Name: Author Spotlight: Deciphering Neural Circuit Formation from Two-Photon Microscopy and Single Neuron Imaging
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This work was supported by the Japan Society for the Promotion of Science Grants-in-Aid for Transformative Research Areas (B) (22H05092, 22H05094) and for Scientific Research Grants 20K06876, AMED under Grant Number 21wm0525015, the Takeda Science Foundation, the Naito Foundation, the Kato Memorial Bioscience Foundation, the Kowa Life Science Foundation, NIG-JOINT (24A2021) (to H.M.); and Japan Society for the Promotion of Science Grants-in-Aid for Scientific Research Grants 19K06887 and 22K06446, the Kodama Memorial Fund for Medical Research, the Uehara Memorial Foundation, the Kato Memorial Bioscience Foundation, and the Takeda Science Foundation (to N.N-T.). We thank Dr. Takuji Iwasato for the TCA-RFP mice.

All the experiments were conducted in accordance with the guidelines for animal experimentation of Kumamoto University and the National Institute of Genetics and approved by the animal experimentation committees.
1. In utero electroporation (IUE)
<ol>
	<li>Mate male TCA-RFP mice of ICR background with female wild-type ICR mice. Observe the vaginal plug to check for mating early morning of the next day. Observe the abdomen to check for pregnancy 2 weeks later.</li>
	...

Neuronal Activity Mapping in Developing Mouse Sensory Cortex

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Given that the spontaneous activities emerge from the sensory organ or lower nervous system and travel to the primary sensory area through a pathway equivalent to that of a mature nervous system3, it is crucial to define the primary sensory area and the location of imaged neurons within the area. In this protocol, we addressed this requirement by employing transgenic mice that visualize thalamocortical axons and the Supernova system that expresses GCaMP sparsely8. These tec...

The cerebral cortex contains several sensory areas with distinct functions. The areas receive inputs originating from their corresponding sensory organs, mostly conveyed through the spinal cord or brainstem and relayed via the thalamus1,2. Notably, neurons in each primary sensory area exhibit uniquely synchronized activity during early developmental stages, which also originate from sensory organs or the lower nervous centers, but essentially differ from the activities observed in the mature cortex3.
In neonatal rodents, for example, the primary visual area (V1) displays wave-like activity, which originates in the retina (retinal wave) and propagates through the entire visual pathway while conserving retinotopy4. The primary auditory area (A1) exhibits synchronous activity organized in band-shaped subregions that correspond to the isofrequency bands in the mature brain. The activity emanates from the cochlea&#39;s inner hair cells5,6. The barrel cortex in the primary somatosensory area (S1) shows a patchwork-like activity pattern in which layer 4 neurons within individual barrels, namely, neurons responsive to individual whiskers, are synchronously activated7. Although proposed to originate from the trigeminal ganglion, the source of the activity remains unknown7. Consequently, neonatal activity patterns are specialized both within each primary sensory area and within intra-areal subfields. The simultaneous visualization of neuronal activity and structure of primary sensory areas may facilitate an inquiry into the contribution of these activity patterns to the development of sensory systems.
In this article, we summarized a series of protocols: (1) to visualize individual neuronal activities using sparse labeling of GCaMP and primary sensory areas using TCA-RFP mice that express red fluorescent protein in thalamocortical axons7, (2) to image single cell-level activity in neonatal mice using two-photon microscopy in vivo, and (3) to analyze the activity correlations within S1 barrel cortex. The representative results show patchwork-like synchronized activity within individual barrels of a postnatal day (P)6 mouse. Despite some limitations, this technique can be used for chronic imaging, wide-field imaging across multiple sensory areas, and various manipulation experiments. The multifaceted analysis of neuronal activity during development will enrich our comprehension of brain circuit formation mechanisms.

<table border="1" fo:keep-together.within-page="1" fo:keep-with-next.within-page="always">
	<tbody>
		<tr>
			<td>20&#215; objective lens (water immersion)</td>
			<td></td>
			<td></td>
			<td></td>
		</tr>
		<tr>
			<td>250 mL Vacuum Filter/Storage Bottle System</td>
			<td>Corning</td>
			<td>431096</td>
			<td></td>
		</tr>
		<tr>
			<td>4%-paraformaldehyde phosphate buffer solution (4% PFA)</td>
			<td>Nacalai</td>
			<td>09154-85</td>
			<td></td>
		</tr>
		<tr>
			<td>Acrylic resin (UNIFAST II)</td>
			<td>GC</td>
			<td>N/A</td>
			<td></td>
		</tr>
		<tr>
			<td>Agarose</td>
			<td>Sigma</td>
			<td>A9793</td>
			<td></td>
		</tr>
		<tr>
			<td>Aspirator tube assembly</td>
			<td>Drummond</td>
			<td>2-040-000</td>
			<td></td>
		</tr>
		<tr>
			<td>CaCl2&#8226;2H2O</td>
			<td>Nacalai</td>
			<td>06731-05</td>
			<td></td>
		</tr>
		<tr>
			<td>Electroporator</td>
			<td>BEX</td>
			<td>GEB14</td>
			<td></td>
		</tr>
		<tr>
			<td>Eye drop (Scopisol)</td>
			<td>Senju Pharmaceutical</td>
			<td>N/A</td>
			<td></td>
		</tr>
		<tr>
			<td>Fluorescence stereo microscope</td>
			<td>Leica</td>
			<td>M165FC</td>
			<td></td>
		</tr>
		<tr>
			<td>Glucose</td>
			<td>Nacalai</td>
			<td>16806-25</td>
			<td></td>
		</tr>
		<tr>
			<td>Heating pad</td>
			<td>Muromachi Kikai</td>
			<td>FHC-HPS</td>
			<td></td>
		</tr>
		<tr>
			<td>HEPES</td>
			<td>Gibco</td>
			<td>15630-080</td>
			<td></td>
		</tr>
		<tr>
			<td>Isoflurane</td>
			<td>Pfizer</td>
			<td>N/A</td>
			<td></td>
		</tr>
		<tr>
			<td>KCl</td>
			<td>Nacalai</td>
			<td>28514-75</td>
			<td></td>
		</tr>
		<tr>
			<td>MgSO4&#8226;7H2O</td>
			<td>Wako</td>
			<td>131-00405</td>
			<td></td>
		</tr>
		<tr>
			<td>Micropipette puller</td>
			<td>Narishige</td>
			<td>PC-100</td>
			<td></td>
		</tr>
		<tr>
			<td>Multiphoton laser</td>
			<td>Spectra-Physics</td>
			<td>Mai Tai eHP DeepSee</td>
			<td></td>
		</tr>
		<tr>
			<td>Multiphoton microscope</td>
			<td>Zeiss</td>
			<td>LSM 7MP</td>
			<td></td>
		</tr>
		<tr>
			<td>NaCl</td>
			<td>Nacalai</td>
			<td>31320-05</td>
			<td></td>
		</tr>
		<tr>
			<td>Non-woven fabric (Kimwipe)</td>
			<td>Kimberly Clark</td>
			<td>S-200</td>
			<td></td>
		</tr>
		<tr>
			<td>Phosphate buffered saline (PBS)</td>
			<td>Nacalai</td>
			<td>27575-31</td>
			<td></td>
		</tr>
		<tr>
			<td>Plasmid: CAG-loxP-STOP-loxP-GCaMP6s-ires-tTA-WPRE</td>
			<td>Addgene</td>
			<td>pK175</td>
			<td></td>
		</tr>
		<tr>
			<td>Plasmid: TRE-nCre</td>
			<td>Addgene</td>
			<td>pK031</td>
			<td></td>
		</tr>
		<tr>
			<td>Precision calibrated micropipets</td>
			<td>Drummond</td>
			<td>2-000-050</td>
			<td></td>
		</tr>
		<tr>
			<td>Razor blade</td>
			<td>Feather</td>
			<td>FA-10</td>
			<td></td>
		</tr>
		<tr>
			<td>Rimadyl (50 mg/mL Carprofen)</td>
			<td>Zoetis JP</td>
			<td>N/A</td>
			<td></td>
		</tr>
		<tr>
			<td>Round cover glass, 3-mm-diameter&#160;</td>
			<td>Matsunami</td>
			<td>CS01078</td>
			<td></td>
		</tr>
		<tr>
			<td>Saline</td>
			<td>Otsuka</td>
			<td>035175315</td>
			<td></td>
		</tr>
		<tr>
			<td>Sodium pentobarbital</td>
			<td>Nacalai</td>
			<td>26427-72</td>
			<td></td>
		</tr>
		<tr>
			<td>Stage for imaging living pup (two single-axis translation stage for XY positioning, two-axis goniometer, base plate, adjustable pillar for z positioning)</td>
			<td>ThorLabs</td>
			<td>LT1/M, GN2/M, BM2060/M, MLP01/M</td>
			<td></td>
		</tr>
		<tr>
			<td>TCA-RFP mouse</td>
			<td>N/A</td>
			<td>N/A</td>
			<td>Mizuno et al., 2018a</td>
		</tr>
		<tr>
			<td>Tissue adhesive (Vetbond)</td>
			<td>3M</td>
			<td>1469SB</td>
			<td></td>
		</tr>
		<tr>
			<td>Titanium bar</td>
			<td>Endo Scientific Instrument</td>
			<td>N/A</td>
			<td>Custom made (Mizuno et al., 2018b)</td>
		</tr>
		<tr>
			<td>Titanium bar fixing plate</td>
			<td></td>
			<td>N/A</td>
			<td>Custom made (Mizuno et al., 2018b)</td>
		</tr>
		<tr>
			<td>Trypan blue</td>
			<td>Sigma</td>
			<td>T8154</td>
			<td></td>
		</tr>
		<tr>
			<td>Tweezers with platinum plate electrode, 5 mm diameter</td>
			<td>BEX</td>
			<td>CUY650P5</td>
			<td></td>
		</tr>
		<tr>
			<td>Wild-type ICR mouse</td>
			<td>Nihon SLC</td>
			<td>Slc:ICR</td>
			<td></td>
		</tr>
	</tbody>
</table>

in vivo visualization of spontaneous activity in neonatal mouse sensory cortex at a single-neuron resolution

The mammalian brain undergoes dynamic developmental changes at both the cellular and circuit levels throughout prenatal and postnatal periods. Following the discovery of numerous genes contributing to these developmental changes, it is now known that neuronal activity also substantially modulates these processes. In the developing cerebral cortex, neurons exhibit synchronized activity patterns that are specialized to each primary sensory area. These patterns markedly differ from those observed in the mature cortex, emphasizing their role in regulating area-specific developmental processes. Deficiencies in neuronal activity during development can lead to various brain diseases. These findings highlight the need to examine the regulatory mechanisms underlying activity patterns in neuronal development. This paper summarizes a series of protocols to visualize primary sensory areas and neuronal activity in neonatal mice, to image the activity of individual neurons within the cortical subfields using two-photon microscopy in vivo, and to analyze subfield-related activity correlations. We show representative results of patchwork-like synchronous activity within individual barrels in the somatosensory cortex. We also discuss various potential applications and some limitations of this protocol.

Author Spotlight: Deciphering Neural Circuit Formation from Two-Photon Microscopy and Single Neuron Imaging

In Vivo Visualization of Spontaneous Activity in Neonatal Mouse Sensory Cortex at a Single-Neuron Resolution

The purpose of our research is to investigate the formation of neural circuits in the developing cerebral cortex. We aim to understand the role of neuronal activity in this process. In recent years, two-photon microscopy has made it possible to observe the process of neuronal circuit formation in living animals.We have developed a method for imaging single neurons in the neonatal cerebral cortex. By simultaneously observing activity patterns and changes in their morphology, we will be able to clarify which activity patterns are involved in neuronal circuit formation.

Figure 1 shows the representative results of layer 4 neuron activities in the barrel cortex of a P6 pup visualized using the present protocol. Two-photon images of the green channel (GCaMP) and red channel (TCA-RFP) were temporally averaged and shown in Figure 1A. Because TCA-RFP fluorescence was much weaker than GCaMP fluorescence, the GCaMP signal leaked into the red channel (Figure 1A1,A2). Fourteen ROIs were dra...

Read this Scientific Article Protocol about Author Spotlight: Deciphering Neural Circuit Formation from Two-Photon Microscopy and Single Neuron Imaging at JoVE.com

Primary sensory areas in the neocortex exhibit unique spontaneous activities during development. This article describes how to visualize individual neuron activities and primary sensory areas to analyze area-specific synchronous activities in neonatal mice in vivo.

The mammalian brain undergoes dynamic developmental changes at both the cellular and circuit levels throughout prenatal and postnatal periods. Following ...