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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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IOS amplitude is directly dependent on neural activity.A Left and Middle: Representative IOS amplitude map and field response curve under control condition and 5 µM TTX application. The colorbar indicates the maximum change of the transmittance compared to the resting light intensity. A Right: Spatial visualization of the percentage of control changes of IOS signal caused by TTX application. B Left and Middle: Representative IOS amplitude map and field response curve under control condition and 100 µM picrotoxin application, respectively. The colorbar indicates the maximum change of the transmittance compared to the resting light intensity. B Right: Spatial visualization of the percentage of control changes of IOS signal caused by 100 µM picrotoxin application. C: The effect of 100 µM picrotoxin and 5 µM TTX on the field response and IOS parameters in percentage of control. Asterisks indicate significant changes compared to control (P<0.05 Mann-Whitney U test, N = 5). Transparent lines on panel A, B right indicate the pyramidal cell layer. The position of the stimulating and recording electrode are marked by an arrow and asteriks, respectively.
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pone-0057694-g003: IOS amplitude is directly dependent on neural activity.A Left and Middle: Representative IOS amplitude map and field response curve under control condition and 5 µM TTX application. The colorbar indicates the maximum change of the transmittance compared to the resting light intensity. A Right: Spatial visualization of the percentage of control changes of IOS signal caused by TTX application. B Left and Middle: Representative IOS amplitude map and field response curve under control condition and 100 µM picrotoxin application, respectively. The colorbar indicates the maximum change of the transmittance compared to the resting light intensity. B Right: Spatial visualization of the percentage of control changes of IOS signal caused by 100 µM picrotoxin application. C: The effect of 100 µM picrotoxin and 5 µM TTX on the field response and IOS parameters in percentage of control. Asterisks indicate significant changes compared to control (P<0.05 Mann-Whitney U test, N = 5). Transparent lines on panel A, B right indicate the pyramidal cell layer. The position of the stimulating and recording electrode are marked by an arrow and asteriks, respectively.

Mentions: Blockade of voltage-gated sodium channels by TTX (5 µM) completely eliminated both the field response (PS amplitude and fEPSP slope: 0±3 and 0±0% of control, respectively; N = 5) and IOS (IOS sum. ampl.: 0±1% of control, N = 5). IOS completely disappeared from all cell layers (Figure 3A), demonstrating that the passive voltage propagation in the tissue is insufficient to evoke IOS, therefore neuronal activation is necessary for IOS generation.


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)

IOS amplitude is directly dependent on neural activity.A Left and Middle: Representative IOS amplitude map and field response curve under control condition and 5 µM TTX application. The colorbar indicates the maximum change of the transmittance compared to the resting light intensity. A Right: Spatial visualization of the percentage of control changes of IOS signal caused by TTX application. B Left and Middle: Representative IOS amplitude map and field response curve under control condition and 100 µM picrotoxin application, respectively. The colorbar indicates the maximum change of the transmittance compared to the resting light intensity. B Right: Spatial visualization of the percentage of control changes of IOS signal caused by 100 µM picrotoxin application. C: The effect of 100 µM picrotoxin and 5 µM TTX on the field response and IOS parameters in percentage of control. Asterisks indicate significant changes compared to control (P<0.05 Mann-Whitney U test, N = 5). Transparent lines on panel A, B right indicate the pyramidal cell layer. The position of the stimulating and recording electrode are marked by an arrow and asteriks, respectively.
© Copyright Policy
Related In: Results  -  Collection

Show All Figures
getmorefigures.php?uid=PMC3585794&req=5

pone-0057694-g003: IOS amplitude is directly dependent on neural activity.A Left and Middle: Representative IOS amplitude map and field response curve under control condition and 5 µM TTX application. The colorbar indicates the maximum change of the transmittance compared to the resting light intensity. A Right: Spatial visualization of the percentage of control changes of IOS signal caused by TTX application. B Left and Middle: Representative IOS amplitude map and field response curve under control condition and 100 µM picrotoxin application, respectively. The colorbar indicates the maximum change of the transmittance compared to the resting light intensity. B Right: Spatial visualization of the percentage of control changes of IOS signal caused by 100 µM picrotoxin application. C: The effect of 100 µM picrotoxin and 5 µM TTX on the field response and IOS parameters in percentage of control. Asterisks indicate significant changes compared to control (P<0.05 Mann-Whitney U test, N = 5). Transparent lines on panel A, B right indicate the pyramidal cell layer. The position of the stimulating and recording electrode are marked by an arrow and asteriks, respectively.
Mentions: Blockade of voltage-gated sodium channels by TTX (5 µM) completely eliminated both the field response (PS amplitude and fEPSP slope: 0±3 and 0±0% of control, respectively; N = 5) and IOS (IOS sum. ampl.: 0±1% of control, N = 5). IOS completely disappeared from all cell layers (Figure 3A), demonstrating that the passive voltage propagation in the tissue is insufficient to evoke IOS, therefore neuronal activation is necessary for IOS generation.

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