provide insight on how the unique functions of sgACC and pgACC are established and coordinated to guide decision-making in the presence of salient social stimuli, and will be informative for understanding ACC dysregulation in psychiatric disorders.

 Dec 17, 2024 @ 9:00 a.m.

 Medical Center | K307 (3-6408)

Host: Julie Fudge, MD

Matthew Adusei, MS - PhD Candidate, Neuroscience Graduate Program

Visual signals follow a feedforward progression: the dorsal lateral geniculate nucleus (LGN) receives and relays signals from the retina to primary visual cortex (V1). V1, in turn, provides reciprocal feedback to the LGN. Because the vast majority of LGN inputs target V1 (and secondary visual cortex or V2), their complementary corticogeniculate neurons are assumed to be similarly restricted to V1 and V2. However, there are direct inputs mainly from koniocellular LGN neurons to mid-level, extrastriate visual areas. Whether there are corticogeniculate neurons in mid-level extrastriate cortex that project to the LGN remains unknown. Additionally, since corticogeniculate neurons in V1 modulate the timing and precision of LGN responses, it would be important to investigate whether extrastriate corticogeniculate neurons serve analogous or different functions. In this thesis work, I investigate these unknown questions using virus-mediated gene delivery to 1) retrogradely trace corticogeniculate circuits and 2) optogenetically activate corticogeniculate feedback in primates and ferrets, carnivores with visual pathways similar to those in primates.

First, we identified and characterized the morphology of multiple distinct corticogeniculate neurons in mid-level extrastriate visual cortical areas of ferrets: posteromedial lateral suprasylvian (PMLS), posterolateral lateral suprasylvian (PLLS), and area 21a, and macaque monkeys: middle temporal (MT), medial superior temporal (MST), and area V4. Importantly, all three areas in both species were dominated by corticogeniculate neurons with spiny stellate morphology, suggesting possible preferential targeting of W/koniocellular LGN layers. We also observed corticogeniculate neurons in other extrastriate visual cortical areas, although we did not systematically characterize them.

Toward the second aim, we found that activating corticogeniculate feedback from PMLS in ferrets shifted the preferences of LGN neurons to low spatial and high temporal frequency stimuli, which aligns with the preference of PMLS neurons for fast-moving stimuli.

Together, our results suggest that: (1) extrastriate corticogeniculate feedback from PMLS may enhance LGN responses to fast-moving (high temporal frequency) stimuli, (2) evolutionary preservation of corticogeniculate neurons throughout visual cortex supports their critical role in visual function, (3) extrastriate geniculo-cortico-geniculate loops, that bypass V1, could provide a substrate for residual vision following V1 damage, (4) other sensory systems may contain corticothalamic neurons beyond primary and secondary sensory cortex that also target first order thalamus, (5) broader characterizations of these circuits could provide additional clues about the overall functional roles of corticothalamic feedback in sensory perception, and (6) the presence of corticogeniculate neurons across visual cortex necessitates a reevaluation of the LGN as a hub for visual information rather than a simple relay.

Zoom Passcode:  659426

 Nov 22, 2024 @ 9:00 a.m.

 Medical Center | K207 (2-6408)

Host: Advisor: Farran Briggs

Silei Zhu, MS - PhD Candidate, Neuroscience Graduate Program

In the early visual system, functional significance of the feedforward projection, from the retina to the dorsal lateral geniculate nucleus (LGN), and from LGN to the primary visual cortex (V1), is relatively well studied. In contrast, corticogeniculate (CG) feedback to LGN, which mainly originates from V1, is less well understood. Interestingly, CG feedback constitutes more than 30% of total synaptic input onto LGN neurons, outnumbering retinal feedforward synapses (5%-10%). The overall goal of my thesis is to study the behavioral effects of selective manipulation of CG feedback and to develop relevant methods. We first examined the effects of selective optogenetic suppression of CG neurons in anesthetized ferrets. Optogenetic suppression of CG feedback decreased activity among LGN neurons in the absence of visual stimulation but did not affect the visual responses of LGN neurons, suggesting that feedforward visual stimulus drive overrode weak corticogeniculate influence. Optogenetic effects on LGN and V1 neuronal responses depended on the frequency of LED illumination, with higher frequency illumination inducing slow oscillations in V1, dis-inhibiting V1 neurons locally, and producing more suppression among LGN neurons. We then trained ferrets to perform freely moving visual discrimination tasks and tracked their head and eye movements. Heading was predictive of choices as well as biases and decision strategies. While saccades also predicted choices, they were less predictive than heading and occurred after head turning. These findings characterize ferrets' head and eye movements during freely moving visual discrimination tasks and show that when unrestrained, ferrets orient first with their heads and then with their eye movements. Furthermore, these methods also provide a unique paradigm to probe the continuous process of visual decision-making in a more naturalistic manner. We also developed methods of long-term viral expression of genes of interest in ferrets. We injected AAV2 locally in V1 and confirmed viral expression in V1 neurons 14 months post-injection. However, AAV2-retro did not retrogradely label CG neurons after injection into ferret LGN. Instead, FuG-E lentivirus retrogradely infected CG neurons after injection into LGN and we confirmed viral gene expression 9 months post injection. Interestingly, FuG-E lentivirus barely labeled any neurons after local injection in V1. To determine the visual field affected by viral infection, we first mapped the retinotopy of ferret V1 on a ferret MRI brain atlas, and then registered virus expression patterns to this atlas to obtain the elevation and azimuth of each virus-infected neuron. We expressed inhibitory chemogenetic channels in V1 in one ferret but did not detect any behavioral effects of chemogenetic inactivation. To test the behavioral impact of optogenetic activation of CG neurons, we injected FuG-E lentivirus expressing ChR2 into LGN to label CG neurons in V1 retrogradely. After stimulation of CG neurons using wireless optogenetics during freely moving visual discrimination tasks, we detected a significant decrease of task performance in one ferret specifically in the visual field contralateral to the LGN injected with virus. However, at 10 months after the detection of behavioral changes, we did not detect viral expression in post-mortem histology. No significant behavioral effect was found in another animal 4-10 months post-injection, perhaps due to mismatch between the position of the visual stimulus and the retinotopic location of virus-infected neurons. Through these experiments, we learned the importance of completing behavioral tests within 1 year post viral injection to avoid expression decay, and the importance of developing methods to confirm success of viral expression and estimate affected receptive fields in vivo, e.g. using retinal imaging.

 Nov 21, 2024 @ 9:00 a.m.

 Medical Center | K307 (3-6408)

Host: Advisor: Farran Briggs, PhD

Tanique McDonald - PhD Candidate, Neuroscience Graduate Program

Schizophrenia is a chronic neuropsychiatric disorder that causes severe cognitive and functional impairments and is associated with premature mortality. In conjunction with the debilitating hallmark symptoms (i.e., delusions, hallucinations, and disorganized speech), schizophrenia is also associated with a range of visual deficits that alter perception and contribute to delusion formation. Notable visual system changes include retinal atrophy, reduced retinal signaling, altered contrast sensitivity, and reduced surround suppression. Like the overall disorder, the cause of these visual deficits remains unknown. However, an emerging body of literature suggests that elevated levels of the inflammatory cytokine, TNFa, triggers apoptosis of retinal ganglion cells, which is associated with degenerative effects along the feedforward visual pathway. These neuroprogressive effects are consistent with the aforementioned visual deficits commonly observed in patients with schizophrenia. Additionally, prior research has revealed elevated ocular and systemic levels of TNFa in patients with schizophrenia. Despite this, the link between ocular inflammation and visual deficits in schizophrenia remains speculative. The central hypothesis of this proposal is that there are significant positive relationships between higher ocular TNFa concentrations and the visual system changes commonly observed in patients with schizophrenia. Experiments proposed in Aim 1 will quantify ocular TNFa levels in patients and correlate these findings with measurements of retinal structure, visual system processing, and visual perception. Experiments proposed in Aim 2 will use a newly developed Mustela putorius furo (ferret) model to specify mechanistic electrophysiological changes to early components of the visual system (retina, visual thalamus, primary visual cortex) following exacerbation of ocular inflammation via TNFa. The proposed translational study will clarify the cellular and electrophysiologic bases for specific visual system deficits and validate the first animal model of visual anatomical and perceptual impairments in schizophrenia. This work also has potential implications for the development of biomarkers for early detection and monitoring of neuroprogression, and for animal modeling and other research strategies addressing visual system changes associated with neurodegenerative, and psychosis-related disorders.

 Oct 11, 2024 @ 2:00 p.m.

 Medical Center | K207 (2-6408)

Host: Advisors: Farran Briggs, PhD and Steven Silverstein, PhD

Erin Murray - PhD Candidate, Neuroscience Graduate Program

Depression, one of the leading causes of disability worldwide, manifests in various subtypes, including postpartum depression (PPD), which presents after the critical window of pregnancy. Two common, co-occurring environmental factors, exposure to endocrine disrupting chemicals (EDCs) and psychological stress, both disrupt hypothalamic-pituitary-adrenal (HPA) function. Independently, these environmental factors are both associated with increased risk for PPD. Stress can alter neurotransmitter balance and neuroplasticity, trigger neuroinflammation, and produce depressive-like behaviors, such as reduced motivation. Of the many EDCs, perfluorooctanoic acid (PFOA) is found ubiquitously in nearly all pregnant women and infants. Although PFOA and stress both act upon the HPA axis, it remains to be determined whether co-exposure to these factors results in enhanced hormone production or enhanced disruption of the metabolic, immunological, and neurological changes that occur during pregnancy that are related to depressive-like behaviors. Preliminary data from our laboratory has shown that mouse dams exposed to stress and PFOA (100 ng/kg/day - PFOA+S) exhibit unique increases in serum corticosterone and altered metabolic profiles within the frontal cortex (FC), a region found dysregulated in patients with depression that provides critical modulatory feedback to reward-related brain regions. Additionally, our data indicates stress induced increases in activity and self-directed behaviors (grooming and increased localized spontaneous movement). However, effects on motivation, a more translationally relevant behavioral domain for depression, have yet to be evaluated. It is unclear if motivation and stress-induced activity-related behaviors are modulated by the same underlying mechanisms during pregnancy and in the postpartum period. Furthermore, HPA axis activation drives the metabolic support critical for energic homeostasis throughout pregnancy and modulates production of cytokines necessary for immune function and suppression critical to fetal growth and development. Tryptophan metabolism is known to be regulated by both immune and HPA axis, and tryptophan concentrations decrease across gestation in both serum and in brain. Therefore, it is important to understand how the bidirectional regulation between the immune and metabolic systems may be dysregulated in dams exposed to PFOA+S and how this potential dysregulation may affect behavior. To address these questions, we will use a novel resource deprivation paradigm modeling psychosocial stress to examine the combinatorial effects of both gestational stress and low dose PFOA on maternal brain and behavior in C57Bl6/J mice. We aim to 1) test the hypothesis that PFOA plus stress reduces motivation in pregnant dams by developing a behavioral assay of motivation for pup access, 2) identify molecular targets of stress-induced increases in stereotypic behavior and increased self-grooming and motivation, and 3) explore how endocrine activation by PFOA and stress modulates the relationship between tryptophan metabolism and immune markers. In addition to improving upon current rodent models of psychosocial stress in females, which is critical for strengthening the toolset used to study PPD, this project is essential for advancing a cumulative risk framework for “safe” chemical exposure levels in vulnerable populations.

 Sep 27, 2024 @ 9:00 a.m.

 Medical Center | K307 (3-6408)

Host: Advisor: Marissa Sobolewski, PhD

Jeehyun Kim - PhD Candidate, Neuroscience Graduate Program

Parkinson’s disease (PD) is a progressive neurodegenerative disease that significantly impairs both motor and cognitive functions, including working memory, which are often under-recognized and inadequately addressed by treatments, such as deep brain stimulation (DBS). Understanding the effects DBS, such as in the subthalamic nucleus (STN-DBS), on these functions is crucial for optimizing therapeutic interventions and enhancing patient care. While STN-DBS offers motor symptom relief, it has mixed cognitive outcomes, and its differential impact under varying cognitive loads and stimulation states is not well understood. There is a critical need to better understand the neural mechanisms underlying such STN-DBS effects and to develop objective, multi-modal measures to assess these effects more comprehensively. The proposed project aims to develop and utilize multi-modal measures to elucidate the neural mechanisms underlying cognitive and motor functions in PD and their responses to STN-DBS, thereby enhancing our understanding of the mechanisms and clinical effectiveness of STN-DBS. Aim 1 characterizes the multi-modal measures of cognitive (working memory) and motor (upper extremity motor control) functions in patients with PD compared to neurotypical controls using a Mobile Brain-Body Imaging (MoBI) system. Aim 2 investigates the effects of different STN-DBS states (bilateral off, bilateral on, left-on only, right-on only) on these measures in the same individuals. The MoBI system simultaneously records high-density electroencephalogram (EEG), 3D eye/motion-tracking, and cognitive performance during a visuospatial working memory task with varying memory loads and movement incorporated recall responses. Key multi-modal measures include event-related potential (ERP) components, such as Contralateral Delay Activity (CDA), along with cognitive and motor performance measures. The hypothesis is that STN-DBS will differentially impact cognitive and motor functions based on memory loads and stimulation states. Changes in ERPs will represent the underlying neural mechanisms explaining these behavioral outcomes. It is expected that comparing bilateral and unilateral STN-DBS effects will also reveal how different stimulation states impact cognitive and motor functions, considering task-specific, handedness specific, and disease-specific laterality. This project aims to establish comprehensive multi-modal markers for assessing cognitive and motor functions and their modulation by STN-DBS, ultimately contributing to more effective and personalized care for each patient with PD.

 Sep 25, 2024 @ 8:00 a.m.

 Medical Center | 1-9523/35 Northeastern Rm

Host: Advisors: Ed Freedman, PhD & John Foxe, PhD

Sean Lydon - PhD Candidate, Neuroscience PhD degree program

 Aug 23, 2024 @ 1:00 p.m.

 Medical Center | 1-9525 Northeastern Rm

Host: Advisor: Richard Libby, PhD

Luke Shaw - PhD Candidate, Neuroscience PhD degree program

Primates manipulate features of their environment using their forelimbs and dexterous hands, which are commonly guided by visual perception. It is known that in manual interception of moving targets, humans can make rapid adjustments to rapidly compensate for changes in motion. To date, we lack a complete understanding of the neural control of dynamic reaching. This research first characterizes reaching in a new world primate model, the common marmoset (Callithrix jacchus), and further demonstrates methods to inhibit specific components of the reaching neural control circuit during reaching.

To study dynamic reaching in marmosets, we use an ecologically relevant approach with reaching for live moving crickets. Using this paradigm, we estimate visuomotor delay and the time constant to which marmosets predict future target position, confirming that marmosets share several aspects of predictive reaching found in human interception. We further extend this paradigm to include mechanically controlled targets capable of mimicking the motion of a live cricket. Using this apparatus, we validate findings from live cricket reaching experiments with higher trial yields and novel target motion behavior.

In primates, control of vision-guided reaching involves tight coordination of motor planning centers in premotor cortex and vision processing centers in parietal cortex. It is thought that premotor cortex relays motor information back to parietal cortex enabling prediction and also short visuomotor delays. Here, we test and optimize optogenetic tools for the marmoset to manipulate feedback projections from premotor cortex to parietal cortex and their role in prediction. To accomplish this, we utilize an intersectional approach to express light activated ion channels, or opsins, in feedback projections and validate their efficacy in histology and with electrophysiological recordings using optical stimulation. We also test opsins expressed specifically in inhibitory interneurons to enable rapid suppression of premotor or parietal areas. These optogenetic manipulations when coordinated with reaching behavior will enable us to distinguish the contributions of feedback to predictive reaching.

Defense Announcement

 Aug 22, 2024 @ 1:30 p.m.

 Medical Center | 1-9525 Northeastern Rm.

Host: Advisors: Kuan Hong Wang, PhD and Jude Mitchell, PhD

Mariah Marrero - PhD Candidate, Neuroscience Graduate Program

Postoperative delirium (POD) is the most prevalent surgical complication in geriatric patients – with a global incidence rate of 20% and a three-fold likelihood among individuals over the age of 65. POD is strongly associated with neurocognitive decline (NCD), leading to faster rates of cognitive decline with memory deficits. Despite its socioeconomic burden and high incidence rate, the lack of preventative or therapeutic strategies is a pressing issue, largely due to research gaps in molecular signatures of pathology. Clinical evidence shows that increased CSF and High mobility group box 1 (HMGB1) protein plasma are strong predictors for POD and neurocognitive decline. HMGB1 is a DNA chaperone-binding protein localized to the nucleus, and when extracellularly released, binds to toll-like receptor-2/4 (TLR2/TLR4) and receptor for advanced glycation end products (RAGE), becoming immunologically active. Exogenous HMGB1 in the bloodstream has been shown to breach the blood-brain barrier (BBB) and enter the brain, increasing protein levels in areas such as the hippocampus. Previous literature shows that increased exogenous HMGB1 in the hippocampus can bind to RAGE receptors on microglia and increase secretion of complement protein C1q, leading to a feedforward loop of activation and synapse-elimination. This relationship has not been explored with POD. Therefore, I propose to investigate the role of HMGB1 signaling in the BBB and neuroinflammation in the context of sterile surgery, with the potential to advance our understanding significantly and potentially lead to developing new preventative or therapeutic strategies for POD. I hypothesize that exogenous HMGB1 from innate immune cells will inflame and disrupt the BBB, causing soluble HMGB1 to enter the hippocampus and activate microglia. Specifically, HMGB1-induced microglia activation will increase complement secretion of C1q, thereby dysregulating microglia-dependent synaptic elimination. I will use a Transwell system to model the blood murine brain microvascular endothelial cells (BMECs) and pericytes (PCs) to address these unknown mechanisms to simulate vascular changes in response to HMGB1. I will also use a mouse model of orthopedic surgery (rod-fixed tibial fractures) analogous to sterile surgical trauma, where we will collect blood and brain samples over 24 hours using both young (3-month-old) and old (20-month-old) mice to address age-related changes. Preliminary data from our lab found significant increases in plasma HMGB1 1 hour and an increase in HMGB1 expression 24 hours after surgery in young mice versus sham. Using these two models; I will investigate HMGB1 signaling in immune cells, BBB, and microglial activation/C1q activation.

Announcement Flyer

 Aug 22, 2024 @ 12:00 p.m.

 Medical Center | 2-6424 (SMD Large Aud.)

Host: Advisor: Harris Gelbard, PhD

Jingi Yang - PhD Candidate, Neuroscience Graduate Program

The magnocellular and parvocellular pathways are the major parallel information processing streams of the early visual system. Signals relayed by these pathways from the retina to the dorsal lateral geniculate nucleus (dLGN), and then to primary visual cortex (V1) are critical for visual image processing and representation. When any of these pathways are disrupted, loss of vision occurs. The structure and function of each pathway have been well characterized. However, little is known about neurophysiological changes in these pathways following injury, such as in V1 stroke or retinal disease.

Previous work in non-human primate models of glaucoma suggests that there is a greater loss of cytochrome oxidase reactivity in parvocellular compared to magnocellular layers of the dLGN (Crawford et al., 2001, Sasaoka et al., 2008), suggesting stream-specific effects of retinal ganglion cell (RGC) degeneration. Furthermore, previous work in non-human primate models of V1 damage suggests relative preservation of visually responsive magnocellular neurons in the dLGN after long-term V1 damage (Yu et al., 2018), and visual training-induced recovery in occipital cortical stroke patients is more effective with motion stimuli, i.e., stimuli that activate the magnocellular stream. My thesis aimed to understand whether functional plasticity in the early visual pathways following cortical or retinal damage is stream-specific.

We hypothesized that both RGC loss and V1 lesions caused by stroke could differentially affect the magnocellular or parvocellular pathways. In the first study of an animal (ferret) model of RGC loss, I examined the impact of the retinal excitotoxic lesions on the physiological response properties of dLGN neurons. Although the majority of contralesional transient and sustained dLGN neurons lost tuning to contrast, sustained neurons had longer response latencies, greater variability in their responses to visual stimuli, and greater changes in their tuning preferences compared to transient neurons. In the second study of visual training-induced recovery in human stroke patients, I showed that adaptive training with static, drifting, or flickering Gabor patches of progressively lower contrasts improved contrast sensitivity for both orientation and motion discrimination in cortically-blind (vision loss due to V1 stroke) participants; however, normal contrast sensitivity was not recovered in any participant. In summary, this work suggests that: (1) More RGCs in the X (parvocellular-like) stream than those in the Y (magnocellular-like) stream degenerate following kainic acid injections into the eye, (2) sustained (parvocellular-like) neurons in the ferret dLGN appear to be less functionally resistant to degeneration 7 days following retinal lesions compared to transient (magnocellular-like) dLGN neurons, (3) lesion to V1 induces a rapid and severe impairment of contrast sensitivity for orientation and motion direction discrimination in the affected hemifield, (4) adaptive training with stimuli containing higher temporal frequencies, optimal for magnocellular pathway, is not more effective than static stimuli. Together, these findings suggest that post-injury functional plasticity in the early visual pathways depends not only on the parallel streams but also on the location of the injury and the type of the injury.

 Jul 03, 2024 @ 1:00 p.m.

 Medical Center | K-207 (2-6408)

Host: Advisors: Farran Briggs, PhD & Krystel Huxlin, PhD

Gregory Reilly, MS - PhD Candidate, Neuroscience Graduate Program

Biological sex is a fundamental dimension of internal state that can have deep influences on behavior. Understanding the mechanisms behind these influences can provide insight into how shared neural circuits are tuned to produce sex-specific behavioral variation. Biological sex can influence both short-term behaviors and longer, more persistent forms of behavior known as behavioral states. In C. elegans, persistent motor behavior, called locomotor states, is well-studied in hermaphrodites. On a patch of food, hermaphrodites will switch between two states of foraging and feeding, called roaming and dwelling respectively. However, while some work has examined motor states in males, these remain poorly characterized. Previous work from our lab has demonstrated that male locomotion is sex-specific; the sexual state of muscle tissue and the nervous system is essential for sex differences in speed and body posture. Therefore, biological sex may also similarly influence locomotor states. We trained a supervised machine learning Random Forest model to detect three locomotor states: roaming, dwelling, and tail chase. In addition, we used a dimensionality reduction analysis, Linear Discrimination Analysis (LDA), to compare the overall characteristics of these states. Furthermore, to measure the transition probability between states, we used a Markov model. While both males and hermaphrodites share the locomotor states of roaming and dwelling, the characteristics of these differ by sex- the amount of time spent in each state, state durations, and transitions between states (temporal differences), as well as the linear speed, curvature, and other characteristics (feature differences), have sexual dimorphism. To understand how sex tunes these locomotor states, we manipulated the sex determination pathway to sex reverse the nervous system in both males and hermaphrodites. Interestingly, we found that pan-neuronally feminized males had similar locomotor state characteristics to hermaphrodites; both temporal and state feature sex differences were eliminated in the feminized males. Yet, masculinized hermaphrodites were indistinguishable from their wildtype counterparts indicating that either male-specific neurons or other tissue played a role in mediating these sex differences. To uncover the mechanisms that biological sex leverages to achieve this sex-specific variance in locomotor states, various neuromodulator knockout mutants known to affect locomotor states were tested. PDFR-1 emerged as a strong candidate as it removed differences in both temporal and features of locomotor states. Preliminary data suggests that PDFR-1 signaling may regulate the temporal sex differences through daf-7, a TGF-ß signal. daf-7 knockout mutants appear to maintain differences in state features but both spend similar amounts of time roaming and dwelling. Given that PDFR-1 signaling has been implicated as the mechanism that regulates sexual dimorphism in daf-7 expression in the ASJ neuron, these results remain promising. Together, our results provide a mechanistic framework for understanding how sex-specific neuronal tuning influences behavioral states.

 Jun 14, 2024 @ 10:00 a.m.

 Medical Center | SMD Lg. Aud. (2-6424)

Host: Advisor: Doug Portman, PhD

Mark Stoessel, MS - PhD Candidate, Neuroscience Graduate Program

Synaptic plasticity allows the central nervous system to incorporate new sensory experiences and information, and its disruption is associated with many neurological and psychiatric disorders. Much recent work has focused on the contribution of non-neuronal central nervous system cells, especially microglia, to synaptic plasticity. Though classically defined by their immune capacities, microglia are vital to many homeostatic processes, including synaptic plasticity of nascent and adult neuronal networks. Despite the emerging consensus that microglial dynamics are critical to brain function during physiological as well as pathological conditions, it is unclear whether these microglial roles and their underlying mechanisms are universal or differ between brain regions. There is a growing body evidence to suggest microglia exhibit a high degree of regional specialization. Cerebellar microglia in particular exhibit unique transcriptional and epigenetic profiles, and distinct functional properties, such as being morphologically less ramified, and less densely distributed than cortical microglia. As a consequence, cerebellar microglia survey less of the parenchyma than cortical microglia but compensate for this by undergoing frequent somatic translocations under homeostatic conditions, a phenomenon not observed in cortex. Despite such differences, cerebellar microglia maintain common microglial functions. Two pathways of interest to cortical microglial mediated synaptic plasticity are purinergic signaling through the P2Y12 receptor and noradrenergic signaling through the β2 adrenergic receptor (β2-AR), both of which have been shown to be critically involved in microglial roles in synaptic remodeling and rapid chemotaxis to sites of injury.

To address this question of regional heterogeneity in microglial signaling we investigated the roles of P2Y12 and β2-AR in cerebellar microglial with a comparison to the known roles of these signaling pathways in cerebral cortex. We desired to understand the contribution of these pathways to the many aspects of microglial function in the adult brain and therefore characterized cerebellar microglial morphology, surveillance, injury response dynamics, gene expression patterns, and contributions to cerebellar learning and plasticity, while manipulating either microglial purinergic or adrenergic signaling. On the whole, our findings suggest that signaling pathways that are present in both cortical and cerebellar microglia may play differential roles in microglial function depending on brain area.

 Jun 12, 2024 @ 1:00 p.m.

 Medical Center | K-207 (2-6408)

Host: Advisor: Ania Majewska, PhD

MaKenna Cealie - PhD Candidate, Neuroscience Graduate Program

Fetal alcohol spectrum disorders (FASD), caused by prenatal alcohol exposure, are the most common cause of non-heritable, preventable mental disability and have no known cure. Physical, cognitive, and behavioral deficits have been reported in FASD, including impairments related to the cerebellum. To elucidate the mechanisms of FASD, we examined microglia, the immune cells of the central nervous system, as well as Purkinje cells, the sole output of the cerebellar cortex, which are both impacted by developmental ethanol exposure. Microglia are dynamic cells and shape neuronal circuit development and connectivity in the cerebellum. However, how cerebellar microglia dynamics and their interactions with neurons are affected by early life exposure to ethanol is unknown. We explored the impact of a third-trimester equivalent binge-level ethanol exposure on cerebellar microglia and microglia-Purkinje cell interactions in adolescent and young adult mice.

We subcutaneously injected Ai9+/-/C3xcr1G/+/L7cre mice with 5.0 g/kg/day of either ethanol or saline from postnatal (P) days 4-9. Mice were then aged to adolescence (P28) and cranial windows were implanted above the cerebellum to allow for two-photon in vivo imaging in both adolescence and young adulthood (P60). We found that in vivo cerebellar microglia dynamics, microglia morphology, and microglia-Purkinje cell interactions were largely unaffected by developmental ethanol exposure in both adolescence and young adulthood. We also examined if a “second-hit” laser ablation injury in young adulthood would uncover differences, but found no changes in cerebellar microglia injury response between ethanol- and saline-dosed animals. We collected the young adults’ brains for confocal imaging to examine a larger number of microglia and Purkinje cells. Microglia density, morphology, and interactions with Purkinje cells were largely unaltered by developmental ethanol exposure. However, Purkinje cell linear frequency was significantly decreased in ethanol-dosed mice.

Overall, we found that cerebellar microglia in adolescent and young adult mice were largely unaffected by developmental ethanol exposure, but Purkinje cells appeared to be more susceptible to its effects. Our work suggests that microglia may return to homeostasis later in life after an early life insult. This work is important to narrow down the mechanisms leading to FASD so future therapies can be developed.

 May 13, 2024 @ 11:00 a.m.

 Medical Center | Lower Adolph Aud. (1-7619)

Host: Advisor: Ania Majewska, PhD

Cody McKee - PhD Candidate, Neuroscience Graduate Program

Protein Phosphatase 1 (PP1) is a major Serine (Ser)/Threonine (Thr) phosphatase responsible for more than half of all Ser/Thr dephosphorylation events in eukaryotic cells. Three genes encode the three major isoforms of PP1 (α, β, and γ). While PP1α and PP1γ are considered major players in synaptic physiology, the neuronal function of PP1β is unknown. Recently, de novo mutations in PP1β have been linked to intellectual developmental disabilities in children, suggesting a critical role for PP1β in the central nervous system. While correlations between PP1 and various other neurodevelopmental/neurodegenerative diseases have been suggested, a causative role for PP1 in many of these contexts has yet to be established. The current study seeks to investigate the neuronal role of PP1β in vivo, and to uncover potential mechanisms by which PP1β influences neuronal function.

A Thy1-Cre mouse line was used to generate neuron specific PP1β conditional KO (PP1β cKO) mice. These mice exhibit a failure to thrive and typically die by 2-3 postnatal weeks. Hippocampal slice recordings demonstrated increased paired-pulse facilitation, suggesting impaired neurotransmitter release. In agreement with studies suggesting activity influences myelination within specific brain regions, we found significantly lower levels of myelin basic protein in the cortex of PP1β cKO mice. Furthermore, to assess the influence of PP1β on myelin function in a predominately activity-independent context, we measured compound action potentials (CAPs) along the optic nerve. Deficits in CAP recordings suggested impaired optic nerve myelination. However, analysis of the electron micrographs failed to detect a significant difference in myelinated axons. Using immunofluorescence, we then uncovered significantly fewer nodes of Ranvier in PP1β cKO mice that could potentially explain the CAP recordings. This deficit in nodes coincided with an increase in phosphorylation of PP1β-specific substrate, myosin light chain, which localizes to nodes of Ranvier. These data suggest a potential role for PP1β in nodal structure that could influence action potential propagation.

To then study the role of PP1β in adolescent mice, we generated a neuron specific inducible PP1β KO mouse line (iKO). These iKO mice exhibit progressive deterioration of hind limb functionality and premature demise at ~4 weeks post recombination. We then uncovered significant changes in various respiratory parameters suggesting a potential mechanism to explain the premature demise. However, while no morphological changes were observed within neuromuscular junctions in the diaphragm, it is possible that neurotransmitter release at these synapses is abrogated, and this will be investigated in the future.

These data support the hypothesis that PP1β alters action potential propagation in a way that disrupts downstream functionality. These results shed light on the role of PP1β and potential mechanisms that could be disrupted by PP1β in pathological states. Future studies will seek to uncover the molecular substrates underlying these effects and provide potential therapeutic targets for diseases in which PP1β functionality may be altered.

 May 10, 2024 @ 2:00 p.m.

 Medical Center | K-207 (2-6408)

Host: Advisor: Houhui (Hugh) Xia