Brain glycogen re-awakened

The mammalian brain contains glycogen, which is located predominantly in astrocytes, but its function is unclear. A principal role for brain glycogen as an energy reserve, analogous to its role in the periphery, had been universally dismissed based on its relatively low concentration, an assumption apparently reinforced by the limited duration that the brain can function in the absence of glucose. However, during insulin-induced hypoglycaemia, where brain glucose availability is limited, glycogen content falls first in areas with the highest metabolic rate, suggesting that glycogen provides fuel to support brain function during pathological hypoglycaemia. General anaesthesia results in elevated brain glycogen suggesting quiescent neurones allow glycogen accumulation, and as long ago as the 1950s it was shown that brain glycogen accumulates during sleep, is mobilized upon waking, and that sleep deprivation results in region-specific decreases in brain glycogen, implying a supportive functional role for brain glycogen in the conscious, awake brain. Interest in brain glycogen has recently been re-awakened by the first continuous in vivo measurements using NMR spectroscopy, by the general acceptance of metabolic coupling between glia and neurones involving intercellular transfer of energy substrate, and by studies supporting a prominent physiological role for brain glycogen as a provider of supplemental energy substrate during periods of increased tissue energy demand, when ambient normoglycaemic glucose is unable to meet immediate energy requirements.     

Glycogen metabolism in the rat retina

It has been reported that glycogen levels in retina vary with retinal vascularization. However, the electrical activity of isolated retina depends on glucose supply, suggesting that it does not contain energetic reserves. We determined glycogen levels and pyruvate and lactate production under various conditions in isolated retina. Ex vivo retinas from light- and dark-adapted rats showed values of 44 +/- 0.3 and 19.5 +/- 0.4 nmol glucosyl residues/mg protein, respectively. The glycogen content of retinas from light-adapted animals was reduced by 50% when they were transferred to darkness. Glycogen levels were low in retinas incubated in glucose-free media and increased in the presence of glucose. The highest glycogen values were found in media containing 20 mm of glucose. A rapid increase in lactate production was observed in the presence of glucose. Surprisingly, glycogen levels were the lowest and lactate production was also very low in the presence of 30 mm glucose. Our results suggest that glycogen can be used as an immediate accessible energy reserve in retina. We speculate on the possibility that gluconeogenesis may play a protective role by removal of lactic acid.     

The use of clove oil to induce anaesthesia,and its effects on blood chemistry,in Lates niloticus from Lake Victoria,Uganda

The efficacy of clove oil as an anaesthetic and its effects on blood parameters in Nile perch Lates niloticus were evaluated in 2010. Clove oil concentrations of 49.3, 73.9 and 98.5?mg l^?1 induced anaesthesia in <3?min, while the average recovery time from anaesthesia was 11?min 22 s. The optimal oil clove oil concentration was 49.3?mg l^?1, inducing anaesthesia in 4?min 33 s, with recovery in 3?min 31 s. No stress response was elicited. Clove oil at a concentration of 24.6?mg l^?1 was an effective sedative, whereas a concentration of 49.3?mg l^?1 was sufficient for measuring fish and stripping gametes. A concentration of 73.9?mg l^?1 induced anaesthesia within 4?min and fish recovered in 10?min. Therefore, clove oil was an effective anaesthetic and sedative for the handling of Nile perch within a mass range of 0.4–12?kg fish^?1.     

Oxygen consumption and energy metabolism of the early mouse embryo

Oxygen consumption of preimplantation and early postimplantation mouse embryos has been measured using a novel noninvasive ultramicrofluorescence technique, based on an oil-soluble, nontoxic quaternary benzoid compound pyrene, whose fluorescence is quenched in the presence of oxygen. Pyruvate and glucose consumption, lactate production, and glycogen formation from glucose were also measured. Preimplantation mouse embryos of the strain CBA/Ca × C57BL/6 were cultured in groups of 10–30 in 2 μl of modified M2 medium containing 1 mmol l⁻¹ glucose, 0 mmol l⁻¹ lactate, and 0.33 mmol l⁻¹ pyruvate, for between 4–6 hr. Day 6.5 and 7.5 embryos were cultured singly in 40 μl M2 medium for between 2–3 hr. Oxygen consumption was detected at all stages of development, including, for the first time, in the early postimplantation embryo. Consumption remained relatively constant from zygote to morula stages before increasing in the blastocyst and day 6.5–7.5 stages. When expressed as QO₂ (μl/mg dry weight/hr), oxygen consumption was relatively constant from the one-cell to morula stages before increasing sharply at the blastocyst stage and declining to preblastocyst levels on days 6.5 and 7.5. Pyruvate was consumed during preimplantation stages, with glucose uptake undetectable until the blastocyst stage. Glucose was the main substrate consumed by the 6.5 and 7.5 day embryo. The proportions of glucose accounted for by lactate appearance were 81%, 86%, and 119% at blastocyst, day 6.5, and day 7.5 stages, respectively. The equivalent figures for glucose incorporated into glycogen were 10.36%, 0.21%, and 0.19%, respectively. The data are consistent with a switch from a metabolism dependent on aerobic respiration during early preimplantation stages to one dependent on both oxidative phosphorylation and aerobic glycolysis at the blastocyst stage, a pattern which is maintained on days 6.5 and 7.5. Our technique for measuring oxygen consumption may have diagnostic potential for selecting viable embryos for transfer following assisted conception techniques in man and domestic animals. © 1996 Wiley-Liss, Inc.     

Primary and secondary stress responses to line capture in the blue mao mao

Primary and secondary stress responses were measured in wild Scorpis violaceus subjected to burst swimming from angling. Fish were blood sampled from 20 s to 30 min after hooking. Consequent rises in plasma adrenaline (14–316 nmol l⁻¹), noradrenaline (25–345 nmol l⁻¹), and cortisol (0.4–197 ng ml⁻¹) correlated with time since capture, and plasma lactate (0.1–12.2 mmol l⁻¹) reflected work done during intense exercise. Haemoglobin concentration and haematocrit also increased with exercise, and erythrocyte swelling occurred. Wild S. violaceus demonstrated a spontaneity and intensity of exercise not seen in fish acclimatized to aquarium conditions. By contrast, the stress responses of fish in captivity, despite careful husbandry, differed qualitatively and quantitatively from those in the wild. Cannulated fish had higher resting plasma cortisol concentrations (61.9±9.5 ng ml⁻¹) than did rapidly caught wild fish (<5 ng ml⁻¹) and these values were not significantly changed with burst swimming. Catecholamine secretion, possibly suppressed by cortisol, was insufficient to cause erythrocyte swelling. Erythrocyte nucleotides do not play a role in exercise, but are elevated in captive fish. It is hypothesized that primary endocrine responses are triggered by higher cortical processing of sensory information which is fundamentally different in the natural environment.     

低氧预处理小鼠脑及血液中糖原与乳酸含量的变化

采用昆明小鼠为实验对象,将实验动物随机分为H4组（重复低氧4次,低氧预适应组）、H1组（只低氧1次,低氧对照组）和H0组（正常对照组,即不低氧组）,分别测定全脑及不同脑区（端脑、间脑、中脑、脑桥、小脑和延髓）糖原、乳酸的含量,同时测定血液中乳酸的含量。结果：H4组全脑糖原含量显著高于H1及H0组,其中H4组端脑、间脑和脑桥内糖原含量显著高于H1组及H0组相应的脑区,H1组全脑糖原含量显著低于H0组,其中H4组端脑、间脑和脑桥内糖原含量显著高于H1组及H0组相应的脑区,H1组全脑糖原含量显著低于H0组,但各个脑区糖原含量的差别无显著意义。H4、H1组全脑乳酸含量无显著差异,但均显著高于H0组,而H4组血液中乳酸的含量则显著低于H1组及H0组。结果提示,在低氧预适应过程中,脑糖原增加与脑乳酸降低同时发生,脑有氧代谢参与低氧预适应或低氧耐受的形成。