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The influence of moderate hypercapnia on neural activity in the anesthetized nonhuman primate.

Zappe AC, Uludağ K, Oeltermann A, Uğurbil K, Logothetis NK - Cereb. Cortex (2008)

Bottom Line: Such methods, however, assume that hypercapnia has no direct effect on CMRO(2).In contrast to this, spontaneous fluctuations of local field potentials in the beta and gamma frequency range as well as multiunit activity are reduced by approximately 15% during inhalation of 6% CO(2) (pCO(2) = 56 mmHg).A strong tendency toward a reduction of neuronal activity was also found at CO(2) inhalation of 3% (pCO(2) = 45 mmHg).

View Article: PubMed Central - PubMed

Affiliation: Max-Planck Institute for Biological Cybernetics, Spemannstrasse 38, 72076 Tübingen, Germany. aczappe@tuebingen.mpg.de

ABSTRACT
Hypercapnia is often used as vasodilatory challenge in clinical applications and basic research. In functional magnetic resonance imaging (fMRI), elevated CO(2) is applied to derive stimulus-induced changes in the cerebral rate of oxygen consumption (CMRO(2)) by measuring cerebral blood flow and blood-oxygenation-level-dependent (BOLD) signal. Such methods, however, assume that hypercapnia has no direct effect on CMRO(2). In this study, we used combined intracortical recordings and fMRI in the visual cortex of anesthetized macaque monkeys to show that spontaneous neuronal activity is in fact significantly reduced by moderate hypercapnia. As expected, measurement of cerebral blood volume using an exogenous contrast agent and of BOLD signal showed that both are increased during hypercapnia. In contrast to this, spontaneous fluctuations of local field potentials in the beta and gamma frequency range as well as multiunit activity are reduced by approximately 15% during inhalation of 6% CO(2) (pCO(2) = 56 mmHg). A strong tendency toward a reduction of neuronal activity was also found at CO(2) inhalation of 3% (pCO(2) = 45 mmHg). This suggests that CMRO(2) might be reduced during hypercapnia and caution must be exercised when hypercapnia is applied to calibrate the BOLD signal.

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Related in: MedlinePlus

Model calculation shows how the coupling constant n between fractional changes of CBF and CMRO2 would be affected if spontaneous activity and hence CMRO2 is altered by hypercapnia, illustrated here with data taken from the literature (Davis et al. 1998; Stefanovic et al. 2006). The gray line at 0% CMRO2 indicates the value assumed by the calibrated BOLD approach.
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fig5: Model calculation shows how the coupling constant n between fractional changes of CBF and CMRO2 would be affected if spontaneous activity and hence CMRO2 is altered by hypercapnia, illustrated here with data taken from the literature (Davis et al. 1998; Stefanovic et al. 2006). The gray line at 0% CMRO2 indicates the value assumed by the calibrated BOLD approach.

Mentions: In the following, we illustrate how the estimation of CMRO2 calculated by calibrated BOLD is affected for 2 data sets; one study with a rather small CBF change around 18% by Davis et al. (1998) and a second data set with a larger CBF change of up to 80% by Stefanovic et al. (2006). In the study by Davis et al. (1998), the BOLD signal and CBF changed during hypercapnia by 1.8% and 18%, respectively, and during visual stimulation by 1.7% and 45%; in the study by Stefanovic et al. (Fig. 5 in 2006) changes of ΔBOLD = 3.7% and ΔCBF = 80% can be found during hypercapnia and ΔBOLD = 2.7% and ΔCBF = 90% during visual stimulation. Using the algorithm described in Methods, the resulting coupling constant n is shown in Figure 5 as a function of ΔCMRO2 during hypercapnia. As can be seen, a CMRO2 decrease during hypercapnia leads to an increase in the calculated coupling constant n, that is, leads to a smaller calculated ΔCMRO2 for the same ΔCBF during stimulation. In other words, the larger the reduction in CMRO2 during hypercapnia is, the larger is the estimate of n during stimulation.


The influence of moderate hypercapnia on neural activity in the anesthetized nonhuman primate.

Zappe AC, Uludağ K, Oeltermann A, Uğurbil K, Logothetis NK - Cereb. Cortex (2008)

Model calculation shows how the coupling constant n between fractional changes of CBF and CMRO2 would be affected if spontaneous activity and hence CMRO2 is altered by hypercapnia, illustrated here with data taken from the literature (Davis et al. 1998; Stefanovic et al. 2006). The gray line at 0% CMRO2 indicates the value assumed by the calibrated BOLD approach.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC2567427&req=5

fig5: Model calculation shows how the coupling constant n between fractional changes of CBF and CMRO2 would be affected if spontaneous activity and hence CMRO2 is altered by hypercapnia, illustrated here with data taken from the literature (Davis et al. 1998; Stefanovic et al. 2006). The gray line at 0% CMRO2 indicates the value assumed by the calibrated BOLD approach.
Mentions: In the following, we illustrate how the estimation of CMRO2 calculated by calibrated BOLD is affected for 2 data sets; one study with a rather small CBF change around 18% by Davis et al. (1998) and a second data set with a larger CBF change of up to 80% by Stefanovic et al. (2006). In the study by Davis et al. (1998), the BOLD signal and CBF changed during hypercapnia by 1.8% and 18%, respectively, and during visual stimulation by 1.7% and 45%; in the study by Stefanovic et al. (Fig. 5 in 2006) changes of ΔBOLD = 3.7% and ΔCBF = 80% can be found during hypercapnia and ΔBOLD = 2.7% and ΔCBF = 90% during visual stimulation. Using the algorithm described in Methods, the resulting coupling constant n is shown in Figure 5 as a function of ΔCMRO2 during hypercapnia. As can be seen, a CMRO2 decrease during hypercapnia leads to an increase in the calculated coupling constant n, that is, leads to a smaller calculated ΔCMRO2 for the same ΔCBF during stimulation. In other words, the larger the reduction in CMRO2 during hypercapnia is, the larger is the estimate of n during stimulation.

Bottom Line: Such methods, however, assume that hypercapnia has no direct effect on CMRO(2).In contrast to this, spontaneous fluctuations of local field potentials in the beta and gamma frequency range as well as multiunit activity are reduced by approximately 15% during inhalation of 6% CO(2) (pCO(2) = 56 mmHg).A strong tendency toward a reduction of neuronal activity was also found at CO(2) inhalation of 3% (pCO(2) = 45 mmHg).

View Article: PubMed Central - PubMed

Affiliation: Max-Planck Institute for Biological Cybernetics, Spemannstrasse 38, 72076 Tübingen, Germany. aczappe@tuebingen.mpg.de

ABSTRACT
Hypercapnia is often used as vasodilatory challenge in clinical applications and basic research. In functional magnetic resonance imaging (fMRI), elevated CO(2) is applied to derive stimulus-induced changes in the cerebral rate of oxygen consumption (CMRO(2)) by measuring cerebral blood flow and blood-oxygenation-level-dependent (BOLD) signal. Such methods, however, assume that hypercapnia has no direct effect on CMRO(2). In this study, we used combined intracortical recordings and fMRI in the visual cortex of anesthetized macaque monkeys to show that spontaneous neuronal activity is in fact significantly reduced by moderate hypercapnia. As expected, measurement of cerebral blood volume using an exogenous contrast agent and of BOLD signal showed that both are increased during hypercapnia. In contrast to this, spontaneous fluctuations of local field potentials in the beta and gamma frequency range as well as multiunit activity are reduced by approximately 15% during inhalation of 6% CO(2) (pCO(2) = 56 mmHg). A strong tendency toward a reduction of neuronal activity was also found at CO(2) inhalation of 3% (pCO(2) = 45 mmHg). This suggests that CMRO(2) might be reduced during hypercapnia and caution must be exercised when hypercapnia is applied to calibrate the BOLD signal.

Show MeSH
Related in: MedlinePlus