Direct innervation of the Drosophila melanogaster larval aorta

Conserved chamber-specific polyploidy maintains heart function in Drosophila

Developmentally programmed polyploidy (whole-genome duplication) of cardiomyocytes is common across evolution. Functions of such polyploidy are essentially unknown. Here, in both Drosophila larvae and human organ donors, we reveal distinct polyploidy levels in cardiac organ chambers. In Drosophila, differential growth and cell cycle signal sensitivity leads the heart chamber to reach a higher ploidy/cell size relative to the aorta chamber. Cardiac ploidy-reduced animals exhibit reduced heart chamber size, stroke volume and cardiac output, and acceleration of circulating hemocytes. These Drosophila phenotypes mimic human cardiomyopathies. Our results identify productive and likely conserved roles for polyploidy in cardiac chambers and suggest that precise ploidy levels sculpt many developing tissues. These findings of productive cardiomyocyte polyploidy impact efforts to block developmental polyploidy to improve heart injury recovery.

Conserved Chamber-Specific Polyploidy Maintains Heart Function in Drosophila

Developmentally programmed polyploidy (whole-genome-duplication) of cardiomyocytes is common across evolution. Functions of such polyploidy are essentially unknown. Here, we reveal roles for precise polyploidy levels in cardiac tissue. We highlight a conserved asymmetry in polyploidy level between cardiac chambers in Drosophila larvae and humans. In Drosophila , differential Insulin Receptor (InR) sensitivity leads the heart chamber to reach a higher ploidy/cell size relative to the aorta chamber. Cardiac ploidy-reduced animals exhibit reduced heart chamber size, stroke volume, cardiac output, and acceleration of circulating hemocytes. These Drosophila phenotypes mimic systemic human heart failure. Using human donor hearts, we reveal asymmetry in nuclear volume (ploidy) and insulin signaling between the left ventricle and atrium. Our results identify productive and likely conserved roles for polyploidy in cardiac chambers and suggest precise ploidy levels sculpt many developing tissues. These findings of productive cardiomyocyte polyploidy impact efforts to block developmental polyploidy to improve heart injury recovery.

Examining the effect of manganese on physiological processes: Invertebrate models

Manganese (Mn²⁺ as MnSO₄ &/or MnCl₂) is a common and essential element for maintaining life in plants and animals and is found in soil, fresh waters and marine waters; however, over exposure is toxic to organisms. MnSO₄ is added to soil for agricultural purposes and people are exposed to Mn²⁺ in the mining industry. Hypermanganesemia in mammals is associated with neurological issues mimicking Parkinson's disease (PD) and appears to target dopaminergic neural circuits. However, it also seems that hypermanganesemia can affect many aspects of health besides dopaminergic synapses. We examined the effect on development, behavior, survival, cardiac function, and glutamatergic synaptic transmission in the Drosophila melanogaster. In addition, we examined the effect of Mn²⁺ on a sensory proprioceptive organ and nerve conduction in a marine crustacean and synaptic transmission at glutamatergic neuromuscular junctions of freshwater crayfish. A dose-response effect of higher Mn²⁺ retards development, survival and cardiac function in larval Drosophila and survival in larvae and adults. MnSO₄ as well as MnCl₂ blocks stretch activated responses in primary proprioceptive neurons in a dose-response manner. Mn²⁺ blocks glutamatergic synaptic transmission in Drosophila as well as crayfish via presynaptic action. This study is relevant in demonstrating the effects of Mn²⁺ on various physiological functions in order to learn more about acute and long-term consequences Mn²⁺ exposure.

Effects of inhibiting mTOR with rapamycin on behavior, development, neuromuscular physiology and cardiac function in larval Drosophila

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.

Structural and functional characterization of the contractile aorta and associated hemocytes of the mosquito Anopheles gambiae

The primary pump of the circulatory system of insects is a dorsal vessel that traverses the length of the insect. The anterior portion, located in the head, neck and thorax, is the aorta, and the posterior portion, located in the abdomen, is the heart. Here, we characterize the structure and function of the aorta and conical chamber of the mosquito, Anopheles gambiae. The aorta begins in the head with an excurrent opening located above the dorsal pharyngeal plate and ends at the thoraco-abdominal junction where it joins the conical chamber of the heart. The aorta lacks ostia, and based on the diameter of the vessel as well as the density and helical orientation of muscle, is comprised of three regions: the anterior aorta, the bulbous chamber, and the posterior aorta. The aorta contracts in the anterograde direction, but these contractions are independent of heart contractions and do not play a major role in hemolymph propulsion. Intravital imaging of the venous channels, the first abdominal segment and the neck revealed that hemolymph only travels through the aorta in the anterograde direction, and does so only during periods of anterograde heart flow. Furthermore, hemolymph only enters the thoraco-abdominal ostia of the conical chamber when the heart contracts in the retrograde direction, propelling this hemolymph to the posterior of the body. Finally, very few hemocytes associate with the aorta, and unlike what is seen in the periostial regions of the heart, infection does not induce the aggregation of hemocytes on the aorta.

Using optogenetics to assess neuroendocrine modulation of heart rate in Drosophila melanogaster larvae

The Drosophila melanogaster heart has become a principal model in which to study cardiac physiology and development. While the morphology of the heart in Drosophila and mammals is different, many of the molecular mechanisms that underlie heart development and function are similar and function can be assessed by similar physiological measurements, such as cardiac output, rate, and time in systole or diastole. Here, we have utilized an intact, optogenetic approach to assess the neural influence on heart rate in the third instar larvae. To simulate the release of modulators from the nervous system in response to environmental influences, we have directed expression of channel-rhodopsin variants to targeted neuronal populations to assess the role of these neural ensembles in directing release of modulators that may affect heart rate in vivo. Our observations show that the activation of targeted neurons, including cholinergic, dopaminergic, and serotonergic neurons, stimulate the release of cardioactive substances that increase heart rate after the initial activation at both room temperature and in a cold environment. This parallels previous studies suggesting these modulators play a crucial role in altering heart rate when applied to exposed hearts and adds to our understanding of chemical modulation of heart rate in intact Drosophila larvae.

Biogenic amines modulate pulse rate in the dorsal blood vessel of Lumbriculus variegatus

The biogenic amines are widespread regulators of physiological processes, and play an important role in regulating heart rate in diverse organisms. Here, we present the first pharmacological evidence for a role of the biogenic amines in the regulation of dorsal blood vessel pulse rate in an aquatic oligochaete, Lumbriculus variegatus (Müller, 1774). Bath application of octopamine to intact worms resulted in an acceleration of pulse rate, but not when co-applied with the adenylyl cyclase inhibitor MDL-12,330a. The phosphodiesterase inhibitor theophylline mimicked the effects of OA, but the polar adenosine receptor antagonist 8(p-sulphophenyl)theophylline was significantly less potent than theophylline. Pharmacologically blocking synaptic reuptake of the biogenic amines using the selective 5-HT reuptake blocker fluoxetine or various tricyclic antidepressants also accelerated heart rate. Depletion of the biogenic amines by treatment with the monoamine vesicular transporter blocker reserpine dramatically depressed pulse rate. Pulse rate was partially restored in amine-depleted worms after treatment with octopamine or dopamine, but fully restored following treatment with serotonin. This effect of 5-HT was weakly mimicked by 5-methoxytryptamine, but not by alpha-methylserotonin; it was completely blocked by clozapine and partially blocked by cyproheptadine. Because they are known to orchestrate a variety of adaptive behaviors in invertebrates, the biogenic amines may coordinate blood flow with behavioral state in L.variegatus.

The Drosophila wing hearts consist of syncytial muscle cells that resemble adult somatic muscles

In Drosophila, hemolymph circulation in the wings is accomplished by a pair of wing hearts located in the thorax. The embryonic progenitors of these organs were only recently discovered and found to belong to the cardiac mesoderm. In this study, the functional morphology and the structure of mature organs were studied by light and electron microscopy to characterize the tissues arising from this new set of progenitors. Each wing heart consists of 7-8 muscle cells providing the pumping force, a thin layer of non-contractile mononucleated cells separating the muscle cells from the body cavity, and acellular suspending strands opposing the muscle contractions. The muscle cells are multinucleated syncytia attached to the cuticle via epidermal tendon cells. They have central nuclei and sarcomeres with discontinuous Z-discs, A-bands, and I-bands, whereas H-bands and M-bands are indiscernible. From 9 to 11 actin filaments surround each myosin filament. Mitochondria are abundantly interspersed between myofibrils and accumulated in characteristic outpockets of the plasma membrane. The analysis revealed that the wing heart muscles resemble in their ultrastructure and their mode of attachment adult somatic muscles. This suggests that, despite their origin in the cardiac mesoderm, wing heart progenitors are functionally related to somatic adult muscle precursors.

Influence of PCPA and MDMA (ecstasy) on physiology, development and behavior in Drosophila melanogaster

The effects of para-chlorophenylalanine (PCPA) and 3,4 methylenedioxy-methamphetamine (MDMA, 'ecstasy') were investigated in relation to development, behavior and physiology in larval Drosophila. PCPA blocks the synthesis of serotonin (5-HT) and MDMA is known to deplete 5-HT in mammalian neurons; thus these studies were conducted primarily to target the serotonergic system. Treatment with PCPA and MDMA delayed time to pupation and eclosion. The developmental rate was investigated with a survival analysis statistical approach that is unique for Drosophila studies. Locomotion and eating were reduced in animals exposed to MDMA or PCPA. Sensitivity to exogenously applied 5-HT on an evoked sensory-central nervous system (CNS)-motor circuit showed that the CNS is sensitive to 5-HT but that when depleted of 5-HT by PCPA a decreased sensitivity occurred. A diet with MDMA produced an enhanced response to exogenous 5-HT on the central circuit. Larvae eating MDMA from the first to third instar did not show a reduction in 5-HT within the CNS; however, eating PCPA reduced 5-HT as well as dopamine content as measured by high performance liquid chromatography from larval brains. As the heart serves as a good bioindex of 5-HT exposure, it was used in larvae fed PCPA and MDMA but no significant effects occurred with exogenous 5-HT. In summary, the action of these pharmacological compounds altered larval behaviors and development. PCPA treatment changed the sensitivity in the CNS to 5-HT, suggesting that 5-HT receptor regulation is modulated by neural activity of the serotonergic neurons. The actions of acute MDMA exposure suggest a 5-HT agonist action or possible dumping of 5-HT from neurons.

Compartmentalization of neuronal and peripheral serotonin synthesis in Drosophila melanogaster

In Drosophila, one enzyme (Drosophila tryptophan-phenylalanine hydroxylase, DTPHu) hydroxylates both tryptophan to yield 5-hydroxytryptophan, the first step in serotonin synthesis, and phenylalanine, to generate tyrosine. Analysis of the sequenced Drosophila genome identified an additional enzyme with extensive homology to mammalian tryptophan hydroxylase (TPH), which we have termed DTRHn. We have shown that DTRHn can hydroxylate tryptophan in vitro but displays differential activity relative to DTPHu when using tryptophan as a substrate. Recent studies in mice identified the presence of two TPH genes, Tph1 and Tph2, from distinct genetic loci. Tph1 represents the non-neuronal TPH gene, and Tph2 is expressed exclusively in the brain. In this article, we show that DTRHn is neuronal in expression and function and thus represents the Drosophila homologue of Tph2. Using a DTRHn-null mutation, we show that diminished neuronal serotonin affects locomotor, olfactory and feeding behaviors, as well as heart rate. We also show that DTPHu functions in vivo as a phenylalanine hydroxylase in addition to its role as the peripheral TPH in Drosophila, and is critical for non-neuronal developmental events.