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Potter S, Sifers J, Yocom E, Blümich SLE, Potter R, Nadolski J, Harrison DA, Cooper RL. Effects of inhibiting mTOR with rapamycin on behavior, development, neuromuscular physiology and cardiac function in larval Drosophila. Biol Open 2019; 8:bio.046508. [PMID: 31704693 PMCID: PMC6899040 DOI: 10.1242/bio.046508] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/17/2022] Open
Abstract
Rapamycin and other mTOR inhibitors are being heralded as possible treatments for many human ailments. It is currently being utilized clinically as an immunomodulator after transplantation procedures and as a treatment for certain forms of cancer, but it has numerous potential clinical indications. Some studies have shown profound effects on life cycle and muscle physiology, but these issues have not been addressed in an organism undergoing developmental processes. This paper fills this void by examining the effect of mTOR inhibition by rapamycin on several different qualities of larval Drosophila. Various dosages of the compound were fed to second instar larvae. These larvae were monitored for pupae formation to elucidate possible life cycle effects, and a delay to pupation was quantified. Behavioral deficits were documented in rapamycin-treated larvae. Electrophysiological measurements were taken to discern changes in muscle physiology and synaptic signaling (i.e. resting membrane potential, amplitude of excitatory post-synaptic potentials, synaptic facilitation). Pupation delay and effects on behavior that are likely due to synaptic alterations within the central nervous system were discovered in rapamycin-fed larvae. These results allow for several conclusions as to how mTOR inhibition by rapamycin affects a developing organism. This could eventually allow for a more informed decision when using rapamycin and other mTOR inhibitors to treat human diseases, especially in children and adolescents, to account for known side effects. Summary: Inhibiting mTOR by rapamycin delays pupation, reduced body wall contractions and mouth-hook movements while synaptic transmission appeared normal in larval Drosophila.
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Affiliation(s)
- Samuel Potter
- Deptartment of Biology and Center for Muscle Biology, University of Kentucky, Lexington, KY, 40506, USA
| | - Jacob Sifers
- Deptartment of Biology and Center for Muscle Biology, University of Kentucky, Lexington, KY, 40506, USA.,Alice Lloyd College, 100 Purpose Road, Pippa Passes, KY, 41844, USA
| | - Emily Yocom
- Deptartment of Biology and Center for Muscle Biology, University of Kentucky, Lexington, KY, 40506, USA.,Kentucky Wesleyan College, Owensboro, KY, 42301, USA
| | - Sandra L E Blümich
- Deptartment of Biology and Center for Muscle Biology, University of Kentucky, Lexington, KY, 40506, USA.,Veterinärmedizinische Fakultät, Universität Leipzig, Leipzig, Germany
| | - Rachel Potter
- Deptartment of Biology and Center for Muscle Biology, University of Kentucky, Lexington, KY, 40506, USA
| | - Jeremy Nadolski
- Department of Mathematical and Computational Sciences, Benedictine University, Lisle, IL, 60532 , USA
| | - Douglas A Harrison
- Deptartment of Biology and Center for Muscle Biology, University of Kentucky, Lexington, KY, 40506, USA
| | - Robin L Cooper
- Deptartment of Biology and Center for Muscle Biology, University of Kentucky, Lexington, KY, 40506, USA
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Wu WH, Cooper RL. Serotonin and synaptic transmission at invertebrate neuromuscular junctions. Exp Neurobiol 2012; 21:101-12. [PMID: 23055788 PMCID: PMC3454807 DOI: 10.5607/en.2012.21.3.101] [Citation(s) in RCA: 36] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/02/2012] [Accepted: 06/19/2012] [Indexed: 11/19/2022] Open
Abstract
The serotonergic system in vertebrates and invertebrates has been a focus for over 50 years and will likely continue in the future. Recently, genomic analysis and discovery of alternative splicing and differential expression in tissues have increased the knowledge of serotonin (5-HT) receptor types. Comparative studies can provide useful insights to the wide variety of mechanistic actions of 5-HT responsible for behaviors regulated or modified by 5-HT. To determine cellular responses and influences on neural systems as well as the efferent control of behaviors by the motor units, preparations amenable to detailed studies of synapses are beneficial as working models. The invertebrate neuromuscular junctions (NMJs) offer some unique advantages for such investigations; action of 5-HT at crustacean NMJs has been widely studied, and leech and Aplysia continue to be key organisms. However, there are few studies in insects likely due to the focus in modulation within the CNS and lack of evidence of substantial action of 5-HT at the Drosophila NMJs. There are only a few reports in gastropods and annelids as well as other invertebrates. In this review we highlight some of the key findings of 5-HT actions and receptor types associated at NMJs in a variety of invertebrate preparations in hopes that future studies will build on this knowledge base.
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Affiliation(s)
- Wen-Hui Wu
- Department of Biology & Center for Muscle Biology, University of Kentucky, Lexington, KY 40506-0225, USA
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Desai-Shah M, Cooper RL. Different mechanisms of Ca2+ regulation that influence synaptic transmission: comparison between crayfish and Drosophila neuromuscular junctions. Synapse 2010; 63:1100-21. [PMID: 19650116 DOI: 10.1002/syn.20695] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022]
Abstract
A brief historical background on synaptic transmission in relation to Ca(2+) dynamics and short-term facilitation is described. This study focuses on the mechanisms responsible for the regulation of intracellular calcium concentration ([Ca(2+)](i)) in high output terminals of larval Drosophila compared to a low-output terminal of the crayfish neuromuscular junction (NMJ). Three processes; plasmalemmal Na(+)/Ca(2+) exchanger [NCX], Ca(2+)-ATPase (PMCA), and sarcoplasmic/endoplasmic Ca(2+)-ATPase (SERCA) are important in regulating the [Ca(2+)](i) are examined. When the NCX is compromised by reduced [Na(+)](o), no consistent effect occurred; but a NCX blocker KB-R7943 decreased the excitatory postsynaptic potential (EPSP) amplitudes. Compromising the PMCA with pH 8.8 resulted in an increase in EPSP amplitude but treatment with a PMCA specific inhibitor carboxyeosin produced opposite results. Thapsigargin exposure to block the SERCA generally decreases EPSP amplitude. Compromising the activity of the above Ca(2+) regulating proteins had no substantial effects on short-term depression. The Kum(170TS) strain (with dysfunctional SERCA), showed a decrease in EPSP amplitudes including the first EPSP within the train. Synaptic transmission is altered by reducing the function of the above three [Ca(2+)](i) regulators; but they are not consistent among different species as expected. Results in crayfish NMJ were more consistent with expected results as compared to the Drosophila NMJ. It is predicated that different mechanisms are used for regulating the [Ca(2+)](i) in high and low output synaptic terminals.
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Affiliation(s)
- Mohati Desai-Shah
- Department of Biology, University of Kentucky, Lexington, Kentucky 40506-0225, USA
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Abstract
Here we present some of the key important discoveries made with the opener neuromuscular (NMJ) preparation of crustaceans and illustrate that there is still much to learn from this model preparation. In understanding the history one can appreciate why even today this NMJ still offers a rich playground to address questions regarding pre- and post-synaptic function and plasticity. The viability and ease of access to the terminal for intracellular as well as extracellular electrophysiology and imaging are significant advantages. The mechanisms behind the modulation of vesicular kinetics and fusion within the high- and low-output terminals are begging for investigation. The preparation also offers a testable model system for computational assessments and manipulations to examine key variables in theoretical models of synaptic function, for example calcium dynamics during short-term facilitation. The synaptic complexity of active zone and statistical nature of quantal release is also an open area for future investigation both experimentally and computationally.
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Affiliation(s)
- Ann S Cooper
- Department of Biology, University of Kentucky, USA
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Lee JY, Bhatt D, Bhatt D, Chung WY, Cooper RL. Furthering pharmacological and physiological assessment of the glutamatergic receptors at the Drosophila neuromuscular junction. Comp Biochem Physiol C Toxicol Pharmacol 2009; 150:546-57. [PMID: 19695344 DOI: 10.1016/j.cbpc.2009.08.002] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 05/13/2009] [Revised: 08/03/2009] [Accepted: 08/06/2009] [Indexed: 11/23/2022]
Abstract
Drosophila melanogaster larval neuromuscular junctions (NMJs) serve as a model for synaptic physiology. The molecular sequences of the postsynaptic glutamate receptors have been described; however, the pharmacological profile has not been fully elucidated. The postsynaptic molecular sequence suggests a novel glutamate receptor subtype. Kainate does not depolarize the muscle, but dampens evoked EPSP amplitudes. Quantal responses show a decreased amplitude and area under the voltage curve indicative of reduced postsynaptic receptor sensitivity to glutamate transmission. ATPA, a kainate receptor agonist, did not mimic kainate's action. The metabotropic glutamate receptor agonist t-ACPD had no effect. Domoic acid, a kainate/AMPA receptor agonist, blocks the postsynaptic receptors without depolarizing the muscle. However, SYM 2081, a kainate receptor agonist, did depolarize the muscle and reduce the EPSP amplitude at 1 mM but not at 0.1 mM. This supports the notion that these are generally a quisqualate subtype receptors with some oddities in the pharmacological profile. The results suggest a direct postsynaptic action of kainate due to partial antagonist action on the quisqualate receptors. There does not appear to be presynaptic auto-regulation via a kainate receptor subtype or a metabotropic auto-receptor. This study aids in furthering the pharmokinetic profiling and specificity of the receptor subtypes.
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Affiliation(s)
- J-Y Lee
- Department of Biology, University of Kentucky, Lexington, KY, USA 40506-0225, USA
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Tsai MC, Chen YH. (±)3,4-Methylenedioxyamphetamine elicits action potential bursts in a central snail neuron. Exp Neurol 2007; 203:423-44. [PMID: 17157297 DOI: 10.1016/j.expneurol.2006.08.027] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/23/2006] [Revised: 08/22/2006] [Accepted: 08/25/2006] [Indexed: 11/21/2022]
Abstract
The effects of (+/-)3,4-methylenedioxyamphetamine (MDA) were studied in an identifiable RP4 neuron of the African snail, Achatina fulica Ferussac, using the two-electrode voltage-clamp method. The RP4 neuron generated spontaneous action potentials. Extracellular or intracellular application of MDA elicited action potential bursts of the central RP4 neuron. The action potential bursts elicited by MDA were not blocked when neurons were immersed in high-Mg2+ solution, Ca2+-free solution, nor after continuous perfusion with atropine, d-tubocurarine, propranolol, prazosin, haloperidol, sulpiride or methiothepin. Notably, the induction of action potential bursts was blocked by pretreatment with protein kinase C (PKC) inhibitors, chelerythrine and Ro 31-8220, but not by protein kinase A (PKA) inhibitors, KT-5720 and H89, nor by the phospholipase C (PLC) inhibitor, U73122. PKC activators, i.e., phorbol 12,13-dibutyrate (PDBu) and 1-oleoyl-2-acety-sn-glycerol (OAG; a membrane-permeant DAG analog), facilitate the induction of action potential bursts elicited by MDA. Voltage-clamp studies revealed that MDA decreased the delayed rectifying K+ current (I(KD)) of the RP4 neuron. Further, although Ro 31-8220 did not affect the I(KD), Ro 31-8220 decreased the inhibitory effect of MDA on the I(KD). These results suggest that the generation of action potential bursts elicited by MDA was not due to (1) the synaptic effects of neurotransmitters, (2) the cholinergic, adrenergic, dopaminergic or serotoninergic receptors of the excitable membrane. Instead, the MDA-elicited action potential bursts are closely related to PKC activity and the inhibitory effects on the I(KD).
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Affiliation(s)
- Ming-Cheng Tsai
- Department of Pharmacology, College of Medicine, National Taiwan University, No.1, Section 1, Jen-Ai Road, Taipei, Taiwan
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Dasari S, Cooper RL. Direct influence of serotonin on the larval heart of Drosophila melanogaster. J Comp Physiol B 2005; 176:349-57. [PMID: 16362307 DOI: 10.1007/s00360-005-0058-3] [Citation(s) in RCA: 40] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/07/2005] [Revised: 11/16/2005] [Accepted: 11/23/2005] [Indexed: 12/31/2022]
Abstract
The heart rate (HR) of larval Drosophila is established to be modulated by various neuromodulators. Serotonin (5-HT) showed dose-dependent responses in direct application within semi-intact preparations. At 1 nM, HR decreased by 20% while it increased at 10 nM (10%) and 100 nM (30%). The effects plateaued at 100 nM. The action of 5-HT on the heart was examined with an intact Central Nervous System (CNS) and an ablated CNS. The heart and aorta of dorsal vessel pulsate at different rates at rest and during exposure to 5-HT. Splitting the heart and aorta resulted in a dramatic reduction in pulse rate of both the segments and the addition of 5-HT did not produce regional differences. The split aorta and heart showed a high degree of sensitivity to sham changes of saline but no significant effect to 5-HT. Larvae-fed 5-HT (1 mM) did not show any significant change in HR. Since 3,4-methylenedioxymethamphetamine (MDMA) is known to act as a weak agonist on 5-HT receptors in vertebrates, we tested an exogenous application; however, no significant effect was observed to dosage ranging from 1 nM to 100 microM in larvae with and without an intact CNS. In summary, direct application of 5-HT to the larval heart had significant effects in a dose-dependent manner while MDMA had no effect.
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Affiliation(s)
- Sameera Dasari
- Department of Biology, University of Kentucky, 675 Rose Street, Lexington, KY 40506-0225, USA
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