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) 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.
Giant depolarizing potentials (GDPs), characteristic for the neonatal hippocampal slices exposed to artificial cerebrospinal fluid, is strongly inhibited by complementary energy substrates and this effect is unlikely to be caused by a subtle intracellular acidification induced by these compounds”Source:Inhibition of spontaneous network activity in neonatal hippocampal slices by energy substrates is not correlated with intracellular acidification. Mukhtarov M, Ivanov A, Zilberter Y, Bregestovski P. J Neurochem. 2011 Jan;116(2):316-21.
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.
- 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.
- 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.
- 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.
- 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.
- Khakhalin A (May 18, 2011). Questioning the depolarizing effects of GABA during early brain development. J Neurophysiol doi:10.1152/jn.00293.2011</a>.</p>
- 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)
- Lehninger, A.L. (2005). “Oxydative phosphorylation and photophosphorylation,” in Principles of biochemistry, eds. D.L. Nelson & M.M. Cox. Forth ed: W. H. Freeman), 690-740.
- 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.
- 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.