Cardiomyocyte Deletion of \u3ci\u3eBmal1\u3c/i\u3e Exacerbates QT- and RR-Interval Prolongation in \u3ci\u3eScn5a\u3c/i\u3e\u3csup\u3e+/ΔKPQ\u3c/sup\u3e Mice

Circadian rhythms are generated by cell autonomous circadian clocks that perform a ubiquitous cellular time-keeping function and cell type-specific functions important for normal physiology. Studies show inducing the deletion of the core circadian clock transcription factor Bmal1 in adult mouse cardiomyocytes disrupts cardiac circadian clock function, cardiac ion channel expression, slows heart rate, and prolongs the QT-interval at slow heart rates. This study determined how inducing the deletion of Bmal1 in adult cardiomyocytes impacted the in vivo electrophysiological phenotype of a knock-in mouse model for the arrhythmogenic long QT syndrome (Scn5a+/ΔKPQ). Electrocardiographic telemetry showed inducing the deletion of Bmal1 in the cardiomyocytes of mice with or without the ΔKPQ-Scn5a mutation increased the QT-interval at RR-intervals that were ≥130 ms. Inducing the deletion of Bmal1 in the cardiomyocytes of mice with or without the ΔKPQ-Scn5a mutation also increased the day/night rhythm-adjusted mean in the RR-interval, but it did not change the period, phase or amplitude. Compared to mice without the ΔKPQ-Scn5a mutation, mice with the ΔKPQ-Scn5a mutation had reduced heart rate variability (HRV) during the peak of the day/night rhythm in the RR-interval. Inducing the deletion of Bmal1 in cardiomyocytes did not affect HRV in mice without the ΔKPQ-Scn5a mutation, but it did increase HRV in mice with the ΔKPQ-Scn5a mutation. The data demonstrate that deleting Bmal1 in cardiomyocytes exacerbates QT- and RR-interval prolongation in mice with the ΔKPQ-Scn5a mutation

Investigating the Effects of Homocysteine as an Agonist on Invertebrate Glutamatergic Synapses

Hyperhomocysteinemia (HHcy) in mammals can produce neurological deficits, such as memory loss. The cause of the neurological issues is assumed to be due to homocysteine (HCY) binding to glutamatergic receptors in the central nervous system (CNS). High levels of HCY in the CNS are also associated with Amyotrophic Lateral Sclerosis (ALS) and Parkinson’s disease. Thus, understanding the detailed mechanisms of HCY in model preparations could be useful in developing potential treatments to neurodegenerative diseases with overlapping symptoms to HHcy. The aim of this study is to investigate the efficacy of HCY as an agonist at glutamatergic synapses in invertebrates. The glutamatergic synapses of the larval Drosophila melanogaster (D. melanogaster) and Procambarus clarkii (P. clarkii) neuromuscular junctions (NMJs) were utilized to examine the effects of applying HCY. Measurements of evoked synaptic transmission in both preparations revealed that 100 mM of HCY did not have any consistent effect. The expectation was that the acute action of HCY would have activated the glutamate receptors and then desensitized them so evoked transmission would be blocked. The pharmacological receptor profile of these NMJ receptors are of a quisqualate subtype and not a kainate, α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA) or N-methyl-D-aspartate receptor (NMDA) subtype. Consequently, HCY may not have any action on quisqualate glutamate receptor subtypes. The findings of this experiments could provide clinical implications regarding relevant pharmacological treatments in neurodegenerative diseases such as amyotrophic lateral sclerosis (ALS) and Parkinson’s disease

Effects of Clove Oil (Eugenol) on Proprioceptive Neurons, Heart Rate, and Behavior in Model Crustaceans

Clove oil contains eugenol as an active ingredient and is used as a topical anesthetic in mammals to remedy pain and to anesthetize fish and other seafood for short periods; however, the exact mechanism of action of eugenol is not fully understood. We examined use of eugenol as a reversible anesthetic in crustaceans by examining its effect on sensory and motor neurons in the Red Swamp crayfish (Procambarus clarkii), Blue crab (Callinectes sapidus) and Whiteleg shrimp (Litopenaeus vannamei) with electrophysiological recordings. The neurogenic heart rate in the three species was also monitored along with behaviors and responsiveness to sensory stimuli. The activity of the primary proprioceptive neurons was reduced at 200 ppm and ceased at 400 ppm for both crayfish (i.e., muscle receptor organ) and crab (i.e., leg PD organ) preparations when exposed to saline containing eugenol. Flushing out eugenol resulted in recovery in the majority of the preparations within five to ten minutes. Administering eugenol to crayfish and crabs both systemically and through environmental exposure resulted in the animals becoming lethargic. Direct injection into the hemolymph was quicker to decrease reflexes and sensory perception, but heart rate was still maintained. Eugenol at a circulating level of 400 ppm decreased electromyogram activity in the claw muscle of crabs. Surprisingly, this study found no change in heart rate despite administering eugenol into the hemolymph to reach 400 ppm in crabs or crayfish but heart rate in shrimp preparations decreased. Our results demonstrate the feasibility of eugenol as a short-term anesthetic for crustaceans to decrease stress during handling or transportation, considering its effectiveness at decreasing sensory input and the quick recovery of upon removal of eugenol. A neurophysiology course took this project on as an authentic course-based undergraduate research experience (ACURE)

Disrupting the Circadian Clock Mechanism in Cardiomyocytes Exacerbates the LQT3-related phenotype in Scn5a(ΔKPQ/+) Mice

Introduction: The pro-arrhythmic LQTS type 3 (LQT3) is caused by gain-of-function mutations in the cardiac Na+ channel Scn5a. LQT3 patients typically have an abnormally long heart rate-corrected QT-interval (QTc), but even patients with the same disease-causing mutation show a wide range of clinical phenotypes. This suggests additional factors influence the LQT3-related phenotype. Hypothesis: Many LQT3 patients show an increased incidence in life-threatening arrhythmias at night. We tested the hypothesis that disruption of the cardiomyocyte molecular clock that underlies circadian rhythms modifies the LQT3-related phenotype. Methods: We used in vivo ECG telemetry of control mice and mice that harbor an LQT3-causing mutation (Scn5aΔKPQ/+). All animals were genetically engineered to enable us to induce the deletion of Bmal1, a key component of the molecular clock, in adult cardiomyocytes. We calculated the RR-interval, QT-interval, and the QTc-interval using the correction formula from Mitchell et al. AJP 1998. Results: Before Bmal1 deletion, Scn5aΔKPQ/+ mice showed a prolongation in the RR, QT and QTc-intervals compared to control animals. Bmal1 deletion slowed the RR and QT-intervals in both groups, but the QTc-interval remained unchanged. Linear regression analysis revealed that the slope of the QT-RR relation in Scn5aΔKPQ/+ mice was double that of control animals and Bmal1 deletion increased the slope in both groups. Additionally, Bmal1 deletion lengthened the QT-interval at a lower RR-interval in Scn5aΔKPQ/+ animals compared to control. Conclusion: Inducing Bmal1 deletion in control and Scn5aΔKPQ/+ mice did not change the QTc interval, but increased the slope of the QT-RR relation so at slower RR-intervals there is a greater change in the QT-interval. Scn5aΔKPQ/+ mice showed the greatest QT prolongation at slow RR-intervals. We conclude that disruption in the molecular clock mechanism exacerbates the LQT3-related phenotype, especially at slow heart rates

Von der Ethnogenese zur Identitätsforschung

Hyperhomocysteinemia (HHcy) in mammals can produce neurological deficits, such as memory loss. The cause of the neurological issues is assumed to be due to homocysteine (HCY) binding to glutamatergic receptors in the central nervous system (CNS). High levels of HCY in the CNS are also associated with Amyotrophic Lateral Sclerosis (ALS) and Parkinson’s disease. Thus, understanding the detailed mechanisms of HCY in model preparations could be useful in developing potential treatments to neurodegenerative diseases with overlapping symptoms to HHcy. The aim of this study is to investigate the efficacy of HCY as an agonist at glutamatergic synapses in invertebrates. The glutamatergic synapses of the larval Drosophila melanogaster (D. melanogaster) and Procambarus clarkii (P. clarkii) neuromuscular junctions (NMJs) were utilized to examine the effects of applying HCY. Measurements of evoked synaptic transmission in both preparations revealed that 100 mM of HCY did not have any consistent effect. The expectation was that the acute action of HCY would have activated the glutamate receptors and then desensitized them so evoked transmission would be blocked. The pharmacological receptor profile of these NMJ receptors are of a quisqualate subtype and not a kainate, α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA) or N-methyl-D-aspartate receptor (NMDA) subtype. Consequently, HCY may not have any action on quisqualate glutamate receptor subtypes. The findings of this experiments could provide clinical implications regarding relevant pharmacological treatments in neurodegenerative diseases such as amyotrophic lateral sclerosis (ALS) and Parkinson’s disease