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A neuronal MCT2 knockdown in the rat somatosensory cortex reduces both the NMR lactate signal and the BOLD response during whisker stimulation

View Article: PubMed Central - PubMed

ABSTRACT

Although several in vitro and ex vivo evidence support the existence of lactate exchange between astrocytes and neurons, a direct demonstration in vivo is still lacking. In the present study, a lentiviral vector carrying a short hairpin RNA (shRNA) was used to downregulate the expression of the monocarboxylate transporter type 2 (MCT2) in neurons of the rat somatosensory cortex (called S1BF) by ~ 25%. After one hour of whisker stimulation, HRMAS 1H-NMR spectroscopy analysis of S1BF perchloric acid extracts showed that while an increase in lactate content is observed in both uninjected and shRNA-control injected extracts, such an effect was abrogated in shMCT2 injected rats. A 13C-incorporation analysis following [1-13C]glucose infusion during the stimulation confirmed that the elevated lactate observed during activation originates from newly synthesized [3-13C]lactate, with blood-derived [1-13C]glucose being the precursor. Moreover, the analysis of the 13C-labeling of glutamate in position C3 and C4 indicates that upon activation, there is an increase in TCA cycle velocity for control rats while a decrease is observed for MCT2 knockdown animals. Using in vivo localized 1H-NMR spectroscopy, an increase in lactate levels is observed in the S1BF area upon whisker stimulation for shRNA-control injected rats but not for MCT2 knockdown animals. Finally, while a robust BOLD fMRI response was evidenced in control rats, it was absent in MCT2 knockdown rats. These data not only demonstrate that glucose-derived lactate is locally produced following neuronal activation but also suggest that its use by neurons via MCT2 is probably essential to maintain synaptic activity within the barrel cortex.

No MeSH data available.


BOLD-fMRI of the S1BF areas of control rats (A, n = 4) and MCT2 rats (B, n = 4) during right whisker activation. Images shown represent one typical experiment. Quantifications of the 4 experiments are presented in the tables. The red square represents the location of the voxel (present on 3 slices) in which the in vivo spectroscopy was performed and the number of activated pixel was counted in both red (activated S1BF) and blue (rest S1BF) voxels.
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pone.0174990.g006: BOLD-fMRI of the S1BF areas of control rats (A, n = 4) and MCT2 rats (B, n = 4) during right whisker activation. Images shown represent one typical experiment. Quantifications of the 4 experiments are presented in the tables. The red square represents the location of the voxel (present on 3 slices) in which the in vivo spectroscopy was performed and the number of activated pixel was counted in both red (activated S1BF) and blue (rest S1BF) voxels.

Mentions: Finally, BOLD fMRI was performed on stimulated animals (Fig 6). In control rats, the right whisker stimulation led to a BOLD signal in the left barrel cortex. Surprisingly, this signal was no more visible in MCT2 rats.


A neuronal MCT2 knockdown in the rat somatosensory cortex reduces both the NMR lactate signal and the BOLD response during whisker stimulation
BOLD-fMRI of the S1BF areas of control rats (A, n = 4) and MCT2 rats (B, n = 4) during right whisker activation. Images shown represent one typical experiment. Quantifications of the 4 experiments are presented in the tables. The red square represents the location of the voxel (present on 3 slices) in which the in vivo spectroscopy was performed and the number of activated pixel was counted in both red (activated S1BF) and blue (rest S1BF) voxels.
© Copyright Policy
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC5384673&req=5

pone.0174990.g006: BOLD-fMRI of the S1BF areas of control rats (A, n = 4) and MCT2 rats (B, n = 4) during right whisker activation. Images shown represent one typical experiment. Quantifications of the 4 experiments are presented in the tables. The red square represents the location of the voxel (present on 3 slices) in which the in vivo spectroscopy was performed and the number of activated pixel was counted in both red (activated S1BF) and blue (rest S1BF) voxels.
Mentions: Finally, BOLD fMRI was performed on stimulated animals (Fig 6). In control rats, the right whisker stimulation led to a BOLD signal in the left barrel cortex. Surprisingly, this signal was no more visible in MCT2 rats.

View Article: PubMed Central - PubMed

ABSTRACT

Although several in vitro and ex vivo evidence support the existence of lactate exchange between astrocytes and neurons, a direct demonstration in vivo is still lacking. In the present study, a lentiviral vector carrying a short hairpin RNA (shRNA) was used to downregulate the expression of the monocarboxylate transporter type 2 (MCT2) in neurons of the rat somatosensory cortex (called S1BF) by ~ 25%. After one hour of whisker stimulation, HRMAS 1H-NMR spectroscopy analysis of S1BF perchloric acid extracts showed that while an increase in lactate content is observed in both uninjected and shRNA-control injected extracts, such an effect was abrogated in shMCT2 injected rats. A 13C-incorporation analysis following [1-13C]glucose infusion during the stimulation confirmed that the elevated lactate observed during activation originates from newly synthesized [3-13C]lactate, with blood-derived [1-13C]glucose being the precursor. Moreover, the analysis of the 13C-labeling of glutamate in position C3 and C4 indicates that upon activation, there is an increase in TCA cycle velocity for control rats while a decrease is observed for MCT2 knockdown animals. Using in vivo localized 1H-NMR spectroscopy, an increase in lactate levels is observed in the S1BF area upon whisker stimulation for shRNA-control injected rats but not for MCT2 knockdown animals. Finally, while a robust BOLD fMRI response was evidenced in control rats, it was absent in MCT2 knockdown rats. These data not only demonstrate that glucose-derived lactate is locally produced following neuronal activation but also suggest that its use by neurons via MCT2 is probably essential to maintain synaptic activity within the barrel cortex.

No MeSH data available.