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Patch-clamp recordings of rat neurons from acute brain slices of the somatosensory cortex during magnetic stimulation.

Pashut T, Magidov D, Ben-Porat H, Wolfus S, Friedman A, Perel E, Lavidor M, Bar-Gad I, Yeshurun Y, Korngreen A - Front Cell Neurosci (2014)

Bottom Line: Although transcranial magnetic stimulation (TMS) is a popular tool for both basic research and clinical applications, its actions on nerve cells are only partially understood.In agreement with the modeling, our recordings demonstrate the dependence of magnetic stimulation-triggered action potentials on the type and state of the neuron and its orientation within the magnetic field.Our results suggest that the observed effects of TMS are deeply rooted in the biophysical properties of single neurons in the central nervous system and provide a framework both for interpreting existing TMS data and developing new simulation-based tools and therapies.

View Article: PubMed Central - PubMed

Affiliation: The Leslie and Susan Gonda Multidisciplinary Brain Research Center, Bar-Ilan University Ramat-Gan, Israel.

ABSTRACT
Although transcranial magnetic stimulation (TMS) is a popular tool for both basic research and clinical applications, its actions on nerve cells are only partially understood. We have previously predicted, using compartmental modeling, that magnetic stimulation of central nervous system neurons depolarized the soma followed by initiation of an action potential in the initial segment of the axon. The simulations also predict that neurons with low current threshold are more susceptible to magnetic stimulation. Here we tested these theoretical predictions by combining in vitro patch-clamp recordings from rat brain slices with magnetic stimulation and compartmental modeling. In agreement with the modeling, our recordings demonstrate the dependence of magnetic stimulation-triggered action potentials on the type and state of the neuron and its orientation within the magnetic field. Our results suggest that the observed effects of TMS are deeply rooted in the biophysical properties of single neurons in the central nervous system and provide a framework both for interpreting existing TMS data and developing new simulation-based tools and therapies.

No MeSH data available.


Related in: MedlinePlus

A magnetic pulse evoked an action potential. (A) Schematic drawing of the experimental layout. The induced electric field of the coil in the plane of the brain slice was calculated and is displayed in pseudocolor. A reconstructed L5 pyramidal neuron is overlaid on this drawing to indicate the approximate position of this neuron during the recording. The area around this neuron is enlarged on the right. Note that the induced electric field is different in the right and left panels. (B) A subthreshold response to the magnetic field recorded with the patch-clamp system using the loose-patch configuration. The electrode recorded the artifact caused by the magnetic stimulation. Magnetic stimulation was 0.7 T. (C) A suprathreshold neuron reaction to the magnetic stimulation. Magnetic stimulation was 0.9 T. (D) The recorded trace without the action potential (B) was subtracted from the trace with the action potential (C). This allowed isolation of the action potential waveform (black). A spontaneous action potential is displayed in red over the action potential generated by the magnetic stimulation.
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Figure 3: A magnetic pulse evoked an action potential. (A) Schematic drawing of the experimental layout. The induced electric field of the coil in the plane of the brain slice was calculated and is displayed in pseudocolor. A reconstructed L5 pyramidal neuron is overlaid on this drawing to indicate the approximate position of this neuron during the recording. The area around this neuron is enlarged on the right. Note that the induced electric field is different in the right and left panels. (B) A subthreshold response to the magnetic field recorded with the patch-clamp system using the loose-patch configuration. The electrode recorded the artifact caused by the magnetic stimulation. Magnetic stimulation was 0.7 T. (C) A suprathreshold neuron reaction to the magnetic stimulation. Magnetic stimulation was 0.9 T. (D) The recorded trace without the action potential (B) was subtracted from the trace with the action potential (C). This allowed isolation of the action potential waveform (black). A spontaneous action potential is displayed in red over the action potential generated by the magnetic stimulation.

Mentions: We investigated the response of a single neuron to magnetic stimulation by combining a patch-clamp setup with a magnetic coil (Figures 1, 2 in Methods). A patch electrode was attached to a layer 5 (L5) pyramidal neuron from the somatosensory cortex in the loose-patch configuration. Then, to obtain optimal stimulation, the magnetic coil was positioned with its median radius below the neuron (Figures 3A, 1A). At low stimulation intensities only a stimulus artifact was observed (Figure 3B). Increasing the intensity elicited a biphasic waveform, partially obscured by the stimulus artifact, resembling an extracellular action potential (Figure 3C). This waveform was isolated by scaling and subtracting traces recorded at low magnetic stimulation intensities from traces displaying an apparent action potential waveforms (Figure 3D). The shape of a spontaneous action potential recorded from the same neuron was identical to that triggered by magnetic stimulation (Figure 3D). Gradually increasing magnetic stimulation allowed determination of the minimal magnetic stimulation intensity required to generate an action potential. This threshold stimulation intensity is referred to as the magnetic threshold of the neuron (reported here in units of the magnetic field amplitude, Tesla, at the center of the coil). To verify that the observed waveform was indeed that of an action potential we added 100 nM tetrodotoxin to the bath solution which eliminated the action potential waveform from the loose-patch recording (Figure 4A). Similar results were obtained from three other neurons exposed to tetrodotoxin. It is well known that the induced electric field at the center of a round coil is zero and, therefore, should not stimulate action potentials. To test this we first measured the magnetic threshold of a neuron when the coil was positioned with its median radius below the neuron (Figure 4B). We then moved the coil so that the center of the coil was below that same neuron while remaining in the loose-patch configuration. As expected, the same magnetic stimulation did not induce an action potential (Figure 4B). Similar results were observed in four other neurons. This experiment verified that the induced action potential was indeed due to magnetic stimulation.


Patch-clamp recordings of rat neurons from acute brain slices of the somatosensory cortex during magnetic stimulation.

Pashut T, Magidov D, Ben-Porat H, Wolfus S, Friedman A, Perel E, Lavidor M, Bar-Gad I, Yeshurun Y, Korngreen A - Front Cell Neurosci (2014)

A magnetic pulse evoked an action potential. (A) Schematic drawing of the experimental layout. The induced electric field of the coil in the plane of the brain slice was calculated and is displayed in pseudocolor. A reconstructed L5 pyramidal neuron is overlaid on this drawing to indicate the approximate position of this neuron during the recording. The area around this neuron is enlarged on the right. Note that the induced electric field is different in the right and left panels. (B) A subthreshold response to the magnetic field recorded with the patch-clamp system using the loose-patch configuration. The electrode recorded the artifact caused by the magnetic stimulation. Magnetic stimulation was 0.7 T. (C) A suprathreshold neuron reaction to the magnetic stimulation. Magnetic stimulation was 0.9 T. (D) The recorded trace without the action potential (B) was subtracted from the trace with the action potential (C). This allowed isolation of the action potential waveform (black). A spontaneous action potential is displayed in red over the action potential generated by the magnetic stimulation.
© Copyright Policy - open-access
Related In: Results  -  Collection

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Show All Figures
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Figure 3: A magnetic pulse evoked an action potential. (A) Schematic drawing of the experimental layout. The induced electric field of the coil in the plane of the brain slice was calculated and is displayed in pseudocolor. A reconstructed L5 pyramidal neuron is overlaid on this drawing to indicate the approximate position of this neuron during the recording. The area around this neuron is enlarged on the right. Note that the induced electric field is different in the right and left panels. (B) A subthreshold response to the magnetic field recorded with the patch-clamp system using the loose-patch configuration. The electrode recorded the artifact caused by the magnetic stimulation. Magnetic stimulation was 0.7 T. (C) A suprathreshold neuron reaction to the magnetic stimulation. Magnetic stimulation was 0.9 T. (D) The recorded trace without the action potential (B) was subtracted from the trace with the action potential (C). This allowed isolation of the action potential waveform (black). A spontaneous action potential is displayed in red over the action potential generated by the magnetic stimulation.
Mentions: We investigated the response of a single neuron to magnetic stimulation by combining a patch-clamp setup with a magnetic coil (Figures 1, 2 in Methods). A patch electrode was attached to a layer 5 (L5) pyramidal neuron from the somatosensory cortex in the loose-patch configuration. Then, to obtain optimal stimulation, the magnetic coil was positioned with its median radius below the neuron (Figures 3A, 1A). At low stimulation intensities only a stimulus artifact was observed (Figure 3B). Increasing the intensity elicited a biphasic waveform, partially obscured by the stimulus artifact, resembling an extracellular action potential (Figure 3C). This waveform was isolated by scaling and subtracting traces recorded at low magnetic stimulation intensities from traces displaying an apparent action potential waveforms (Figure 3D). The shape of a spontaneous action potential recorded from the same neuron was identical to that triggered by magnetic stimulation (Figure 3D). Gradually increasing magnetic stimulation allowed determination of the minimal magnetic stimulation intensity required to generate an action potential. This threshold stimulation intensity is referred to as the magnetic threshold of the neuron (reported here in units of the magnetic field amplitude, Tesla, at the center of the coil). To verify that the observed waveform was indeed that of an action potential we added 100 nM tetrodotoxin to the bath solution which eliminated the action potential waveform from the loose-patch recording (Figure 4A). Similar results were obtained from three other neurons exposed to tetrodotoxin. It is well known that the induced electric field at the center of a round coil is zero and, therefore, should not stimulate action potentials. To test this we first measured the magnetic threshold of a neuron when the coil was positioned with its median radius below the neuron (Figure 4B). We then moved the coil so that the center of the coil was below that same neuron while remaining in the loose-patch configuration. As expected, the same magnetic stimulation did not induce an action potential (Figure 4B). Similar results were observed in four other neurons. This experiment verified that the induced action potential was indeed due to magnetic stimulation.

Bottom Line: Although transcranial magnetic stimulation (TMS) is a popular tool for both basic research and clinical applications, its actions on nerve cells are only partially understood.In agreement with the modeling, our recordings demonstrate the dependence of magnetic stimulation-triggered action potentials on the type and state of the neuron and its orientation within the magnetic field.Our results suggest that the observed effects of TMS are deeply rooted in the biophysical properties of single neurons in the central nervous system and provide a framework both for interpreting existing TMS data and developing new simulation-based tools and therapies.

View Article: PubMed Central - PubMed

Affiliation: The Leslie and Susan Gonda Multidisciplinary Brain Research Center, Bar-Ilan University Ramat-Gan, Israel.

ABSTRACT
Although transcranial magnetic stimulation (TMS) is a popular tool for both basic research and clinical applications, its actions on nerve cells are only partially understood. We have previously predicted, using compartmental modeling, that magnetic stimulation of central nervous system neurons depolarized the soma followed by initiation of an action potential in the initial segment of the axon. The simulations also predict that neurons with low current threshold are more susceptible to magnetic stimulation. Here we tested these theoretical predictions by combining in vitro patch-clamp recordings from rat brain slices with magnetic stimulation and compartmental modeling. In agreement with the modeling, our recordings demonstrate the dependence of magnetic stimulation-triggered action potentials on the type and state of the neuron and its orientation within the magnetic field. Our results suggest that the observed effects of TMS are deeply rooted in the biophysical properties of single neurons in the central nervous system and provide a framework both for interpreting existing TMS data and developing new simulation-based tools and therapies.

No MeSH data available.


Related in: MedlinePlus