![]() ![]() 13, 14 Mushroom bodies (MBs), though best known for their function in learning and memory, are also involved in suppressing locomotion, 15 and promoting sleep 16, 17 at least in part through serotonin signaling. Results from the Hendricks and Shaw groups have demonstrated that the rest behavior of Drosophila is independent of the circadian clock, and it exhibits similar characteristics to mammalian sleep behavior. A second process controlling the sleep-wake cycle, also known as homeostatic control of sleep, determines the amount of sleep rather than the timing of sleep. 12 In turn, PDF promotes arousal during the late night/early morning via PDF-responsive neurons that control downstream motor activity. Within these neurons, a molecular clock maintained by the products of key clock genes: period ( per), timeless ( tim), Clock ( Clk), and cycle ( cyc), results in the rhythmic regulation of a neuropeptide, PDF (pigment-dispersing factor). 9– 11 The circadian (~24 hour) clock that maintains the timing of the sleep-wake cycle in Drosophila resides in the lateral neurons (LNs) of the brain. The fruit fly Drosophila melanogaster serves as a useful model to study the sleep-wake cycle since it shares conserved mechanisms with mammals. Though manufacturers claim that caffeine and taurine are safe and beneficial, the interaction between caffeine and taurine has not fully been investigated. 8 Both Red Bull® and Monster® have 1000 mg or 0.4% of taurine in the original 250 ml packages, and the amount triples in Monster XXL®. 6 Reported benefits of taurine include cytoprotection 7 and anti-seizure/epilepsy effects. 4 In addition, taurine, a sulfhydryl amino acid found in many tissues including the CNS and muscles, is involved in osmotic regulation 5 and in modulating the release of other amino acid transmitters at synapses. Caffeine is also known to delay the onset of sleep, shorten stage 3–4 nonrapid eye movement (NREM) sleep and reduce total sleep. The side effects of caffeine include insomnia, nausea, heart palpitations, and even death in rare cases. Monster XXL® has as much as 240 mg of caffeine in a 23.5 oz. The amount of caffeine per serving in energy drinks ranges from 76–80 mg or 0.03% (eg, original Red Bull® or Monster®), equivalent to that in a single cup of coffee, to 280 mg or 0.11% (eg, Cocaine®) in 8.3 oz. (or 0.02%), 3 yet many energy drinks have clearly exceeded that limit for a single serving without any warning label. 2 According to US Food and Drug Administration (FDA) regulations, the maximum caffeine content allowed is 71 mg/12 fl.oz. The lack of regulation of caffeine content that could lead to caffeine intoxication, and its recreational use in combination with alcohol, have become growing concerns (see review by Reissig). 1 Two common ingredients found in energy drinks are caffeine and taurine, both classified as neuromodulators. Unfortunately the frequent consumption of these beverages has been linked to risky behavior among college students. These drinks are intended to keep people awake at work or during leisure activities. ![]() In the last decade, energy drinks such as Red Bull® and Monster® have become cultural icons and are frequently marketed towards and consumed by young adults. This intriguing enhancement of caffeine action by low doses of taurine may account for the presence of both compounds in energy-promoting drinks such as Red Bull® and Monster®. A high taurine:caffeine ratio promotes sleep, while a low ratio of taurine:caffeine inhibits sleep to a greater extent than the equivalent amount of caffeine alone. Flies treated with both caffeine and taurine exhibit two differential effects which depend upon the ratio of taurine to caffeine. Our results show that taurine increases sleep, while caffeine, as previously reported, attenuates sleep. At 0.75%, taurine also increases total sleep by 50%. Treatment with taurine at 0.1% to 1.5% reduces locomotor activity by 28% to 86%, and shifts it from diurnal to nocturnal. We show here that flies receiving a low dose of caffeine (0.01%) increase locomotor activity by 25%, and decrease total sleep by 15%. Taurine is a GABA receptor agonist, which is inhibitory to neuronal firing. It has been shown that caffeine, as the most widely used psychostimulant, can boost arousal through the dopamine pathway in the mushroom bodies of flies. We investigated their effects on sleep-wake control in constant darkness using the fruit fly Drosophila as a model system. Caffeine and taurine are two major neuromodulators present in large quantities in many popular energy drinks.
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