Fly Anoxia

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Abstract

A common insect belonging to the genus Drosophila displays an ability to survive anoxia, a cause for much biomedical interest. Because they are tiny ectotherms, the metabolic rate of Drosophila melanogaster is directly proportional to the temperature of its environment. As such, lowered metabolic rates directly correlate with a decrease in temperature, a positive relationship established by Q10 values. Anoxic conditions also trigger a decrease in metabolic rate in Drosophila melanogaster, which enters a quiescent state when submerged under water. We explored the role of temperature in affecting failure times and recovery of drosophila in anoxia. Drosophila melanogaster submerged in cold water experienced both a lowered Q10 as well as a physiologic response to complete oxygen deprivation; the combined factors resulted in a rapid entry into quiescence, as well as a fast recovery time upon retrieval from these conditions. In contrast, Drosophila melanogaster submerged in warm water took longer to fail and longer to recover. The Drosophila melanogaster used in our experiment were relatively young, aged between ten to eleven days old, a constant variable in the experiment. Our results suggest that cold temperature and anoxic tolerance mechanisms have an additive effect on Drosophila melanogaster’s physiological responses to said adverse conditions; together, they caused a faster, more uniform failure time as well as a faster recovery time than heat and anoxia. Seeing how the anoxic failure times are higher and more uneven in hot-anoxic conditions and how recovery is slowed and more uniform, we also concluded that heat enhances the effects of anoxia and makes recovery time slower for Drosophila melanogaster. Introduction

Animals have a wide range of responses to anoxic conditions. Although large endothermic vertebrates like humans are highly susceptible to anoxia, dying within minutes of complete oxygen deprivation (including no air in the lungs), other animals are facultative anaerobes which can decrease their metabolic rate to avoid this fate (Gorr, et. al. 2010).

When endotherms like humans or rats reduce pyruvate into lactate by using lactate dehydrogenase, they regain NAD+ from NADH in the process, allowing the molecule to be recycled during glycolysis, which allows them to make 2 net ATP for each molecule of glucose. However, lactate dissociates into the blood under anaerobic conditions, gradually overriding the blood’s buffer systems while lowering the pH. This condition, called lactic acidosis, make fermentation an unsustainable pathway for humans.

Another dangerous aspect of anoxia in vertebrate mammalian endotherms is observable in brain ischemia, wherein a lack of glycogen/ glucose and oxygen in neuronal tissues causes them to oxidize the ubiquitous excitatory neurotransmitter glutamate in lieu of oxygen (Plane, T.W., et al. 2004). The marked increase of glutamate in the extracellular matrix induces neuronal excitotoxicity due to the promotion of several calcium using pathways like the inositol phosphatase pathway, which uses signal molecules (including glutamate) to activate its G protein linked receptor, triggering a series of intracellular signaling events which cause intracellular calcium to bind to calmodulin receptors and activate a diverse array of ATP dependent enzymes (White, B.C., et. al. 2000). These enzymes exacerbate the problem of low energy and create energy shortages in vital mechanisms needed for survival of the neuron; in particular, the ATP driven calcium pumps in the cell membrane, endoplasmic reticulum membrane and mitochondrial membrane stop receiving the requisite amount of inorganic phosphates required to maintain low levels of intracellular calcium, which causes extracellular calcium to leak into the cell and activate even more enzymatic pathways. This effectively creates a positive feedback loop which will deplete the cell’s nonrenewable reserves of ATP, eventually...
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