Transcranial imaging of intracellular Ca2+ in astrocytes and neurons

RIKEN BRC August 2017
Mouse of the Month


Transcranial imaging of intracellular Ca2+ in astrocytes and neurons

C57BL/6-Tg(Slc1a2-G-CaMP7)Bsi (RBRC09650)

Transcranial direct current stimulation (tDCS) is a non-invasive treatment, in which weak direct current is applied through the skull. tDCS has been known to ameliorate neuropsychiatric and neurological conditions in humans. Although membrane potential fluctuations of astrocytes, the major glia cell type in the brain, are within a few millivolts from resting potential, recent reports have raised the possibility that intracellular Ca2+ elevation in astrocytes results in gliotransmission. Hirase and colleagues sought to reveal cellular mechanism for tDCS-induced plasticity in the mouse brain. They generated the G7NG817 mouse line that expresses G-CaMP7, the improved variant of genetically encoded calcium indicator G-CaMP [1], under a GLT-1 (or Slc1a2). The G7NG817 mouse was found to express high levels of G-CaMP7 in astrocytes and a subpopulation of neurons in the forebrain including the cortex and hippocampus, allowing transcranial Ca2+ imaging with a standard fluorescence microscope. Using G7NG817 mice, they showed that tDCS results in an enhancement of sensory evoked cortical response via astrocytic Ca2+ surges mediated by alpha-1 adrenergic receptor signaling [2, 3]. Recently, G7NG817 mice were used to characterize the in vivo functional dynamics of the somatosensory cortex in autistic mice [4], demonstrating the versatility of this mouse line by cross-breeding with various disease model mice.

Depositor : Hajime Hirase, Ph.D.
Laboratory for Neuron-Glia Circuitry
RIKEN Brain Science Institute
Strain name : C57BL/6-Tg(Slc1a2-G-CaMP7)Bsi
RBRC No. : RBRC09650
References : [1] Ohkura M, Sasaki T, Sadakari J, Gengyo-Ando K, Kagawa-Nagamura Y, Kobayashi C, Ikegaya Y, Nakai J. Genetically encoded green fluorescent Ca2+ indicators with improved detectability for neuronal Ca2+ signals. PLOS ONE; 7(12):e51286, 2012.
[2] Monai H, Ohkura M, Tanaka M, Oe Y, Konno A, Hirai H, Mikoshiba K, Itohara S, Nakai J, Iwai Y, Hirase H. Calcium imaging reveals glial involvement in transcranial direct current stimulation-induced plasticity in mouse brain. Nat Commun.; 7:11100, 2016.
[3] Monai H, Hirase H. Astrocytic calcium activation in a mouse model of tDCS-Extended discussion. Neurogenesis (Austin); 3(1):e1240055, 2016.
[4] Nakai N, Nagano M, Saitow F, Watanabe Y, Kawamura Y, Kawamoto A, Tamada K, Mizuma H, Onoe H, Watanabe Y, Monai H, Hirase H, Nakatani J, Inagaki H, Kawada T, Miyazaki T, Watanabe M, Sato Y, Okabe S, Kitamura K, Kano M, Hashimoto K, Suzuki H, Takumi T. Serotonin rebalances cortical tuning and behavior linked to autism symptoms in 15q11-13 CNV mice. Sci Adv; 3(6):e1603001, 2017



Sagittal brain section of the G7NG817 (upper panel) and C57BL/6 wild type mice (lower panel). High expression of G-CaMP7 was seen in the cortex, hippocampus (particularly CA3), thalamus, and striatum. Scale bar: 1 mm.



Transcranial imaging of the slow oscillations during deep anesthesia in G7NG817
Transcranial imaging on a urethane anesthetized G7NG817 mouse displays large-amplitude and synchronized slow oscillations (A). The normalized fluorescence intensity (ΔF/F) from the visual cortex (A, black square) is plotted in B. The frequency of the oscillations ranges from 0.5 to 2 Hz, consistent with the LFP slow oscillations reported in urethane-anesthetized rodents. The images are taken at a frame rate of 10 Hz. The dotted area in B is magnified in C. The diamond symbols represent the time points for the images displayed in A.



Transcranial functional mapping of the cerebral cortex using G7NG817
A. To demonstrate the utility of G7NG817 for functional mapping, individual whiskers were deflected while transcranial imaging was made over the barrel cortex. The barrel area (yellow square) was imaged while individual whiskers were separately deflected at a frequency of 10 Hz for 5 s in an anesthetized G7NG817 mouse. The mean responses for individual whiskers (16 repetitions) are overlaid in the middle panel. The peak response for D1 whisker stimulation (arrow) is ΔF/F: 3.02 %. The stimulated whiskers and the corresponding barrel structure are shown in the right panel.
B. Functional mapping of other sensory modalities was also demonstrated in awake and head-restraint conditions. For instance, visual flash stimulation (10 ms) presented to either eye resulted in an activation of the contralateral visual cortex (average of 16 responses). The same mouse as in Figure S3A is presented.
C. Visualization of cortical dynamics in response to pure tone presentation (5 kHz pure tone for 500 ms) to an anesthetized mouse. The primary auditory cortex is activated (average of 16 trials).
Scale bars: a, 1 mm, 250 µm.


“Calcium imaging reveals glial involvement in transcranial direct current stimulation-induced plasticity in mouse brain.” Monai H, Ohkura M, Tanaka M, Oe Y, Konno A, Hirai H, Mikoshiba K, Itohara S, Nakai J, Iwai Y, Hirase H.
Nat Commun.; 7:11100, 2016.


August 2017
Contact: Shinya Ayabe, Ph.D.
Experimental Animal Division, RIKEN BioResource Center
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