The Drosophila melanogaster heart is a popular model in which to study cardiac physiology and development. Progress has been made in understanding the role of endogenous compounds in regulating cardiac function in this model. It is well characterized that common neurotransmitters act on many peripheral and non-neuronal tissues as they flow through the hemolymph of insects. Many of these neuromodulators, including acetylcholine (ACh), have been shown to act directly on the D. melanogaster larval heart. ACh is a primary neurotransmitter in the central nervous system (CNS) of vertebrates and at the neuromuscular junctions on skeletal and cardiac tissue. In insects, ACh is the primary excitatory neurotransmitter of sensory neurons and is also prominent in the CNS. A full understanding regarding the regulation of the Drosophila cardiac physiology by the cholinergic system remains poorly understood. Here we use semi-intact D. melanogaster larvae to study the pharmacological profile of cholinergic receptor subtypes, nicotinic acetylcholine receptors (nAChRs) and muscarinic acetylcholine receptors (mAChRs), in modulating heart rate (HR). Cholinergic receptor agonists, nicotine and muscarine both increase HR, while nAChR agonist clothianidin exhibits no significant effect when exposed to an open preparation at concentrations as low as 100 nM. In addition, both nAChR and mAChR antagonists increase HR as well but also display capabilities of blocking agonist actions. These results provide evidence that both of these receptor subtypes display functional significance in regulating the larval heart's pacemaker activity.

Sleep disturbances are a common early symptom of neurodegenerative diseases, including Alzheimer's disease (AD) and other age-related dementias, and emerging evidence suggests that poor sleep may be an important contributor to development of amyloid pathology. Of the causes of sleep disturbances, it is estimated that 10%-20% of adults in the United States have sleepdisordered breathing (SDB) disorder, with obstructive sleep apnea accounting for the majority of the SBD cases. The clinical and epidemiological data clearly support a link between sleep apnea and AD; yet, almost no experimental research is available exploring the mechanisms associated with this correlative link. Therefore, we exposed an AD-relevant mouse model (APP/PS1 KI) to chronic intermittent hypoxia (an experimental model of sleep apnea) to begin to describe one of the potential mechanisms by which SDB could increase the risk of dementia. Previous studies have found that astrogliosis is a contributor to neuropathology in models of chronic intermittent hypoxia (IH) and AD; therefore, we hypothesized that a reactive astrocyte response might be a contributing mechanism in the neuroinflammation associated with sleep apnea. To test this hypothesis, 10-11-month-old wild type (WT) and APP/PS1 KI mice were exposed to 10 hours of IH, daily for four weeks. At the end of four weeks brains were analyzed from amyloid burden and astrogliosis. No effect was found for chronic IH exposure on amyloid-beta levels or plaque load in the APP/PS1 KI mice. A significant increase in GFAP staining was found in the APP/PS1 KI mice following chronic IH exposure, but not in the WT mice. Profiling of genes associated with different phenotypes of astrocyte activation identified GFAP, CXCL10, and Ggta1 as significant responses activated in the APP/PS1 KI mice exposed to chronic IH.

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Translating spinal cord injury (SCI) therapies which promote axonal regeneration from preclinical animal models into the human population is challenging. One potential obstacle is that human genetic predispositions may limit the efficacy of such experimental treatments. The clinically relevant ApoE4 (E4) allele, present in about 14% of the human population, corresponds to an increased incidence of Alzheimer's disease—however, its role in recovery from SCI is poorly understood despite suggestive data implicating its involvement. Indeed, two clinical studies found that SCI individuals with the E4 allele had less motor recovery than individuals without the allele despite longer time in rehabilitation. ApoE4 may mediate this diminished recovery by limiting regeneration and sprouting. Robust regeneration is energy intensive and requires efficient mitochondria, and studies have shown that ApoE4 impairs mitochondrial function. Given these mitochondrial deficits, we hypothesize that ApoE4 can impair regeneration and sprouting. To test this hypothesis, we investigated the impact of ApoE4 on sprouting and neurite outgrowth. In our experiments, we cultured dorsal root ganglia neurons from mice expressing human ApoE isoforms—ApoE2 (E2), ApoE3 (E3), or ApoE4—under the control of the endogenous mouse ApoE promoter. We then analyzed differences in 1) neurite complexity and 2) robustness of outgrowth between genotypes. In two of three independent experiments, E4 neurons had decreased neurite outgrowth and decreased neurite branching compared to E2 and E3 neurons. Data from the Spot Assay, an in vitro model of the glial scar and CNS regeneration, also suggest that chondroitin sulfate proteoglycans may inhibit regeneration in E4 neurons to an even greater extent than in E3 neurons. In addition, with preliminary in vivo data, we are beginning to characterize serotonergic sprouting after lateral C2 hemisection in mice of each ApoE genotype. Since outgrowth, sprouting, and regeneration all partially mediate recovery after CNS injury, impairments in these processes can adversely affect recovery. These foundational studies address not only the possible genetic influence of ApoE4 on recovery from CNS injury, but also a critical gap in knowledge—whether there is a genetic contribution underlying responses to treatment in SCI individuals.Support or Funding InformationUniversity of Kentucky Startup FundsThis abstract is from the Experimental Biology 2019 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.