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The relationship between gut microbiota and host brain health has seen a surge in recent scientific investigation, specifically the causal link between gut imbalance and neuropsychiatric disorders. To increase our understanding of the gut-brain axis, we investigate the molecular interactions of a common bacterial fragment in the gut and its influence in the brain on a cellular level. This study uses primary neural cells in culture as well as an adult rat model to observe the fate of bacteria in the brain and peripheral organs. Cultured neural samples and adult rats were treated with Muramyl dipeptide (MDP), a common bacterial fragment. Relative gene expression was evaluated with rt-PCR across a zero to 24-hr time course post-treatment. Cells and adult rat brain tissues were fixed and stained using immunochemistry to detect the presence and location of the MDP molecule. Using confocal microscopy, we can visualize the time course of interactions between this bacterial fragment and microglia, the innate immune cells of the brain. Early results indicate that microglia will phagocytose these bacterial fragments that travel from the gut to the brain.

Delaware Neuroscience Symposium 2021

Tracking a labeled bacterial cell wall fragment throughout the body and the brain to determine their specific cellular and molecular interactions

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Join the AMA Research Challenge poster symposium and semifinals to explore top research posters and score posters in the semifinals (an AMA member exclusive opportunity).

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This annual event showcases and celebrates the neuroscience research in Delaware.  Posters and talks highlight neuroscience research carried out by graduate students, undergraduate students, and research staff at all of Delaware’s research and education institutions. The Lounge section of the symposium allows real-time interactions and networking among attendees.  New this year is an expo of research core facilities in Delaware.  Check them out in the Research Cores section of our poster session, or see the logos below.

According to the Centers for Disease Control (CDC), about 1 in 9 women experience symptoms of postpartum depression (PPD) after the birth of a child. One focus of research has been to better understand risk factors for PPD. Particularly, the present study aimed to assess the association of various risk factors with postpartum depression severity using a dataset that included variables such as previous mental health status, social factors, societal factors, health care access, as well as other state-wide or region-specific variables. We obtained the most recently available (2016-2017) dataset from the Pregnancy Risk Assessment Monitoring System (PRAMS), which is a dataset compiled by the CDC that collects state-specific, population-based data on maternal attitudes and experiences before, during, and shortly after pregnancy. We utilized a hierarchical linear model to analyze the data across various levels, with a symptom severity scale (0-8) as the dependent variable. Of the 21 variables included in the final model, 9 variables were statistically significant predictors of symptom severity. Statistically significant predictors of postpartum depression symptom severity included previous depression diagnosis and depression symptoms during term, baby residing with mother, unintentional pregnancy, education, Women Infants Children (WIC) enrollment, and marital status. In contrast to these other factors, a postpartum follow up appointment significantly decreased symptom severity. Age revealed an inverted curve in predicting postpartum symptom severity. There was minimal discrepancy of symptom severity scores among the 39 participating states. Postpartum depression symptom severity was associated most notably with previous depression diagnosis and previous symptom severity, but our results also reveal novel social and education factors that contribute to the support and well-being of the mother and child.

Understanding Risk Factors for Postpartum Depression using the PRAMS Dataset

MicroRNA-124 (miR-124) plays a conserved role in regulating parts of neurogenesis; however, its additional function in various developmental processes is less defined. We aim to elucidate the function of miR-124 in early development, using the purple sea urchin (Strongylocentrotus purpuratus) as a model. The sea urchin has one of the most well-documented gene regulatory networks (GRN), making it an excellent model to integrate the regulatory role of miR-124 into its GRN. To identify the function of miR-124, we microinjected miR-124 inhibitor into newly fertilized eggs and examined specific cell type and tissue phenotypes. We observed that miR-124 inhibition resulted in decreased larval swimming and gut contractions, indicating potential neuronal defects. miR-124 inhibition also led to a decrease in mature neurons and a concurrent increase in neuronal progenitor cells. We identified that removal of miR-124's suppression of NeuroD1 is sufficient to induce similar swimming and gut contraction defects as in miR-124 inhibitor injected embryos. Additionally, we also observed miR-124 to play a novel role in regulating the differentiation of mesodermally-derived immune cells. The sea urchin immune cells consist of blastocoelar cells (BCs) and pigment cells (PCs), which are derived from the same progenitor cells that make a binary fate decision to differentiate into BCs or PCs. miR-124 inhibition resulted in an ectopic increase in BC-specific gene expression and a concurrent decrease in differentiated PCs. In summary, we identified miR-124 to directly suppress NeuroD1, Nodal, and a BC-specific transcription factor Ese to modulate neural differentiation, as well as mesodermal development. We will systematically examine the function of miR-124 in the specification, differentiation, and maturation of neurons. These results may potentially contribute to our understanding of neurological disorders as well as neurodegenerative diseases. Also, we will identify miR-124's novel role in mesodermal differentiation and apply this knowledge to understand development in other organisms.

MicroRNA-124 has a dual role to modulate neurogenesis and mesodermal specification

Early-life immune activation is linked to increased risk for male-biased developmental disorders such as Autism Spectrum Disorder, ADHD, and Schizophrenia. These disorders are associated with hippocampal deficits in learning and cognition. We have found that immune activation with lipopolysaccharide (LPS; 100ug/ml/kg) on postnatal day (P) 21 produces hippocampal-dependent learning deficits in context fear conditioning from P24-P26, in both male and female rats. This suggests P21-P24 may be a critical window for the ontogeny of spatial learning and requisite formation of its underlying circuits. Connections between medial prefrontal cortex, dorsal hippocampus, and ventral hippocampus have been implicated in context fear learning. Few studies have examined the effects of immune activation on white matter growth across juvenile development, and its associated behavioral and cognitive implications. Our goal is to use diffusion tensor imaging (DTI) to characterize the effects of LPS immune activation on white matter development across these brain regions underlying context fear learning. Preliminary analyses show that, in non-treated rats, dorsal hippocampus axial diffusivity increases from P16 to P20 and P24, suggesting increased axonal density or myelination. Moreover, ventral hippocampus radial diffusivity increases from P16 to P24, suggesting decreased axonal density. These findings suggest that dorsal hippocampal circuits are being formed from P16 to P24, whereas ventral hippocampus circuits are being refined from P16 to P24. Future studies will examine the effects of P21 LPS immune activation on white matter microstructure at P24 and its implications for context learning.

Ex-vivo Diffusion Tensor Imaging to Examine the Development of Circuits Underlying Context Fear Conditioning

Along with genetic risk factors there also are perinatal environmental factors that contribute to the risk of developing Autism Spectrum Disorder. These environmental factors are known to activate the immune system, such that dysregulation of the immune system early in life may have negative consequences on neural function and the development of appropriate social behavior. Our experiment is designed with the intent of modeling the multitude of social behavior deficits seen in many neurodevelopmental disorders. Microglia release inflammatory cytokines in response to an immune challenge throughout which in effect “primes” them. The exaggerated cytokine release from the microglia, as well as a second “hit” later in life, alters neuronal function and leads to behavioral disorders. Our model introduces an immune challenge to rats on day 4 of life (P4) and then again on day 25 (P25), known as a “two-hit model of neuroinflammation”. Play behaviors such as pouncing, pinning, and chasing were observed and analyzed in juvenile male and female test rats. With this data we can observe the differences in the participation vs initiation in a play bout with our experimental animals compared to controls. Additionally, we are interested in the impact our model has on dopamine receptors as dopamine plays a crucial role in reward and is important for the expression of social play. Dopamine receptor expression was quantified by examining the relative gene expression of D1R and D2R within the amygdala and mPFC at 4, 24, and 72 hours post P25 injection. Results are showing a main effect of sex in the amygdala of D2R and a sex x P4 injection interaction of D1R of amygdala and mPFC. By looking at this data we can further investigate the differences present between the sexes. Funding: NIH R01MH16553 to JMS.

The effect of neuroimmune dysregulation on dopamine receptors and social play behaviors of male and female juvenile rats

UD Mass Spectrometry Core Facility

Evidence suggests that microglia, the immune cells of the brain, have an important role in the development of brain circuits. As a result, activation of the immune system early in life significantly increases the risk of various neurodevelopmental disorders, including Autism Spectrum Disorder. Perinatal exposure to infectious pathogens is suggested to be an environmental risk factor that has a role in activating the developing immune system, and the subsequent onset of neurodevelopmental diseases. Furthermore, the “two-hit hypothesis of immune activation” suggests that multiple exposures to immune activation further increases the risk of neurodevelopmental disorders. Immune activation during a “sensitive period” of neurodevelopment may result in an exaggerated response to subsequent immune challenges and the onset of behavioral disorders during the juvenile period. Additionally, microglia number and activation profiles differ between males and females during early development. Thus, males might be more susceptible to the consequences of immune activation as a result of the two-hit model. In order to better understand the two-hit model of neuroinflammation and its effect on the expression of social behaviors in males and females, we tested the impact of neonatal bacterial infection (E.coli) and a subsequent juvenile immune challenge (lipopolysaccharide, LPS) on two tests of rodent social behavior - social interaction and social recognition. The results from hand-scoring the time spent interacting in each test revealed that female control animals were not performing the test above chance. Therefore, we were interested in measuring the overall locomotive activity of test rats. Using an open-source ImageJ plugin, MouBeAt, locomotive behavior parameters were examined. Preliminary analysis of the data thus far indicates that the timing (neonatal or juvenile) and nature (E.coli or lipopolysaccharide) of the neuroimmune activation have a different effect on the expression of locomotive activity in male and female juvenile rats during a social behavior test.

Locomotive activity and sociability in male and female juvenile rats following mild immune activation

Acetylcholine (ACh) released from motor neurons activates postsynaptic ionotropic ACh receptors (AChRs), resulting in an electrical signal that leads to muscle contraction. Formation and maintenance of the neuromuscular junction is required for proper ACh signaling. Conventionally, HMTs act in the nucleus to methylate histones. Surprisingly, we found that C. elegans tropomyosin, which acts in the cytoplasm to regulate muscle contraction and stabilize actin filaments, was methylated by a HMT. In C. elegans, actin rich muscle arms extend from the body-wall muscles to the nerve cord, allowing the muscle cell to be innervated. This led us to hypothesize that cytoplasmic HMT activity regulates actin filaments and neuromuscular junction structure. Previously, tropomyosin mutants were shown to have fewer and wider muscle arms compared to wildtype. We performed extensive imaging of muscle arms in HMT mutants using confocal microscopy and observed that the HMT mutant exhibited significantly wider muscle arms compared to wild type but had no difference in muscle arm number per muscle. We then used tropomyosin RNA interference (RNAi) to knock down tropomyosin in the HMT mutant to determine if the loss of HMT and tropomyosin has an additive effect on muscle arm phenotype. After extensive muscle arm imaging and analysis, it appears that the HMT mutant grown on tropomyosin RNAi has significantly wider and fewer muscle arms per muscle compared to wildtype. This indicates that HMT and tropomyosin function together as the muscle arm phenotype observed is the same as the tropomyosin knockdown. In conclusion, our results suggest that a HMT plays a novel cytoplasmic role to control muscle development and function.

A Cytoplasmic Role for a Histone Methyltransferase in C. elegans Muscle Development

Microglia, the resident immune cells of the brain, interact with neurons to shape cognitive development. Microglial activation during the early postnatal period has been linked to long-term effects on cognition and learning in rats. We seek to examine the role of microglia in hippocampal learning by establishing a method to selectively deplete microglia in the dorsal hippocampus during a unique juvenile period development in rats. Liposome-encapsulated clodronate (LEC) is a drug that is selectively ingested by and results in the death of phagocytic cells. We infused 3 microliters LEC bilaterally into the dorsal hippocampus (dHP) of male and female rats (Sprague-Dawley) at P16 to determine whether LEC selectively depletes microglia during a period of hippocampal development. We utilized immunohistochemical (IHC) staining and RT-PCR to examine changes in microglia density and gene expression in the CA1, CA3, and dentate gyrus (DG) subregions of dorsal and ventral hippocampus (vHP) on P21, P24, P27, P30, and P40. Iba1 stain for microglia revealed that LEC significantly decreased the percent area of microglia density and the number of microglia cells per area of microglia in subregions CA1 and DG of dHP from P21-P30. LEC did not significantly deplete microglia in any vHP subregions, nor the CA3 subregion of dHP, which indicate that the spread of LEC does not go beyond the intended target of dHP CA1 and DG subregions. Future research will use this data to establish a timeline of microglial depletion during the juvenile period in order to investigate the role of microglia in hippocampal learning deficits following immune activation.

Quantification of microglia in the dorsal hippocampus following temporary intra-hippocampal microglia depletion during development

Prenatal alcohol exposure (PAE) causes a spectrum of physical, cognitive, and behavioral deficits in offspring and these disorders are categorized under the umbrella term Fetal Alcohol Spectrum Disorders (FASD). FASD affect at least 2-5% of births in the United States, making it the primary cause of preventable developmental abnormalities (May et al., 2009). PAE prevents the proper development of the corpus callosum (CC), the largest white matter tract in the brain, in adolescence which impairs cognition and behavior (Wozniak et al., 2019; Riley et al., 1995). Axonal myelination of CC, beginning in the third trimester of pregnancy and terminating in young adulthood, is particularly vulnerable to the teratogenicity of PAE. Using a rodent model of third trimester equivalent AE, our study examines longitudinal alterations to CC myelination in the adolescent AE brain. These findings will be used to assess the efficacy of a targeted adolescent exercise intervention on restoring CC myelination in our rodent model of FASD. Aerobic exercise is a known stimulator of myelinogenesis. Male and female Long-Evans rat pups were either administered alcohol via intragastric intubation in a third trimester binge model of FASD [5.25 g/kg/day on postnatal days (PD) days 4-9] or were sham-intubated as controls. On PD 30, half of all rats were housed for twelve days in modified cages equipped with a metal running wheel. All rats, including homecage controls, remained socially-housed during the entirety of the experiment. Diffusion Tensor Imaging (DTI) scans were acquired on PD 30 and 42 for rats in all groups. Preliminary analysis of DTI scans reveals that third trimester AE delays CC myelination in adolescence, supporting the clinical literature. Neither exercise intervention nor sex had a main effect on CC myelination. Immunocytochemical and electron microscopic analysis of brain tissue samples will validate these findings.

Volume and Myelination of the Corpus Callosum in a Third Trimester Model of Fetal Alcohol Spectrum Disorders: Does Voluntary Aerobic Exercise Matter?

Over recent years there has been a great surge in interest, knowledge, and technology surrounding genetics and genetic services. As a result, genetic counseling has become a rapidly growing field of medicine. In 1988, Harris’s pioneering manuscript “Genetic Counselling and the New Genetics” envisioned the future of genetic counseling as one “confirming clinical diagnoses, recognizing genetic heterogeneity, assessing risk, and providing a link between laboratories, physicians, and patients.” Today, genetic testing is a powerful tool that can be used to help direct precision medicine. Diseases and disorders that are caused by abnormalities in an individual's genome are currently classified into four categories: single-gene, multifactorial, chromosomal, and mitochondrial. This state-of-the-art review focuses on how diseases and disorders caused by genomic abnormalities are linked to neurobiological differences. Further, the review aims to provide insights into how to link laboratories, physicians, and patients to bridge the gap between genetics and neurobiology.

Next from Delaware Neuroscience Symposium 2021

Understanding Risk Factors for Postpartum Depression using the PRAMS Dataset

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