Sweet and sour recipes for the brain. 3. Let the neurons breathe!

Brain metabolism,Energy Substrates,Methodology — 2:30 pm

Latest update: Critical State of Energy Metabolism in Brain Slices: The Principal Role of Oxygen Delivery and Energy Substrates in Shaping Neuronal Activity 

Part 2. Energy substrates: too sour?
Part 3. Let the neurons breathe!

In the recent experimental work by Ivanov et al., the authors discuss (among other things) the role of oxygenation in neuronal efficiency. They cite the works showing that in adult animals, both synaptic function and neuronal networking strongly depend on the level of oxygenation in brain slices. They further registered the oxygenation levels at various speed of brain slice’s perfusion with artificial cerebrospinal fluid (ACSF, read more about it – > here) in very young animals. They showed that in a standard camera (importantly: as opposite to the interface cameras) at an upper-standard perfusion rate of 3.25 ml/min oxygen content is only 50% of that showed in their experiments with the flow rate of 9 ml/min, and that’s on the slice’s surface. Deeper into the slice’s tissue, oxygenation rapidly decreased and in the middle of a 400 micron-thick slice, oxygen is completely absent. A decrease in the perfusion rate from 15 ml/min to 3.25 ml/min resulted in an about two-fold reduction of the amplitude of so called local field potential (a measure of synaptic robustness). They concluded: “Therefore, as in more mature neurons (Schurr and Payne, 2007; Hajos et al., 2009; Garcia et al., 2010), the synaptic function of neonatal neurons during network activity profoundly depends on oxidative metabolism.”

Interestingly, the authors who failed reproducing some of the effects of energy substrates shown by the group of Y. Zilberter in 2009-2011 used the experimental design corresponding to a severe lack of oxygen in slices.

Thus, Tyzio et al., 2011, in their imaging experiments worked with neuronal populations occupying in slices deeper areas than those in which oxygen can be supplied at the used perfusion rate 2–3 ml/min. Same is true for the work of Ruusuvuori et al., 2010 since they registered GDPs that also involves neuronal populations larger than the oxygenation areas in the slices.

This is an important difference in experimental techniques used by the above mentioned authors on one hand and: Rheims et al., 2009, Holmgren et al., 2010, Mukhtarov et al., 2011, Ivanov et al., 2011 on the other hand – where the perfusion rates of 9 to 15 ml/min were used.

This alone can explain the difference in effects of one of the ketone bodies observed by Holmgren et. al., 2010 and Tyzio et al., 2011. The matter is, for BHB to act, oxygen availability is mandatory while glucose can work in anaerobic condition although in this case, it yields much less energy: 2 molecules of ATP for each molecule of glucose comparing with 32 molecules of ATP for each molecule of glucose in aerobic conditions (Lehninger, 2005). No wonder anaerobic glycolysis, especially in very young animals, fails supporting normal neuronal activity. A vicious circle may occur: lack of energy -> neuronal hyperactivity -> increased energy demand -> increased energy deficit, etc.

References

  1. Garcia, A.J., 3rd, Putnam, R.W., and Dean, J.B. (2010). Hyperbaric hyperoxia and normobaric reoxygenation increase excitability and activate oxygen-induced potentiation in CA1 hippocampal neurons. J Appl Physiol 109, 804-819.
  2. Hajos, N., Ellender, T.J., Zemankovics, R., Mann, E.O., Exley, R., Cragg, S.J., Freund, T.F., and Paulsen, O. (2009). Maintaining network activity in submerged hippocampal slices: importance of oxygen supply. Eur J Neurosci 29, 319-327.
  3. Holmgren CD, Mukhtarov M, Malkov AE, Popova IY, Bregestovski P, Zilberter Y (2010) Energy substrate availability as a determinant of neuronal resting potential,GABAsignaling and spontaneous network activity in the neonatal cortex in vitro. J Neurochem 112:900 –912.
  4. Ivanov A, Mukhtarov M, Bregestovski P and Zilberter Y (2011). Lactate effectively covers energy demands during neuronal network activity in neonatal hippocampal slices. Front. Neuroenerg. 3:2.
  5. Khakhalin A (May 18, 2011). Questioning the depolarizing effects of GABA during early brain development. <a style=”color: #cc0000;” title=”Questioning the depolarizing effects of GABA during early brain development” href=”http://jn.physiology.org/content/early/2011/05/13/jn.00293.2011.abstract” target=”_blank”>J Neurophysiol doi:10.1152/jn.00293.2011</a>.</p>
  6. Ruusuvuori E, Kirilkin I, Pandya N, Kaila K. Spontaneous Network Events Driven by Depolarizing GABA Action in Neonatal Hippocampal Slices are Not Attributable to Deficient Mitochondrial Energy Metabolism. J Neurosci. 2010 Nov 17;30(46)
  7. Lehninger, A.L. (2005). “Oxydative phosphorylation and photophosphorylation,” in Principles of biochemistry, eds. D.L. Nelson &amp; M.M. Cox. Forth ed: W. H. Freeman), 690-740.
  8. Schurr, A., and Payne, R.S. (2007). Lactate, not pyruvate, is neuronal aerobic glycolysis end product: an in vitro electrophysiological study. Neuroscience 147, 613-619.
  9. Tyzio, R., Allene, C., Nardou, R., Picardo, M.A., Yamamoto, S., Sivakumaran, S., Caiati, M.D., Rheims, S., Minlebaev, M., Milh, M., Ferre, P., Khazipov, R., Romette, J.L., Lorquin, J., Cossart, R., Khalilov, I., Nehlig, A., Cherubini, E., and Ben-Ari, Y. (2011). Depolarizing actions of GABA in immature neurons depend neither on ketone bodies nor on pyruvate. J Neurosci 31, 34-45.

The basics of ketogenic diet: works of Shaffer and Wilder & Winter

Glucose,Ketogenic diet,Ketone bodies,Ketosis, ketogenesis,Methodology — Tags: , — 6:16 am

It is interesting that while the ketogenic diet becomes well researched as a method for improving energy metabolism during quite a few medical conditions and the number of original research articles as well as reviews grow currently approaching 15,000, only 19 out of all of them cite the original work, which in fact is the basis of the diet. >>> Read more

The ketogenic diet is no longer considered a strictly anti-epileptic diet: its suggested and tested applications includes a broad spectrum of disorders of energy metabolism. The ketogenic ratio formula used in clinics for calculating the ketogenic diet composition was offered by Wilder and Winter in 1922 (1). They argued that the levels of ketogenic substances depend on the ratio between fatty acids and glucose of the metabolizing foods. The ratio when ketogenesis is initiated they called the threshold of ketogenesis: “When the proportion of acetoacetic acid to glucose in such mixtures was that of 1 (or possibly 2) molecules of acetoacetic acid to 1 of glucose, the former substance was completely oxidized. When the proportion of glucose was less, a considerable fraction of acetoacetic acid escaped oxidation.”

Shaffer (2, 3) calculated the number of molecules of ketogenic substrates corresponding to the number of molecules of glucose and concluded that the maximal ratio compatible with the oxidation of the ketogeniec compounds was reached when a ratio of of ketogenic molecules to the number of glucose molecules was 1: 1. He subsequently considered that each glucose molecule is ketolytic for 2 molecules of acetoacetic acid, a 2:l ratio.

Wilder and Winter, 1922 included in their formula the following measurements obtained in clinical settings:

1) basal metabolism for 24 hour periods plus 10 per cent for the specific dynamic action of food and 10 per cent for movements;

2) the calories from the protein metabolism assessed by nitrogen excretion;

3) the calories from fat metabolism taken as the sum of the calories of protein and carbohydrate combined subtracted from the total calories of the day.

The values for carbohydrate and fat are used in the calculation of the ratio between the ketogenic molecules and the glucose molecules (2, 3).

“Under the conditions of these experiments, provided these assumptions are tenable, the ratio between the ketogenic and the glucose molecules at which a clinically significant ketosis appears has a value of at least 2: 1. A ratio of this value implies that every molecule of glucose is ketolytic for 2 molecules of acetoacetic acid.”

References

  1. Wilder R., Winter M. Thew threshold of ketogenesis. J. Biol. Chem. 1922 52: 393-401.
  2. Shaffer, P. A., Antiketogenesis. I. An in vitro analogy, J. Biol.Chem., 1921, xlvii, 433.
  3. Shaffer, P. A., Antiketogenesis. II. The ketogenic antiketogenic balance in man, J. Biol. Chem., 1921, xlvii, 449.

 

 

 

Alzheimer’s disease and a long-standing exposure to glucose in the Western diet

Alzheimer's,Glucose,Ketone bodies,Lactate — 6:35 am

 

Chronic exposure to glucose due to the traditional Western diet impairs neuronal function and causes apoptosis (programmed neuronal death), concluded Drs Seneff & Wainwright (UK) and Mascitelli (Italy). Their reasoning was roughly the following:

The amyloid-beta peptide (AB) in Alzheimer’s disease (AD) plaques so far seen as a hallmark of this disease, in fact may be an early attempt of protection from its development.  AB switches neuronal metabolism from glycolysis-based to the use of other substrates, e.g., lactate and ketone bodies. This is a very important adjustment in the AD case since there’s an insulin resistance in the AD brain indicating an inadequate ability to utilize glucose. Moreover, the levels of advanced glycation end-products (harmful in any case) are increased in AD. The damage they induce interferes with delivery of fats and cholesterol to astrocytes, and consequently to neurons. This is important because for smooth communication between neurons, sufficient levels of fat and cholesterol is required and the AD CSF is deficient in both. Synthesis of AB is increased when lipid supply is deficient. In the condition of this deficiency, there’s an increase in synthesis of excitatory neurotransmitter glutamate leading to oxidative damage and toxic overexcitability.

The good news is, wrote the authors, a simple dietary change towards lower carbohydrate intake and higher fats intake, may be efficiently protective against AD.

Source:

European Journal of Internal Medicine 22 (2011) 134–140

Toxic glycolysis and brain aging

Glucose,Hormesis,Theories — Tags: , , , , , , — 8:29 am

Related article: Prescription-strength stress as a medicine

The intermittent glycolysis during fasting, physical exercise, and stress may delay senescence by lowering intracellular concentration of methylglyoxal, a common intermediate in the Maillard reaction (glycation).

A simple logic allows to imagine that a situation when food is available to an animal at all times and in any quantities should be very seldom. In real life, there are seasons when food is abundant and seasons when it’s scarce. To smoothen the energy delivery to vital organs, there all kind of depots, most famous (or rather infamous for us human beings in Western societies) is the fat depot, having practically unlimited capacity. There is clinical evidence that a human body can save in this depot enough energy to feed itself for a year. Vitamins and electrolyte fluids should be adequately supplied of course, but no calories enter the body – and it survives!

The opposite situation, when animals are allowed to eat as much as they can, as often as they can, is called ad libitum (AL). In experiments on beneficial effects of calorie restriction (CR), the food intake in the AL situation is taken for 100% and then different percentages of restrictions are applied to see CR effectiveness to slow down the process of aging, especially brain aging.

In an early study of the energy metabolism McCarter and Palmer (1) interesting differences were revealed, between rats fed CR diets and those fed the same food but AL. Although in both groups energy metabolism was mostly glycolytic, taping in carbohydrate metabolic way, CR very soon after feeding switched to using their bodies’ fat reserves with their glycolysis suppressed, while the AL group maintained practically non-stop glycolysis.

So it’s been suggested that that the beneficial effects of CR could be due to suppression of glycolysis and in experiments of Walker et al. (2) and Partridge and Brand (3) the question of whether the shortened life-span of AL animals results from some metabolic toxicity, specifically whether glycolysis is deleterious but possibly hormetic (4)

The hormesis hypotheses by Masoro (5) and Sinclair (6) suggests that intermittent stress may induce synthesis of long-term protective functions. Glycolytic intermediates dihydroxyacetone- and glyceraldehyde-3-phosphates are form methylglyoxal (MG), which is potentially toxic.

Hipkiss (7) suggested that non-stop glycolysis is deleterious due to the generation of MG, but periods of glycolysis interruption could be hormetic. MG damages mitochondria and induces a pro-oxidant state characteristics to cellular aging. The decreased glycolysis during CR may delay senescence by lowering intracellular MG concentration compared to AL animals.

Sources

1. Am. J. Physiol. 1992 263, E448-E452

2. Mech. Ageing Dev. 2005 126, 929-937

3. Mech. Ageing Dev. 2005 126, 911-912

4. Hormesis – An effect in which a toxic substance acts like a stimulant in small doses, but it is an inhibitor in large doses.

5. Mech. Ageing Dev. 2005 126, 913-922

6. Mech. Ageing Dev. 2005 126, 987-1002.

7. Mech. Ageing Dev. 2006 127 8-15

Glucose versus lactate in immature brain slices

Brain metabolism,Energy Substrates,Ethics in science,Excitatory GABA,Lactate,Methodology,Neurodegenerative diseases,Neuroscience FAQ, Q&A — Tags: — 11:55 am

Related Q&A: “Y Ben-Ari writes that ‘Zilberter and Bregestovski and colleagues’ dealt with ‘ketone body metabolites’. What does ketone body metabolite mean? ”

About this post

1. These quotes were first used by Elly Strammer at F1000.com. After she agreed to remove her post from there, she contacted us suggesting that we use the quotes. We thank Elly for her contribution and for further commenting at the Naturally Selected

2. We received many questions regarding this post, quite a few of them concerned the formatting, which was not helping to clearly understand the issue. Because of that, we updated the post making sure to visually indicate quotes belonging to the arguing sides (according to F1000.com) . Now, remarks related to comments concerning the works of Y. Zilberter et al. are marked as  and remarks by Y. Ben-Ari are marked as 

 ”We demonstrate that in the neonatal brain, Em [membrane potential] and EGABA [reversal potential of GABA-induced anionic currents] strongly depend on composition of the energy substrate pool. Complementing glucose with ketone bodies, pyruvate or lactate resulted in a significant hyperpolarization of both Em and EGABA, and induced a radical shift in the mode of GABAergic synaptic transmission towards network inhibition.” (1)

“The main conclusions of our work are that the inhibitory effect of L-lactate on GDPs is not mediated by mitochondrial energy metabolism, and that glucose at its standard 10 mM concentration is an adequate energy substrate for neonatal neurons in vitro.” (2)

 ”We show that in the presence of glucose, lactate is effectively utilized as an energy substrate, causing an augmentation of oxidative metabolism. Moreover, in the absence of glucose lactate is fully capable of maintaining synaptic function. Therefore, during network activity in neonatal slices, lactate can be an efficient energy substrate capable of sustaining and enhancing aerobic energy metabolism.” (3)

“Lactate is not an efficient replacement for glucose and, as in vivo glucose is always kept at 4-5mM in the brain even in conditions of severe stress.” (4 a)

“The fact is, in the extracellular fluid (ECF) in the brain, glucose concentration is between 1.9 mM and 0.59 while lactate concentration is between 5.1 mM and 0.78 mM (for review, see [9 in this post]). The question arises: why 10 mM glucose in standard ACSF is adequate but 10 mM lactate is not.” (5)

“Clearly, the suggestions of Zilberter and colleagues rely on wrong assumptions and results that have not been reproduced.” (4 a)

“The effect of weak acids on GABA reversal potential and GDP generation was initially described for 4-5 mM concentrations of BHB [ketone body beta-hydroxybutyrate] (Rheims et al. 2009 ), lactate and pyruvate (Holmgren et al. 2010), and was later confirmed by independent research groups for similar concentrations of pyruvate (Tyzio et al. 2011), lactate and propionate (Ruusuvuori et al. 2010).” (6)

“From a clinical perspective, it is interesting to stress that relying on their observations on the positive actions of lactate on metabolism, Zilberter and colleagues have suggested that administration of lactate may be “a novel therapeutic tool to cure Parkinson, Alzheimer, Leigh syndrome and epilepsies” (4a)

 From Brain Fuels: This quotation is taken out of context. The exact piece from (9) reads: “… a growing body of evidence shows that metabolic stress caused by impaired energy homeostasis is a common feature of neurodegenerative disorders (NDDs) such as Alzheimer disease, Leigh syndrome, epilepsy, dementia, multiple sclerosis, neuropathies or ataxias [88] and [89]. We speculate that endogenous ES such as lactate, BHB and pyruvate or their combinations can be efficient in treatingNDD, and would address the cause rather than symptoms. Indeed, the neuroprotective effects of pyruvate have been repeatedly demonstrated in cases of brain ischemia, hypoglycemia, hemorragia, stroke and kainate-inducedepileptic brain damage[90], [91], [92]and [93]. Further research into mechanisms of the effects of ES on fundamental neuronal properties might allow more rapid progress in preventing and managing NDDs.”

The comment made on 29 Jul 2011 (4 b) quoted this paragraph with the references removed thus attributing the text solely to (9).

“Considering the compelling and well-known clinical observation that high lactate level is a classical sign of neuron suffering and severe conditions that require rapid intervention, this suggestion is, to say the least, astonishing.” (4 a)

“The bulk of the evidence suggests that lactate is an important intermediary in numerous metabolic processes, a particularly mobile fuel for aerobic metabolism, and perhaps a mediator of redox state among various compartments both within and between cells. Lactate can no longer be considered the usual suspect for metabolic ‘crimes’, but is instead a central player in cellular, regional and whole body metabolism… we might term the period from the 1930s to approximately the early 1970s the dead-end waste product era.” (7)

” It is curious that Dr Zilberter and colleagues refer to metabolism but have never reported measuring it.” (4 b)

“…Ivanov et al. (2011) simultaneously recorded oxygen tension, NAD(P)H fluorescence transients and local field potentials during electrical stimulation of the hippocampal Schaffer collateral pathway in neonatal brain tissue slices from mice. From the very beginning, the authors took great care to ensure both viability and functionality of their preparations. They convincingly demonstrated that surprisingly high superfusion rates with standard artificial cerebrospinal fluid (ACSF) in the slice chamber are required to ensure adequate oxygenation and complete electrical function in blood-free tissue slices. An important implication of this methodological tour de force is that under many previously reported experiments the requirements for viability may been met while the functionality may have been compromised.” (8)

References

  1. Holmgren, C. D., Mukhtarov, M., Malkov, A. E., Popova, I. Y., Bregestovski, P., and Zilberter, Y. (2010). Energy substrate availability as a determinant of neuronal resting potential, GABA signaling and spontaneous network activity in the neonatal cortex in vitro. J. Neurochem. 112, 900–912.
  2. Ruusuvuori E et al. (2010). Spontaneous network events driven by depolarizing GABA action in neonatal hippocampal slices are not attributable to deficient mitochondrial energy metabolism. J Neurosci. Nov 17; 30(46):15638-42
  3. Ivanov A, Mukhtarov M, Bregestovski P and Zilberter Y (2011) Lactate effectively covers energy demands during neuronal network activity in neonatal hippocampal slices. Front. Neuroenerg. 3:2.
  4. Ben-Ari Y.  a) Faculty of 1000, 06 Jan 2011, evaluation,  b) 29 Jul 2011, comment.
  5. Zilberter Y. Faculty of 1000, 19 May 2011 and July 14 2011, comments.
  6. Khakhalin A (May 18, 2011). Questioning the depolarizing effects of GABA during early brain development. J Neurophysiol doi: 0.1152/jn.00293.2011.
  7. Mendel I. Faculty of 1000, 04 Jun 2011, comment (Currently the comment is removed).
  8. Kasischke K (2011) Lactate fuels the neonatal brain. Front. Neuroenerg. 3:4. doi: 10.3389/fnene.2011.00004
  9. Zilberter Y, Zilberter T, Bregestovski P. (2010) Neuronal activity in vitro and the in vivo reality: the role of energy homeostasis. Trends PharmacolSci 31:394–401.

What can be done to fight off Alzheimer’s disease?

Alzheimer's,Neuroscience FAQ, Q&A,Parkinson's,Pyruvate — 12:41 pm

Q&A and FAQ (archived) :: Ongoing Q&A :: Neuroscience Q&A and FAQ

Question
I’ve read on WebMD that there’s no evidence that anything can be done to fight off Alzheimer’s disease. But I also read the opposite opinions. What is yours? – Donna

Answer
Dear Donna,

You probably mean the following conclusion cited by WebMD:

“There is currently no evidence considered to be of even moderate scientific quality supporting the association of any modifiable factor (nutritional supplements, herbal preparations, dietary factors, prescription or nonprescription drugs, social or economic factors, medical conditions, toxins, environmental exposures) with reduced risk of Alzheimer’s disease,” concludes the report, issued by a National Institutes of Health consensus panel on Alzheimer’s prevention.”

I am surprised that they haven’t mentioned exercise, for which, in my humble opinion, a solid body of evidence exists and the caffein research, for which intricate mechanisms are being researched. Also, quite a few harmful influences such as hydrogen peroxide, glutamate, zinc, and copper/cysteine were convincingly reported. I added caffein effects on another neurodegenerative disease, the Parkinson’s but I know of similar studies in Alzheimer’s.

Walking away from dementia

Coffee, tea, and chocolate can help to avoid Parkinson’s disease

Pyruvate protects neurons against A-beta peptides characteristic for Alzheimer’s
Tanya Zilberter

F1000 and the lactate controversy

Ethics in science,Ketosis, ketogenesis,Lactate,Neuroscience FAQ, Q&A — Tags: — 9:11 am

Q&A and FAQ (archived) :: Ongoing Q&A :: Neuroscience Q&A and FAQ

Question: Hi Tanya,

I am fascinated by development at the Faculty of 1000 started by Y. Ben-Ari. I couldn’t contain myself and posted a comment there. However, I felt a little out of place being just a student arguing with a real scientist. So I still have a couple of questions to ask you.

1. Y Ben-Ari writes there that “Zilberter and Bregestovski and colleagues” dealt with “ketone body metabolites”. What does ketone body metabolite mean? From the articles (Rheims et al., 2009; Holmgren et al., 2010) Y. Ben-Ari refers, I could only find beta-hydroxybutyrate and basing on my textbook, I thought that ketone bodies are metabolized in the brain resulting in CO2, HCO3- and acetone.”]

2. Y Ben-ari argues with your statement and here’s his exact words: “Zilberter and colleagues have suggested that administration of lactate may be “a novel therapeutic tool to cure Parkinson, Alzheimer, Leigh syndrome and epilepsies”. What did you mean the “tool to cure”?

Thank you!

Ingrid

Answer: Hi Ingrid,

The phrase “ketone body metabolites” is used very scarcely and I’ll give you exact usage of it, then I’ll explain what you probably know already from your textbook.

From those authors who use this phrase, most of them refer to the work of Miles et al. (1), the accurate quote of which is: “ketone body metabolites (CO2, bicarbonate and acetone)” (1). Fontain et al. (2) mention ketone bodies metabolites listing them as beta-hydroxybutyric acid and acetoacetic acid, which is not exactly accurate since they both are ketone bodies themselves.

Other than that, the phrase has a different meaning, like this: “Fatty acids and their ketone body metabolites may serve as afferent signals to modulate food intake” (3). Clearly, ketone bodies are meant as metabolites of fatty acids, again a textbook information.

A citation from very recent reference (4): “Ketone bodies, as described here, comprise acetoacetic acid (AcAc), D-3-hydroxy-n-butyric acid (3HB), and acetone.” Note that they are ketone bodies, not ketone body metabolites.

Now, from the textbook (5): In muscle and brain, ketone bodies yield ATP + CO2 (p. 905); Acetoacetate  + H2O -> Acetone + HCO3- (p. 920)

None of the the two articles Y Ben-Ari refers to in his evaluation concerns anything other than beta-hydroxybutyrate, not other ketone bodies, not ATP, CO2 or HCO3-, or acetone.

As to your question number 2, text concerning “therapeutic” might be from (6): “Our hypothesis predicts that the adequate delivery of energy substrates may interrupt this pathological spiral of events and provide therapeutic options targeting the cause of pathologies rather than their symptoms”. However, there’s nothing wrong with this statement  even as it’s cited (excluding of course the words “cure”, which I can hardly imaging being in the Zilberter and coauthors’ vocabulary) and many authors describe and discuss metabolic crisis in connection with neurodegenerative diseases.

1. Miles J et al., (1980) Determination of 14C radioactivity in ketone bodies: a new, simplified method and its validation. J Lipid Res, 21, 646-650.

2. Fontaine M et al. (1996) Acylcarnitine removal in a patient with acyl-CoA beta-oxidation deficiency disorder: effect of L-carnitine therapy and starvation Clinica Chimica Acta 252; 109-122

3. Bray GA “A Guide to Obesity and the Metabolic Syndrome: Origins and Treatment” CRC Press, 2011.

4. Sass JO (2011). Inborn errors of ketogenesis and ketone body utilization. J Inherit Metab Dis DOI 10.1007/s10545-011-9324-6

5. Lehninger, A. L. (2005). in Principles of Biochemistry, 4th Edn, eds D. L. Nelson and M. M. Cox (W. H. Freeman),

690–740.

6. Holmgren, C. D., Mukhtarov, M., Malkov, A. E., Popova, I. Y., , P., and Zilberter, Y. 2010). Energy substrate availability as a determinant of neuronal resting potential, GABA signaling and spontaneous network activity n the neonatal cortex in vitro. J. Neurochem. 112, 900–912.

Sweet and sour recipes for the brain 4. “Physiological” concentrations: what and where?

Excitatory GABA,Ketone bodies,Lactate,Methodology,Pyruvate — 6:27 am

Part 2. Energy substrates: too sour?
Part 3. Let the neurons breathe!

What concentrations are physiological and what are not (usually called pharmacological)? The physiological ones  normally refer to the levels of a substance relevant to the naturally occurring, which, logically, for neurons is the milieu they strive in. It is called extracellular fluid (ECF) and is notorious for dramatic differences with not only blood (plasma) but even with the cerebrospinal fluid (CSF).

“Importantly, microdialysis data have shown that both in adult humans and in rats,the basal glucose levels are about 1–2 mM in the ECF of the neocortex and hippocampus [32,33,37,38] compared with 5–7 mM in the blood, whereas concentrations of lactate are about 2–5 mM in the ECF [32,34,39,40] compared with 1–2 mM in the adult blood.” (Zilberter et al., 2010). The authors further stressed the imperative of providing adequate means for energy substrates to be utilized in the artificial milieu, in which brain slices are placed:

“In brain slices, energy deficiency cannot be managed in the same way as in whole-body homeostasis, resulting in higher ES levels in  slices than in vivo. The importance of a proper oxygen supply should be stressed [55], because oxidative phosphorylation is proportional to the presence of O2. Therefore, at an inadequate oxygen level, the efficacy of ES might be negligible. It is not surprising that energy metabolism in slices differs from that occurring in the living brain, and is probably impaired [52–54].”

Khakhalin (2011) wrote in his recent review that effects of ES on GABA action has been shown for “…4-5  mM concentrations of beta-hydroxybutyrate  (Rheims et al. 2009), lactate and pyruvate (Holmgren et al. 2010), and was later confirmed by independent research groups for similar concentrations of pyruvate (Tyzio et al. 2011), and lactate (Ruusuvuori et al. 2010).” He continued arguing whether  the concentrations were  ”physiological ” in the experiments showing equal results in different authors who made, however, different conclusions: Tyzio et al. state that the physiological concentration of pyruvate is 1.6 – the one they measured in plasma.

“This comparison may be not valid, however, as it is well known from microdialysis studies that the extracellular fluid, immediately surrounding neural cells, differs in its composition not only from the blood plasma, but even from the cerebrospinal fluid. In particular, concentration of lactate in the extracellular fluid of rats and humans was found to be 2-5 times higher than in the blood plasma… 4-5 mM concentrations are likely to be physiologically relevant… On the other hand, at these concentrations both lactate and pyruvate induce noticeable changes in GABA- and glutamatergic transmission in developing neural networks. It means that some changes in experimental protocols and related theoretical paradigms may still be necessary.”

Kasischke (2011) in his comment on the article by Ivanov et al., 2011, wrote: “From the very beginning, the authors took great care to ensure both viability and functionality of their preparations.”

“An important implication of this methodological tour de force is that under many previously reported experiments the requirements for viability may been met while the functionality may have been compromised.”

References

 

  1. Zilberter Y, Zilberter T, Bregestovski P. (2010) Neuronal activity in vitro and the in vivo reality: the role of energy homeostasis. Trends Pharmacol Sci., 31(9):394-401
  2. [32,33,3437,38,39,40,52-55]  are cited in Zilberter et al. (2010)
  3. Khakhalin A (May 18, 2011). Questioning the depolarizing effects of GABA during early brain development. J Neurophysiol doi: 0.1152/jn.00293.2011.
  4. Tyzio et al. (2011) and  Ruusuvuori et al. (2010) are cited in Khakhalin ( 2011).
  5. Kasischke K (2011). Lactate fuels the neonatal brain. Frontiers in Neuroenergetics; 3, 4

“Brain metabolism in vitro” and those sour energy substrates

Brain metabolism,Energy Substrates,Excitatory GABA,Glucose,Ketone bodies,Lactate,Pyruvate — Tags: , — 10:31 am

Part 2. Energy substrates: too sour?
Part 3. Let the neurons breathe!
This paper suggests that the developmental switch in the reversal potential for gamma-aminobutyric acid (GABA) is regulated by different energy sources

This paper suggests that the developmental switch in the reversal potential for gamma-aminobutyric acid (GABA) is regulated by different energy sources

An evaluation of our article (1) appeared in the “Faculty of 1000 postpublication peer reviews” the conclusion being:

The findings of Rheims et al. have a potentially major impact on our understanding of GABAergic function during development, bringing back an element of inhibition in developing neuronal networks that appeared to rely entirely on excitatory connections (2).

This article (1) along with the article (3) later became an indirect subject of another evaluation (4) although formally, the evaluation concerned a different paper (5), which has been commended because (the author’s words):

“It settles an important issue related to brain metabolism in vitro and the role of acidification in brain patterns.”

The acidification issue doesn’t seem to be resolved either in 5 nor in 4, so a comment to the evaluation appeared in May 2011,  stating among other things the following:

We showed that inhibition of spontaneous network activity in neonatal hippocampal slices by energy substrates is not correlated with intracellular acidification (7) and that they work altering intrinsic features of energy metabolism namely NAD(P)H and oxygen utilization (8).

Another data challenged in 5 is whether lactate as efficient as an energy substrate: “Lactate is not an efficient replacement for glucose” wrote Dr Ben-Ari and Y. Zilberter in his comment referred to the paper 8 titled “Lactate effectively covers energy demands during neuronal network activity in neonatal hippocampal slices” and the work of Wyss et al. (9) titled “In Vivo Evidence for Lactate as a Neuronal Energy Source”.

References

1. Rheims S, Holmgren CD, Chazal G, Mulder J, Harkany T, Zilberter T, Zilberter Y. (2009) J Neurochem.  Aug;110(4):1330-8. Epub 2009 Jun 22. (on Brain Fuels)

2. Scimemi A, Diamond J: 2009. F1000.com/1166168

3. Holmgren CD, Mukhtarov M, Malkov AE, Popova IY, Bregestovski P, Zilberter Y. (2010) J Neurochem. Feb;112(4):900-12. Epub 2009 Nov 24. (on Brain Fuels)

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The metabolic rate of plasma-borne lactate is a function of brain lactate concentration

Astrocyte–neuron lactate shuttle,Lactate — Tags: , — 5:07 am

In the Journal club section of the Journal of Neuroscience (written exclusively by graduate students or postdoctoral fellows), a review by C. Figley from Johns Hopkins University and Kennedy Krieger Institute, Baltimore, Maryland was recently published, concluding: “…neurons are capable of transporting and metabolizing large quantities of lactate in vivo” and “…cultured neurons might preferentially oxidize lactate as their primary metabolic substrate”

Chase R. Figley. Human Brain: Implications for the Astrocyte-Neuron Lactate Shuttle Hypothesis. J Neuroscience, 2011, 31(13): 4768-4770; doi: 10.1523/​JNEUROSCI.6612-10.2011




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