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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

Anatomical slice showing 2 electrodes positioned in gray matter of macaque V1. The image was obtained after infusion of MION and as a consequence vessels and especially the intracortical veins appear dark. The distance between the electrodes is ∼5 mm. The outline of the electrode appears artificially enlarged because of the susceptibility artifact. Thus, the real dimensions of the electrode are indicated by a sketch at the right penetration site.
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fig1: Anatomical slice showing 2 electrodes positioned in gray matter of macaque V1. The image was obtained after infusion of MION and as a consequence vessels and especially the intracortical veins appear dark. The distance between the electrodes is ∼5 mm. The outline of the electrode appears artificially enlarged because of the susceptibility artifact. Thus, the real dimensions of the electrode are indicated by a sketch at the right penetration site.

Mentions: fMRI was performed with a 25 mm surface coil, acquiring 2-shot gradient-echo echo planar imaging pulse sequences with time repetition/time echo = 250/16 ms and flip angle = 20°. Two axial slices were collected at 0.75 × 0.75 mm2 in-plane resolution and 2-mm thickness. In addition, an anatomical scan was acquired to visualize the location of the electrode tip in the cortex (FLASH sequence TR/TE 2000/8.5 ms, 0.5-mm slice thickness, 187.5 × 187.5 μm2, see Fig. 1). In 2 of the sessions, CBV imaging with monocrystalline iron oxide nanocolloid (MION) was performed in order to assess blood volume changes in the small parenchymal vessels (Mandeville et al. 1998; Mandeville and Marota 1999). MION was injected intravenously at the end of the session (8 mg/kg, citrate-buffered), which suppressed the MR signal in striate cortex (area V1) to ∼50% of preinjection levels. After waiting 5-min postinjection for signal stabilization, CBV imaging was performed using the same MR parameters as in BOLD imaging. BOLD data on the transient hypercapnic phase were obtained in 18 scans recorded in 5 sessions and 3 animals. The CBV time course of the transient hypercapnic phase was obtained in 2 scans on 2 different sessions and animals.


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)

Anatomical slice showing 2 electrodes positioned in gray matter of macaque V1. The image was obtained after infusion of MION and as a consequence vessels and especially the intracortical veins appear dark. The distance between the electrodes is ∼5 mm. The outline of the electrode appears artificially enlarged because of the susceptibility artifact. Thus, the real dimensions of the electrode are indicated by a sketch at the right penetration site.
© Copyright Policy - open-access
Related In: Results  -  Collection

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

fig1: Anatomical slice showing 2 electrodes positioned in gray matter of macaque V1. The image was obtained after infusion of MION and as a consequence vessels and especially the intracortical veins appear dark. The distance between the electrodes is ∼5 mm. The outline of the electrode appears artificially enlarged because of the susceptibility artifact. Thus, the real dimensions of the electrode are indicated by a sketch at the right penetration site.
Mentions: fMRI was performed with a 25 mm surface coil, acquiring 2-shot gradient-echo echo planar imaging pulse sequences with time repetition/time echo = 250/16 ms and flip angle = 20°. Two axial slices were collected at 0.75 × 0.75 mm2 in-plane resolution and 2-mm thickness. In addition, an anatomical scan was acquired to visualize the location of the electrode tip in the cortex (FLASH sequence TR/TE 2000/8.5 ms, 0.5-mm slice thickness, 187.5 × 187.5 μm2, see Fig. 1). In 2 of the sessions, CBV imaging with monocrystalline iron oxide nanocolloid (MION) was performed in order to assess blood volume changes in the small parenchymal vessels (Mandeville et al. 1998; Mandeville and Marota 1999). MION was injected intravenously at the end of the session (8 mg/kg, citrate-buffered), which suppressed the MR signal in striate cortex (area V1) to ∼50% of preinjection levels. After waiting 5-min postinjection for signal stabilization, CBV imaging was performed using the same MR parameters as in BOLD imaging. BOLD data on the transient hypercapnic phase were obtained in 18 scans recorded in 5 sessions and 3 animals. The CBV time course of the transient hypercapnic phase was obtained in 2 scans on 2 different sessions and animals.

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