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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.

Delaware Neuroscience Symposium 2021

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

technical paper

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.

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.

Genes, Brains, and Behavior: Genetic counselors’ role in precision medicine

Early life experiences shape neurodevelopmental, epigenetic, and future behavioral landscapes of individuals. While both animal models and human twin studies suggest that there is a predisposition for certain stimuli to be innately fear-inducing, molecular mechanisms remain poorly understood. Prior work in our laboratory has demonstrated that administering TMT (2,5-dihydro-2,4,5-trimethylthaizonline), a synthetic odorant from fox feces, induces robust freezing in naïve rodents without any prior learning. However, experiencing predator odor during early development alters the response later in life, suggesting a change in perception of the innate fear-inducing odor. Administering TMT to dams and pups during development (PN1-21) inside the home-cage alters the quality of maternal care, pup ultrasonic-vocalizations, and lowers freezing (PN30) upon re-exposure comparable to control animals. To extend these findings to other predator odorants and examine how maternal behavior may alter later innate fear responses, pups with or without their dam were exposed to either a noxious control (butyric acid) or a bobcat urine for 20 minutes in their home-cage for the first 21 days of life. Concurrent with odor exposures, video and USV recordings were captured to quantify maternal care and pup behavior, respectively. On PN30, rodents were exposed to bobcat urine for 10 minutes and freezing behavior was recorded. Finally, on PN35, to examine if fear behaviors were generalized to other paradigms, an open-field test was administered. Preliminary results suggest that developmental exposure to bobcat urine lowered the quality of maternal care and increased freezing upon re-exposure on PN30. There were no differences in open-field behavior or pup ultrasonic vocalizations. These results support the complex relationship of early exposure to predator stimuli, effects of maternal behavior, and the expression of innate fear later in life. Future research will examine epigenetic alterations linked to long lasting changes in fear responses from early experience with predator odors.

Impact of developmental exposure to predator urine on maternal behavior and the expression of innate fear

The pain of Black Americans is historically underdiagnosed and undertreated (Anderson, Green, & Payne, 2009). While many structural and individual level factors associated with a history of, and ongoing medical racism contribute to these disparities (Gee & Ford, 2011; Feagin & Bennefield, 2014) recent work has demonstrated that these disparities are also evident at the level of face and emotion perception and contribute to disparities in care (Mende-Siedlecki, 2019). The present work examines whether perceiver deficits in pain recognition are reflected in divergent neural activity in regions associated with face processing, pain, and empathy. Replicating previous work, we find that participants had higher thresholds for perceiving pain on Black male vs White male faces, such that more pain needed to be expressed on Black male faces to be seen as equivalent to White male pain. In turn, we find that Black males were prescribed less pain-relieving cream than White males overall. Moreover, we find that perceptual bias continued to facilitate the effect of target race on treatment when status/strength stereotypes and explicit racial bias were included as competing within-subjects mediators. Finally, we find differential activity in posterior STS and ATL associated with increasing pain on White vs Black faces, which overlap with face selective regions identified by a face localizer as well as the broader literature.

Neural Underpinnings of Racial Bias in Pain Perception & Treatment

Several studies have shown that receiving speech or language services for expressive language delays positively impacts academic indices of success (e.g., Del Tufo, Earle, & Cutting, 2019). However, beyond expressive language delays we do not know if receiving services before the age of 5 has a positive impact on academic performance. Expressive language refers to the production of spoken language, and the milestones of expressive language, such as the onset of babbling, production of first words, and putting several words together, are early indicators of normal language development. We analyzed a national sample of data (National Survey of Children’s Health, 2011/2012) of children 0-17 years of age, through cross-sectional, telephone-based interviews to determine the (1) factors that impact whether or not a child will receive speech and/or language services before the age of 5, and (2) the impact of receiving speech and/or language services on the indices of academic success. To answer the aforementioned questions we implemented hierarchical logistic regression and linear regression, respectively. The results indicate that several factors beyond expressive language impact children’s receipt of speech and/and language services before age 5. These factors include sex of the child, socioeconomic status, period of gestation, and parent’s concerns regarding receptive language. These factors together predicted if a child would receive speech and/or language, which, in turn, had an impact on academic performance.

Which factors beyond expressive language delays lead to the receipt of speech and/or language services before age 5?

Alcohol exposure (AE) during pregnancy is known to affect fetal medial prefrontal cortex (mPFC) and hippocampus (HC) development. Previous work has demonstrated that these two structures are vulnerable to AE during the brain growth spurt, which occurs during 3rd trimester of human pregnancy and the first two postnatal weeks in rodents. Our lab has shown that thalamic nucleus reuniens (Re) is damaged in a rodent model of human 3rd trimester AE. We have also shown that Re is critical for mPFC–HC oscillatory synchrony and spatial working memory (SWM). The current study investigated the effects of early AE on SWM ability in adulthood in rats. We predicted that AE would lead to SWM impairment that worsened as working memory demand increased. We administered 5.25 g/kg/day of ethanol in milk formula via intragastric intubations in a binge manner on PD 4-9 (AE group) or performed intubations without liquid (sham intubated (SI) group). On PD90, rats were trained on a continuous alternation (CA) T-maze task. Upon reaching a choice accuracy criterion of 80% for two consecutive days on CA, we introduced a delay between trials (DA) in order to increase SWM demand. The rats underwent 6 DA sessions, consisting of 12 each of 10-second (s), 30 s, and 60 s delay trials given in a pseudorandom sequence. Our results show that animals in both AE and SI groups learned the CA task at similar rates. However, on the DA task, the SI group showed consistent improvement across sessions on the 30-s delay trials, whereas the AE group did not (postnatal - treatment x day interaction: F(5,195)=2.70, p = .02). For the 10 s delay trials, both AE and SI groups showed improvement across days (main effect of day: F(5,195)=7.93 , p < .001), whereas for the 60 s delay trials, both groups performed uniformly poorly across days. These findings support the hypothesis that binge AE during the brain growth spurt produces SWM deficits that depend on SWM demand. This study will lead to a better understanding of the impact of HC-Re-mPFC circuitry damage due to developmental AE on cognitive function later in life.

Delay-dependent spatial working memory deficits in a rat model of third trimester alcohol exposure.

Aversive caregiving in early life is a risk factor for aberrant brain and behavioral development throughout the lifespan. This outcome is related to aberrant epigenetic regulation of the Bdnf gene. The Bdnf gene encodes for brain-derived neurotrophic factor (BDNF), a neurotrophin involved in neural plasticity, learning, and memory. Disruptions in caregiver-infant interactions lead to increased methylation and decreased expression of the Bdnf gene. One way to mitigate this effect is hypothesized to be through aerobic exercise. Exercise increases BDNF at the protein and gene expression levels, making it an exciting target for therapeutic interventions. To our knowledge, exercise has never been studied as a therapeutic intervention in preclinical rodent models of early life maltreatment. To that end, the current study is investigating the effect of an adult voluntary wheel running intervention on Bdnf aberrant methylation and expression in the prefrontal cortex of rats who experienced aversive caregiving in infancy. This study presents novel findings on the mechanisms underlying neural plasticity in the prefrontal cortex in an early life stress context.

Mitigating the Epigenetic Consequences of Early Life Stress with a Behavioral Intervention

In adolescents, low sleep duration is associated with psychiatric disorders, cognitive problems (Cheng et al., 2020), and diminished academic performance (Eliasson et al., 2002). This is particularly problematic for racial and ethnic minority adolescents, who are at increased risk of low sleep duration (Singh et al., 2013). While adolescent racial and ethnic low sleep duration has been linked to socioeconomic status (Gugllelmo et al., 2018), physical activity in girls (Bates et al., 2016), and school engagement (Dunbar, Mirpuri, & Yip, 2017), all four factors have not yet been explored together. The current study aims to understand the physiological impact of stress on sleep, which in turn is expected to impact behavior and development differentially by race and ethnicity. The present study will include participants from the National Institute of Health Adolescent Brain Cognitive Development (ABCD) Study. Resting-state neuroimaging data will be used to explore differences in intrinsic connectivity. The results of the current study have the potential to bring to light protective factors: factors that reduce the effects of stress on sleep.

Sleep Disparities in Adolescents

Individuals with chronic stroke affecting the corticospinal track often show severe motor impairment or paralysis of hand. Functional magnetic resonance imaging (fMRI) studies have shown that this impairment corresponds to in a reduction in bold activity in the lesioned hemisphere. It still unclear whether this reduction of brain activity also correspond to changes in the cortical representation of this body part in the motor cortex or whether this representation is preserved. To explore this issue, two individuals with subcortical stroke and paralysis of the hand were presented with an fMRI experiment in which they were asked to move (or to imagine for the paralyzed hand) each digit of hand following a random sequence. Representation similarity analysis was used to explore whether the pattern of activations across fingers in the motor cortex differed, indicating a maintained representation of the hand, or was similar, indicating damage to this representation. Both individuals showed finger differentiation in the ipsilateral M1 and one individual showed differentiation also in the contralateral hemisphere. These results suggest that the representation of the hand in M1 is maintained in individuals with corticospinal damage despite the complete paralysis of the hand, providing important clinical implications for rehabilitation.

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

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