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. 2012 Apr 4;32(8):1472–1483. doi: 10.1038/jcbfm.2012.31

Figure 3.

Figure 3

Left: The plot shows the correlation between the rate of glucose oxidation, computed as one half of the sum of the tricarboxylic acid (TCA) cycle rates in the three cell types, and the rate of neurotransmitter cycling, intended as the sum of the rates of efflux in extracellular space (ECS) of glutamate and GABA from glutamatergic and GABAergic neurons, respectively. The round dots with relative horizontal and vertical error bars correspond to the medians and 68th percentiles around them of the samples of 100,000 steady states including Gaussian priors for the efflux of glutamate with mean values of 0.22, 0.30, 0.38, and 0.45 μmol/g per minute, and standard deviation 0.001 μmol/g per minute. Most of the horizontal error bar is due to the variability in GABA efflux, whereas the efflux of glutamate is tightly clustered around its mean value. The regression line that best fits the median points has equation y=0.89x+0.03. The lighter shade around it marks the 96th percentile, and the darker shade marks the 68th percentile. The values reported by Shen et al (1999) (▪), Gruetter et al (2001) (⧫), and by Lebon et al (2002) (▾), reported also in the graph, are in good agreement with the predictions of our model. Right: Histograms of the rate of release of glutamate (continuous curve) and GABA (dashed curve) in μmol/g per minute, in the three different steady states. The Gaussian shape of the distribution of the efflux rate of the neurotransmitter characterizing the steady state is a consequence of our entering the target values in the form of a Gaussian prior. The distribution of the rate of spontaneous release of GABA in AS and ES indicates that it is possible to have steady states with no GABA release at all, although some release of GABA appears more likely. In inhibitory steady state, the distribution of rates of glutamate release, widely distributed between 0 and 0.02, indicates that no release of glutamate is very unlikely. GABA, gamma aminobutyric acid; ES, excitatory steady state; AS, awake steady state.