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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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Time course of BOLD (gray) and MION (black) signals in primary visual cortex after the onset of 6% CO2 inhalation. The dotted lines give the saturation levels with the standard deviation of the saturation level shown as shaded boxes.
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fig4: Time course of BOLD (gray) and MION (black) signals in primary visual cortex after the onset of 6% CO2 inhalation. The dotted lines give the saturation levels with the standard deviation of the saturation level shown as shaded boxes.

Mentions: As expected, for both 3% and 6% hypercapnia challenges, the BOLD signal and the CBV increased (i.e., the T2*-weighted MR signal in the presence of MION decreased). During 6% CO2 administration, the BOLD signal was found to increase by 2.5 ± 0.3% (n = 5) and CBV-related MR signals were found to decrease by 23 ± 1% (n = 2) (see Fig. 4). This increase in CBV corresponds to a concomitant CBF increase which in this range can be approximated by a linear relationship with the slope of 0.38 resulting in ∼60% CBF change (Grubb et al. 1974; Lee et al. 2001), in agreement with our previous study which resulted in 60–100% CBF change for 6% CO2 (Zappe et al. 2008).


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)

Time course of BOLD (gray) and MION (black) signals in primary visual cortex after the onset of 6% CO2 inhalation. The dotted lines give the saturation levels with the standard deviation of the saturation level shown as shaded boxes.
© Copyright Policy - open-access
Related In: Results  -  Collection

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

fig4: Time course of BOLD (gray) and MION (black) signals in primary visual cortex after the onset of 6% CO2 inhalation. The dotted lines give the saturation levels with the standard deviation of the saturation level shown as shaded boxes.
Mentions: As expected, for both 3% and 6% hypercapnia challenges, the BOLD signal and the CBV increased (i.e., the T2*-weighted MR signal in the presence of MION decreased). During 6% CO2 administration, the BOLD signal was found to increase by 2.5 ± 0.3% (n = 5) and CBV-related MR signals were found to decrease by 23 ± 1% (n = 2) (see Fig. 4). This increase in CBV corresponds to a concomitant CBF increase which in this range can be approximated by a linear relationship with the slope of 0.38 resulting in ∼60% CBF change (Grubb et al. 1974; Lee et al. 2001), in agreement with our previous study which resulted in 60–100% CBF change for 6% CO2 (Zappe et al. 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.

Show MeSH
Related in: MedlinePlus