Limits...
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.

Show MeSH

Related in: MedlinePlus

Neuronal K+/Cl−cotransporter, non-specific Cl−and volume-regulated anion channels contribute to IOS.A Left and Middle: Representative IOS amplitude map and field response curve under control condition and 5 mM furosemide application, respectively. 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 furosemide application. B Left and Middle: Representative IOS amplitude map and field response curve under control condition and 200 µM DIDS 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 DIDS application. C: The effect of 5 mM furosemide, 10 µM bumetanide, 200 µM DIDS and 40 µM DCPIB 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 = 5−8). 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


getmorefigures.php?uid=PMC3585794&req=5

pone-0057694-g005: Neuronal K+/Cl−cotransporter, non-specific Cl−and volume-regulated anion channels contribute to IOS.A Left and Middle: Representative IOS amplitude map and field response curve under control condition and 5 mM furosemide application, respectively. 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 furosemide application. B Left and Middle: Representative IOS amplitude map and field response curve under control condition and 200 µM DIDS 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 DIDS application. C: The effect of 5 mM furosemide, 10 µM bumetanide, 200 µM DIDS and 40 µM DCPIB 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 = 5−8). 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: KCC2 transports Cl− and K+ ions out of the cells, and is crucial for the maintenance of neuronal intracellular [Cl−] [57]. NKCC1 is mainly expressed on astrocytes and transports Na+, K+ and Cl− ions into the cell [42]. The precise balance between the activities of the two transporters is needed to maintain inhibitory GABAergic signaling in the adult central nervous system [58]. NKCC1 has been suggested to play a decisive role in stimulus evoked IOS due to the dramatic decrease of IOS after application of furosemide [7], [19]. In our experiments furosemide (5 mM), the inhibitor of both NKCC1 and KCC2 in the first 5 min of application increased PS amplitude by 226±37% of control while decreased the fEPSP slope by 17±8% of control. The increased neuronal excitability may be due to the impaired GABAA receptor mediated inhibitory function [59] or the reduced K+ driving force [60]. In contrast to the PS amplitude, summa IOS amplitude was decreased (by 37±9% of control, N = 8, Figure 5A and C), most prominently in the str. radiatum (Figure 5A). It is to note that the IOS decay was more significantly affected (by 33±8% of control) than the slope (by 14±7% of control), suggesting that furosemide is acting on the IOS termination process.


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)

Neuronal K+/Cl−cotransporter, non-specific Cl−and volume-regulated anion channels contribute to IOS.A Left and Middle: Representative IOS amplitude map and field response curve under control condition and 5 mM furosemide application, respectively. 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 furosemide application. B Left and Middle: Representative IOS amplitude map and field response curve under control condition and 200 µM DIDS 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 DIDS application. C: The effect of 5 mM furosemide, 10 µM bumetanide, 200 µM DIDS and 40 µM DCPIB 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 = 5−8). 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-g005: Neuronal K+/Cl−cotransporter, non-specific Cl−and volume-regulated anion channels contribute to IOS.A Left and Middle: Representative IOS amplitude map and field response curve under control condition and 5 mM furosemide application, respectively. 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 furosemide application. B Left and Middle: Representative IOS amplitude map and field response curve under control condition and 200 µM DIDS 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 DIDS application. C: The effect of 5 mM furosemide, 10 µM bumetanide, 200 µM DIDS and 40 µM DCPIB 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 = 5−8). 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: KCC2 transports Cl− and K+ ions out of the cells, and is crucial for the maintenance of neuronal intracellular [Cl−] [57]. NKCC1 is mainly expressed on astrocytes and transports Na+, K+ and Cl− ions into the cell [42]. The precise balance between the activities of the two transporters is needed to maintain inhibitory GABAergic signaling in the adult central nervous system [58]. NKCC1 has been suggested to play a decisive role in stimulus evoked IOS due to the dramatic decrease of IOS after application of furosemide [7], [19]. In our experiments furosemide (5 mM), the inhibitor of both NKCC1 and KCC2 in the first 5 min of application increased PS amplitude by 226±37% of control while decreased the fEPSP slope by 17±8% of control. The increased neuronal excitability may be due to the impaired GABAA receptor mediated inhibitory function [59] or the reduced K+ driving force [60]. In contrast to the PS amplitude, summa IOS amplitude was decreased (by 37±9% of control, N = 8, Figure 5A and C), most prominently in the str. radiatum (Figure 5A). It is to note that the IOS decay was more significantly affected (by 33±8% of control) than the slope (by 14±7% of control), suggesting that furosemide is acting on the IOS termination process.

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