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High-field MRI: a premiere in functional observation, neuron by neuron


Thanks to a high-field MRI scanner, researchers from the CEA-I2BM followed the dynamics of ion exchange in neurons, which conduct the propagation of nerve impulses. Their model: Aplysia, a marine mollusk widely used in neuroscience for the study of learning and memory.

Published on 29 May 2013
The exchange of ions across neuronal membranes gives rise to an “electric discharge”, namely an action potential that determines the passage of nerve impulses from one neuron to the next. The issue for microscopic imaging is to follow the dynamics of these exchanges along neuronal circuits in different biochemical conditions. Such studies are opening a new field of investigation to cognitive neuroscience and drug development. Thanks to NeuroSpin’s high-field MRI device (17.2 Tesla) dedicated to small animals, teams from the CEA-I2BM are developing imaging techniques in living cells to bridge the results between biological imaging on tissue sections and in vivo imaging. The first offers a spatial resolution of about 10 microns [1], while the second has a resolution from 100 – 200 microns.

The researchers worked with Aplysia, a classic model animal in neuroscience with a small set of large neurons (from several hundred microns to 1 mm in size). The neurons are therefore also observable by high-resolution in vivo imaging. The scientists have shown for the first time that the dynamics of transporting manganese ions (analogous to calcium) in the motor neurons of the Aplysia buccal ganglion are modulated by the neurotransmitter dopamine. To do this, they used high-field MRI to observe Aplysia neurons in medium with a low manganese concentration, so as to not disrupt cell physiology. They showed that stimulation of neurons with dopamine alters the dynamics of manganese ions, particularly their elimination by neurons. This is the first time that such a modulation is revealed in a network where each neuron is visible by MRI, thanks to its very advanced spatial resolution.

The exchange of ions across neuronal membranes gives rise to an “electric discharge”, namely an action potential that determines the passage of nerve impulses from one neuron to the next. The issue for microscopic imaging is to follow the dynamics of these exchanges along neuronal circuits in different biochemical conditions. Such studies are opening a new field of investigation to cognitive neuroscience and drug development. Thanks to NeuroSpin’s high-field MRI device (17.2 Tesla) dedicated to small animals, teams from the CEA-I2BM are developing imaging techniques in living cells to bridge the results between biological imaging on tissue sections and in vivo imaging. The first offers a spatial resolution of about 10 microns [1], while the second has a resolution from 100 – 200 microns.

The researchers worked with Aplysia, a classic model animal in neuroscience with a small set of large neurons (from several hundred microns to 1 mm in size). The neurons are therefore also observable by high-resolution in vivo imaging. The scientists have shown for the first time that the dynamics of transporting manganese ions (analogous to calcium) in the motor neurons of the Aplysia buccal ganglion are modulated by the neurotransmitter dopamine. To do this, they used high-field MRI to observe Aplysia neurons in medium with a low manganese concentration, so as to not disrupt cell physiology. They showed that stimulation of neurons with dopamine alters the dynamics of manganese ions, particularly their elimination by neurons. This is the first time that such a modulation is revealed in a network where each neuron is visible by MRI, thanks to its very advanced spatial resolution.

 

A. Aplysia californica. B. Schéma du ganglion buccal. Le code couleur relie les corps cellulaires aux nerfs périphériques qui reçoivent leurs axones. C. Rendu 3D d’images par résonance magnétique, après migration du manganèse le long du nerf 3. Les neurones qui ont accumulé du manganèse (en vert) sont ceux avec des projections axonales dans le nerf 3

[1] 1 micron= 10-6 mete

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