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Neuronal and astroglial correlates underlying spatiotemporal intrinsic optical signal in the rat hippocampal slice.

Pál I, Nyitrai G, Kardos J, Héja L - PLoS ONE (2013)

Bottom Line: It was eliminated by tetrodotoxin blockade of voltage-gated Na(+) channels and was significantly enhanced by suppressing inhibitory signaling with gamma-aminobutyric acid(A) receptor antagonist picrotoxin.We found that IOS was predominantly initiated by postsynaptic Glu receptor activation and progressed by the activation of astroglial Glu transporters and Mg(2+)-independent astroglial N-methyl-D-aspartate receptors.Our model may help to better interpret in vivo IOS and support diagnosis in the future.

View Article: PubMed Central - PubMed

Affiliation: Department of Functional Pharmacology, Institute of Molecular Pharmacology, Research Centre for Natural Sciences, Hungarian Academy of Sciences, Budapest, Hungary. pal.ildiko@ttk.mta.hu

ABSTRACT
Widely used for mapping afferent activated brain areas in vivo, the label-free intrinsic optical signal (IOS) is mainly ascribed to blood volume changes subsequent to glial glutamate uptake. By contrast, IOS imaged in vitro is generally attributed to neuronal and glial cell swelling, however the relative contribution of different cell types and molecular players remained largely unknown. We characterized IOS to Schaffer collateral stimulation in the rat hippocampal slice using a 464-element photodiode-array device that enables IOS monitoring at 0.6 ms time-resolution in combination with simultaneous field potential recordings. We used brief half-maximal stimuli by applying a medium intensity 50 Volt-stimulus train within 50 ms (20 Hz). IOS was primarily observed in the str. pyramidale and proximal region of the str. radiatum of the hippocampus. It was eliminated by tetrodotoxin blockade of voltage-gated Na(+) channels and was significantly enhanced by suppressing inhibitory signaling with gamma-aminobutyric acid(A) receptor antagonist picrotoxin. We found that IOS was predominantly initiated by postsynaptic Glu receptor activation and progressed by the activation of astroglial Glu transporters and Mg(2+)-independent astroglial N-methyl-D-aspartate receptors. Under control conditions, role for neuronal K(+)/Cl(-) cotransporter KCC2, but not for glial Na(+)/K(+)/Cl(-) cotransporter NKCC1 was observed. Slight enhancement and inhibition of IOS through non-specific Cl(-) and volume-regulated anion channels, respectively, were also depicted. High-frequency IOS imaging, evoked by brief afferent stimulation in brain slices provide a new paradigm for studying mechanisms underlying IOS genesis. Major players disclosed this way imply that spatiotemporal IOS reflects glutamatergic neuronal activation and astroglial response, as observed within the hippocampus. Our model may help to better interpret in vivo IOS and support diagnosis in the future.

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Time course, stimulation dependency and regional distribution of IOS and field response.A left: Changes of IOS shape and amplitude with the increasing number of stimuli. Numbers above that curves indicate the stimulus number. Transparent lines show the fitted linear function to calculate the slope and decay of the IOS curves. A middle: Time course of the IOS and field response A right: Correlation between the number of diodes containing IOS and the stimulus number (R2 = 0.99). B Top left: Overview of the IOS signal on the 464 element photodiode array. Transparent lines indicate the pyramidal cell layer and the granular cell layer of the dentate gyrus (DG). The position of the stimulating electrode is marked by an arrow and the sites of field potential recording electrodes are indicated by colored elipses. B Bottom left: 3D representation of the IOS amplitude. The position of the stimulating and recording electrodes are marked by an arrow and an asteriks, respectively. The colorbar indicates the transmittance change compared to the resting light intensity. B Right: Representative IOS and field response traces recorded at different locations of the slice. The exact location of the traces are indicated by the coloured elipses on the Top Left image. C Left and Middle: 3D IOS amplitude maps before (left) and after (middle) making a cut between the stimulating electrode and CA3. Transparent line indicates the pyramidal layer. The position of the stimulating electrode is marked by an arrow and the site of field potential recording is indicated by an asterisk. C Right: Representative IOS traces near the recording electrode (marked by white asterisk) before (black) and after (red) making a cut between the stimulating electrode and CA3. The slight difference between the curves is due to the slightly decreased electrophysiological characteristics after making cut.
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pone-0057694-g001: Time course, stimulation dependency and regional distribution of IOS and field response.A left: Changes of IOS shape and amplitude with the increasing number of stimuli. Numbers above that curves indicate the stimulus number. Transparent lines show the fitted linear function to calculate the slope and decay of the IOS curves. A middle: Time course of the IOS and field response A right: Correlation between the number of diodes containing IOS and the stimulus number (R2 = 0.99). B Top left: Overview of the IOS signal on the 464 element photodiode array. Transparent lines indicate the pyramidal cell layer and the granular cell layer of the dentate gyrus (DG). The position of the stimulating electrode is marked by an arrow and the sites of field potential recording electrodes are indicated by colored elipses. B Bottom left: 3D representation of the IOS amplitude. The position of the stimulating and recording electrodes are marked by an arrow and an asteriks, respectively. The colorbar indicates the transmittance change compared to the resting light intensity. B Right: Representative IOS and field response traces recorded at different locations of the slice. The exact location of the traces are indicated by the coloured elipses on the Top Left image. C Left and Middle: 3D IOS amplitude maps before (left) and after (middle) making a cut between the stimulating electrode and CA3. Transparent line indicates the pyramidal layer. The position of the stimulating electrode is marked by an arrow and the site of field potential recording is indicated by an asterisk. C Right: Representative IOS traces near the recording electrode (marked by white asterisk) before (black) and after (red) making a cut between the stimulating electrode and CA3. The slight difference between the curves is due to the slightly decreased electrophysiological characteristics after making cut.

Mentions: For IOS measurements we used a 464 element photodiode-array (PDA) detector instead of the commonly applied charge-coupled device (CCD) camera. The PDA detector enables IOS detection with 0.6 ms time resolution, making it achievable to align the optical signal with the simultaneously measured electrophysiological recordings. To quantify the effect of the applied inhibitors, we calculated six different parameters for each IOS curves: amplitude, location of the maxima, length, 10–90 slope, 90-10 decay and the number of diodes showing significant IOS activity (Figure 1A, B). Amplitude of the IOS signal in the close vicinity of the electrophysiological recording site as well as summa amplitude measured on all diodes covering the entire hippocampus were compared to electrophysiological signal parameters, namely the amplitude of the population spike (PS) and the slope of the field excitatory postsynaptic potential (fEPSP). The amplitude of the population spike measures the synchronous firing of the neighboring neurons [33], while the slope of the fEPSP measures the currents generated by the synaptic activation of pyramidal cells [34].


Neuronal and astroglial correlates underlying spatiotemporal intrinsic optical signal in the rat hippocampal slice.

Pál I, Nyitrai G, Kardos J, Héja L - PLoS ONE (2013)

Time course, stimulation dependency and regional distribution of IOS and field response.A left: Changes of IOS shape and amplitude with the increasing number of stimuli. Numbers above that curves indicate the stimulus number. Transparent lines show the fitted linear function to calculate the slope and decay of the IOS curves. A middle: Time course of the IOS and field response A right: Correlation between the number of diodes containing IOS and the stimulus number (R2 = 0.99). B Top left: Overview of the IOS signal on the 464 element photodiode array. Transparent lines indicate the pyramidal cell layer and the granular cell layer of the dentate gyrus (DG). The position of the stimulating electrode is marked by an arrow and the sites of field potential recording electrodes are indicated by colored elipses. B Bottom left: 3D representation of the IOS amplitude. The position of the stimulating and recording electrodes are marked by an arrow and an asteriks, respectively. The colorbar indicates the transmittance change compared to the resting light intensity. B Right: Representative IOS and field response traces recorded at different locations of the slice. The exact location of the traces are indicated by the coloured elipses on the Top Left image. C Left and Middle: 3D IOS amplitude maps before (left) and after (middle) making a cut between the stimulating electrode and CA3. Transparent line indicates the pyramidal layer. The position of the stimulating electrode is marked by an arrow and the site of field potential recording is indicated by an asterisk. C Right: Representative IOS traces near the recording electrode (marked by white asterisk) before (black) and after (red) making a cut between the stimulating electrode and CA3. The slight difference between the curves is due to the slightly decreased electrophysiological characteristics after making cut.
© Copyright Policy
Related In: Results  -  Collection

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getmorefigures.php?uid=PMC3585794&req=5

pone-0057694-g001: Time course, stimulation dependency and regional distribution of IOS and field response.A left: Changes of IOS shape and amplitude with the increasing number of stimuli. Numbers above that curves indicate the stimulus number. Transparent lines show the fitted linear function to calculate the slope and decay of the IOS curves. A middle: Time course of the IOS and field response A right: Correlation between the number of diodes containing IOS and the stimulus number (R2 = 0.99). B Top left: Overview of the IOS signal on the 464 element photodiode array. Transparent lines indicate the pyramidal cell layer and the granular cell layer of the dentate gyrus (DG). The position of the stimulating electrode is marked by an arrow and the sites of field potential recording electrodes are indicated by colored elipses. B Bottom left: 3D representation of the IOS amplitude. The position of the stimulating and recording electrodes are marked by an arrow and an asteriks, respectively. The colorbar indicates the transmittance change compared to the resting light intensity. B Right: Representative IOS and field response traces recorded at different locations of the slice. The exact location of the traces are indicated by the coloured elipses on the Top Left image. C Left and Middle: 3D IOS amplitude maps before (left) and after (middle) making a cut between the stimulating electrode and CA3. Transparent line indicates the pyramidal layer. The position of the stimulating electrode is marked by an arrow and the site of field potential recording is indicated by an asterisk. C Right: Representative IOS traces near the recording electrode (marked by white asterisk) before (black) and after (red) making a cut between the stimulating electrode and CA3. The slight difference between the curves is due to the slightly decreased electrophysiological characteristics after making cut.
Mentions: For IOS measurements we used a 464 element photodiode-array (PDA) detector instead of the commonly applied charge-coupled device (CCD) camera. The PDA detector enables IOS detection with 0.6 ms time resolution, making it achievable to align the optical signal with the simultaneously measured electrophysiological recordings. To quantify the effect of the applied inhibitors, we calculated six different parameters for each IOS curves: amplitude, location of the maxima, length, 10–90 slope, 90-10 decay and the number of diodes showing significant IOS activity (Figure 1A, B). Amplitude of the IOS signal in the close vicinity of the electrophysiological recording site as well as summa amplitude measured on all diodes covering the entire hippocampus were compared to electrophysiological signal parameters, namely the amplitude of the population spike (PS) and the slope of the field excitatory postsynaptic potential (fEPSP). The amplitude of the population spike measures the synchronous firing of the neighboring neurons [33], while the slope of the fEPSP measures the currents generated by the synaptic activation of pyramidal cells [34].

Bottom Line: It was eliminated by tetrodotoxin blockade of voltage-gated Na(+) channels and was significantly enhanced by suppressing inhibitory signaling with gamma-aminobutyric acid(A) receptor antagonist picrotoxin.We found that IOS was predominantly initiated by postsynaptic Glu receptor activation and progressed by the activation of astroglial Glu transporters and Mg(2+)-independent astroglial N-methyl-D-aspartate receptors.Our model may help to better interpret in vivo IOS and support diagnosis in the future.

View Article: PubMed Central - PubMed

Affiliation: Department of Functional Pharmacology, Institute of Molecular Pharmacology, Research Centre for Natural Sciences, Hungarian Academy of Sciences, Budapest, Hungary. pal.ildiko@ttk.mta.hu

ABSTRACT
Widely used for mapping afferent activated brain areas in vivo, the label-free intrinsic optical signal (IOS) is mainly ascribed to blood volume changes subsequent to glial glutamate uptake. By contrast, IOS imaged in vitro is generally attributed to neuronal and glial cell swelling, however the relative contribution of different cell types and molecular players remained largely unknown. We characterized IOS to Schaffer collateral stimulation in the rat hippocampal slice using a 464-element photodiode-array device that enables IOS monitoring at 0.6 ms time-resolution in combination with simultaneous field potential recordings. We used brief half-maximal stimuli by applying a medium intensity 50 Volt-stimulus train within 50 ms (20 Hz). IOS was primarily observed in the str. pyramidale and proximal region of the str. radiatum of the hippocampus. It was eliminated by tetrodotoxin blockade of voltage-gated Na(+) channels and was significantly enhanced by suppressing inhibitory signaling with gamma-aminobutyric acid(A) receptor antagonist picrotoxin. We found that IOS was predominantly initiated by postsynaptic Glu receptor activation and progressed by the activation of astroglial Glu transporters and Mg(2+)-independent astroglial N-methyl-D-aspartate receptors. Under control conditions, role for neuronal K(+)/Cl(-) cotransporter KCC2, but not for glial Na(+)/K(+)/Cl(-) cotransporter NKCC1 was observed. Slight enhancement and inhibition of IOS through non-specific Cl(-) and volume-regulated anion channels, respectively, were also depicted. High-frequency IOS imaging, evoked by brief afferent stimulation in brain slices provide a new paradigm for studying mechanisms underlying IOS genesis. Major players disclosed this way imply that spatiotemporal IOS reflects glutamatergic neuronal activation and astroglial response, as observed within the hippocampus. Our model may help to better interpret in vivo IOS and support diagnosis in the future.

Show MeSH
Related in: MedlinePlus