EVENT

Brain active transmembrane water cycling measured by MR is associated with neuronal activity(2018). DOI: 10.1002/mrm.27473CV.pdf


Ruiliang Bai,Charles S. Springer Jr.,Dietmar Plenz, Peter J. Basser

 

Significance

We found that neurons absorb and release water when they relay messages throughout the brain. Tracking this water movement with imaging technology may one day provide valuable information on normal brain activity, as well as how injury or disease affect brain function.

Current functional magnetic resonance imaging (fMRI) technologies measure neuronal activity indirectly by tracking changes in blood flow and blood oxygen levels. Neurons communicate with each other by a process known as firing. In this process, they emit a slight electrical charge as an enzyme moves positively charged molecules — potassium and sodium ions — through the cell membrane. In the current study, when we stimulated cell cultures of rat neurons to fire, we found that the exchanges of potassium and sodium ions was accompanied by an increase in the number of water molecules moving into and out of the cell.

We noted that our method works only in cultures of neurons and additional studies are necessary to advance the technology so that it can be used to monitor neuronal firing in living organisms.

Abstract

Purpose: fMRI is widely used to study brain activity. Unfortunately, conventional fMRI methods assess neuronal activity only indirectly, through hemodynamic coupling. Here, we show that active, steadystate transmembrane water cycling (AWC) could serve as a basis for a potential fMRI mechanism for direct neuronal activity detection.

Methods: AWC and neuronal actitivity in rat organotypic cortical cultures were simultaneously measured with a hybrid MRfluorescence system. Perfusion with a paramagnetic MRI contrast agent, Gadoteridol, allows NMR determination of the kinetics of transcytolemmal water exchange. Changes in intracellular calcium concentration, [Cai2+] were used as a proxy of neuronal activity and were monitored by fluorescence imaging.

Results: When we alter neuronal activity by titrating with extracellular [K+] near the normal value, we see an AWC response resembling Na+K+ATPase (NKA) MichaelisMenten behavior. When we treat with the voltagegated sodium channel inhibitor, or with an excitatory postsynaptic inhibitor cocktail, we see AWC decrease by up to 71%. AWC was found also to be positively correlated with the basal level of spontaneous activity, which varies in different cultures.

Conclusions: These results suggest that AWC is associated with neuronal activity and NKA activity is a major contributor in coupling AWC to neuronal activity. Although AWC comprises steadystate, homeostatic transmembrane water exchange, our analysis also yields a simultaneous measure of the average cell volume, which reports any slower net transmembrane water transport.

Keywords

active, fMRI, functional MRI, membrane, transcytolemmal, Na+/K+ ATPase, neuronal activity, pump, water exchange

Online paper: https://doi.org/10.1002/mrm.27473

2018-10-18 READ MORE

Brain active transmembrane water cycling measured by MR is associated with neuronal activity(2018). DOI: 10.1002/mrm.27473CV.pdf


Ruiliang Bai,Charles S. Springer Jr.,Dietmar Plenz, Peter J. Basser

 

Significance

We found that neurons absorb and release water when they relay messages throughout the brain. Tracking this water movement with imaging technology may one day provide valuable information on normal brain activity, as well as how injury or disease affect brain function.

Current functional magnetic resonance imaging (fMRI) technologies measure neuronal activity indirectly by tracking changes in blood flow and blood oxygen levels. Neurons communicate with each other by a process known as firing. In this process, they emit a slight electrical charge as an enzyme moves positively charged molecules — potassium and sodium ions — through the cell membrane. In the current study, when we stimulated cell cultures of rat neurons to fire, we found that the exchanges of potassium and sodium ions was accompanied by an increase in the number of water molecules moving into and out of the cell.

We noted that our method works only in cultures of neurons and additional studies are necessary to advance the technology so that it can be used to monitor neuronal firing in living organisms.

Abstract

Purpose: fMRI is widely used to study brain activity. Unfortunately, conventional fMRI methods assess neuronal activity only indirectly, through hemodynamic coupling. Here, we show that active, steadystate transmembrane water cycling (AWC) could serve as a basis for a potential fMRI mechanism for direct neuronal activity detection.

Methods: AWC and neuronal actitivity in rat organotypic cortical cultures were simultaneously measured with a hybrid MRfluorescence system. Perfusion with a paramagnetic MRI contrast agent, Gadoteridol, allows NMR determination of the kinetics of transcytolemmal water exchange. Changes in intracellular calcium concentration, [Cai2+] were used as a proxy of neuronal activity and were monitored by fluorescence imaging.

Results: When we alter neuronal activity by titrating with extracellular [K+] near the normal value, we see an AWC response resembling Na+K+ATPase (NKA) MichaelisMenten behavior. When we treat with the voltagegated sodium channel inhibitor, or with an excitatory postsynaptic inhibitor cocktail, we see AWC decrease by up to 71%. AWC was found also to be positively correlated with the basal level of spontaneous activity, which varies in different cultures.

Conclusions: These results suggest that AWC is associated with neuronal activity and NKA activity is a major contributor in coupling AWC to neuronal activity. Although AWC comprises steadystate, homeostatic transmembrane water exchange, our analysis also yields a simultaneous measure of the average cell volume, which reports any slower net transmembrane water transport.

Keywords

active, fMRI, functional MRI, membrane, transcytolemmal, Na+/K+ ATPase, neuronal activity, pump, water exchange

Online Paper: https://doi.org/10.1002/mrm.27473

2018-10-18 READ MORE

Functionally specific optogenetic modulation in primate visual cortex

Mykyta M. Chernov, Robert M. Friedman, Gang Chen, Gene R. Stoner, and Anna Wang Roe/ PNAS October 9, 2018 115 (41) 10505-10510; published ahead of print September 26, 2018 https://doi.org/10.1073/pnas.1802018115 

 

Significance

Primate visual cortex is organized into columns that process different features of a visual scene, such as color, orientation preference, and ocular dominance. Until now, their small size has made it difficult to modulate them directly. Here, we report for the first time that focal targeting of light-sensitive ion channels (channelrhodopsins) in macaques using lentiviral vectors allows one to stimulate functional domains. We show that such targeted stimulation leads to selective activation of anatomically connected neighboring domains with similar function. Such a fine-scale optical stimulation approach is capable of mapping functionally specific domain-based neuronal networks. Its potential for linking such networks to optogenetic modulation of perception and behavior opens doors for developing targeted, domain-based neuroprosthetics.

Abstract

In primates, visual perception is mediated by brain circuits composed of submillimeter nodes linked together in specific networks that process different types of information, such as eye specificity and contour orientation. We hypothesized that optogenetic stimulation targeted to cortical nodes could selectively activate such cortical networks. We used viral transfection methods to confer light sensitivity to neurons in monkey primary visual cortex. Using intrinsic signal optical imaging and single-unit electrophysiology to assess effects of targeted optogenetic stimulation, we found that (i) optogenetic stimulation of single ocular dominance columns (eye-specific nodes) revealed preferential activation of nearby same-eye columns but not opposite-eye columns, and (ii) optogenetic stimulation of single orientation domains increased visual response of matching orientation domains and relatively suppressed nonmatching orientation selectivity. These findings demonstrate that optical stimulation of single nodes leads to modulation of functionally specific cortical networks related to underlying neural architecture.

Link: http://www.pnas.org/content/115/41/10505

2018-10-18 READ MORE

Functionally specific optogenetic modulation in primate visual cortex

Mykyta M. Chernov, Robert M. Friedman, Gang Chen, Gene R. Stoner, and Anna Wang Roe/ PNAS October 9, 2018 115 (41) 10505-10510; published ahead of print September 26, 2018 https://doi.org/10.1073/pnas.1802018115 

 

Significance

Primate visual cortex is organized into columns that process different features of a visual scene, such as color, orientation preference, and ocular dominance. Until now, their small size has made it difficult to modulate them directly. Here, we report for the first time that focal targeting of light-sensitive ion channels (channelrhodopsins) in macaques using lentiviral vectors allows one to stimulate functional domains. We show that such targeted stimulation leads to selective activation of anatomically connected neighboring domains with similar function. Such a fine-scale optical stimulation approach is capable of mapping functionally specific domain-based neuronal networks. Its potential for linking such networks to optogenetic modulation of perception and behavior opens doors for developing targeted, domain-based neuroprosthetics.

Abstract

In primates, visual perception is mediated by brain circuits composed of submillimeter nodes linked together in specific networks that process different types of information, such as eye specificity and contour orientation. We hypothesized that optogenetic stimulation targeted to cortical nodes could selectively activate such cortical networks. We used viral transfection methods to confer light sensitivity to neurons in monkey primary visual cortex. Using intrinsic signal optical imaging and single-unit electrophysiology to assess effects of targeted optogenetic stimulation, we found that (i) optogenetic stimulation of single ocular dominance columns (eye-specific nodes) revealed preferential activation of nearby same-eye columns but not opposite-eye columns, and (ii) optogenetic stimulation of single orientation domains increased visual response of matching orientation domains and relatively suppressed nonmatching orientation selectivity. These findings demonstrate that optical stimulation of single nodes leads to modulation of functionally specific cortical networks related to underlying neural architecture.

Link: http://www.pnas.org/content/115/41/10505

2018-10-18 READ MORE

Significance

Detection and analyzing visual motion is an important task for the visual system. In the past half a century, research on motion information processing has been focused primarily on the dorsal visual areas (e.g. area MT/V5). Other visual areas (e.g. V2, V4) are virtually unexplored in this aspect, despite the fact that the motion-sensitive neurons in these areas are significantly present and form functional domains. In this study, we combined optical imaging with single-cell recordings to specifically record from direction-selective neurons in the second largest visual area, V2, in macaque monkeys, in order to have a full picture of how motion information is analyzed in the brain.

We found that motion-sensitive neurons in area V2 have characteristic features that are different from those in the well-studied motion areas like area MT. Particularly, these neurons have small receptive field and strong surround suppression, which make them sensitive to “motion contrast”, a key information delineating object boundaries. These features suggest that area V2 detects visual objects based on motion information.

Abstract

In the primate visual system, direction-selective (DS)neurons are critical for visual motion perception. While DS neurons in the dorsal visual pathway have been well characterized, the response properties of DS neurons in other major visual areas are largely unexplored. Recent optical imaging studies in monkey visual cortex area 2 (V2) revealed clusters of DS neurons. This imaging method facilitates targeted recordings from these neurons. Using optical imaging and single-cell recording, we characterized detailed response properties of DS neurons in macaque V2. Compared with DS neurons in the dorsal areas (e.g., middle temporal area [MT]), V2 DS neurons have a smaller receptive field and a stronger antagonistic surround. They do not code speed or plaid motion but are sensitive to motion contrast. Our results suggest that V2 DS neurons play an important role in figure-ground segregation. The clusters of V2 DS neurons are likely specialized functional systems for detecting motion contrast. 

Keywords

Macaque, V2, direction selectivity, RF surround, motion contrast

Online paper: https://www.cell.com/cell-reports/fulltext/S2211-1247(18)31444-X#secsectitle0265pdf.pdf

2018-10-17 READ MORE


Significance

Detection and analyzing visual motion is an important task for the visual system. In the past half a century, research on motion information processing has been focused primarily on the dorsal visual areas (e.g. area MT/V5). Other visual areas (e.g. V2, V4) are virtually unexplored in this aspect, despite the fact that the motion-sensitive neurons in these areas are significantly present and form functional domains. In this study, we combined optical imaging with single-cell recordings to specifically record from direction-selective neurons in the second largest visual area, V2, in macaque monkeys, in order to have a full picture of how motion information is analyzed in the brain.

We found that motion-sensitive neurons in area V2 have characteristic features that are different from those in the well-studied motion areas like area MT. Particularly, these neurons have small receptive field and strong surround suppression, which make them sensitive to “motion contrast”, a key information delineating object boundaries. These features suggest that area V2 detects visual objects based on motion information.

Abstract

In the primate visual system, direction-selective (DS)neurons are critical for visual motion perception. While DS neurons in the dorsal visual pathway have been well characterized, the response properties of DS neurons in other major visual areas are largely unexplored. Recent optical imaging studies in monkey visual cortex area 2 (V2) revealed clusters of DS neurons. This imaging method facilitates targeted recordings from these neurons. Using optical imaging and single-cell recording, we characterized detailed response properties of DS neurons in macaque V2. Compared with DS neurons in the dorsal areas (e.g., middle temporal area [MT]), V2 DS neurons have a smaller receptive field and a stronger antagonistic surround. They do not code speed or plaid motion but are sensitive to motion contrast. Our results suggest that V2 DS neurons play an important role in figure-ground segregation. The clusters of V2 DS neurons are likely specialized functional systems for detecting motion contrast. 

Keywords

Macaque, V2, direction selectivity, RF surround, motion contrast

Online paper: https://www.cell.com/cell-reports/fulltext/S2211-1247(18)31444-X#secsectitle0265pdf.pdf

2018-10-17 READ MORE
2018-10-11 READ MORE
2018-10-11 READ MORE
2018-10-11 READ MORE
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