The authors thank T. Sato, M. Kanbayashi, and S. Kouyama for their technical assistance. This work was supported by JSPS KAKENHI Grant Numbers JP15K14322 and JP16H06143, the Takeda Science Foundation, the Uehara Memorial Foundation, and the Collaborative Research Project of Niigata University Brain Research Institute 2017-2923 (H.M.) and by KAKENHI JP16K14559, JP15H01454, and JP15H04263 and Grant-in Scientific Research on Innovation Areas &#34;Dynamic regulation of Brain Function by Scrap &#38; Build System&#34; (JP16H06459) from MEXT (T.I.).

Experiments should be performed in accordance with the animal welfare guidelines prescribed by the experimenter&#39;s institution.
1. Preparation of Pups for Imaging
NOTE: Pups with sparsely labeled cortical neurons can be obtained by in utero electroporation (IUE) of Supernova vectors5,6. The Supernova system consists of the following two vectors: TRE-Cre and CAG-loxP-STOP-loxP-Gene X-ires-tTA-WPRE. ...

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C., Kubota, M., Ogawa, M., Shimogori, T. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Mouse+in+utero+electroporation:+controlled+spatiotemporal+gene+transfection.">Mouse in utero electroporation: controlled spatiotemporal gene transfection.</a> Journal of Visualized Experiments. (54), e3024 (2011).</li><li>Holtmaat, A., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Long-term,+high-resolution+imaging+in+the+mouse+neocortex+through+a+chronic+cranial+window.">Long-term, high-resolution imaging in the mouse neocortex through a chronic cranial window.</a> Nature Protocols. 4 (8), 1128-1144 (2009).</li><li>Nakai, J., Ohkura, M., Imoto, K. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=A+high+signal-to-noise+Ca(2+)+probe+composed+of+a+single+green+fluorescent+protein.">A high signal-to-noise Ca(2+) probe composed of a single green fluorescent protein.</a> Nature Biotechnology. 19 (2), 137-141 (2001).</li><li>Chen, T. W., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Ultrasensitive+fluorescent+proteins+for+imaging+neuronal+activity.">Ultrasensitive fluorescent proteins for imaging neuronal activity.</a> Nature. 499 (7458), 295-300 (2013).</li><li>Mizuno, H., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Patchwork-Type+Spontaneous+Activity+in+Neonatal+Barrel+Cortex+Layer+4+Transmitted+via+Thalamocortical+Projections.">Patchwork-Type Spontaneous Activity in Neonatal Barrel Cortex Layer 4 Transmitted via Thalamocortical Projections.</a> Cell Reports. 22 (1), 123-135 (2018).</li><li>Zong, H., Espinosa, J. S., Su, H. H., Muzumdar, M. D., Luo, L. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Mosaic+analysis+with+double+markers+in+mice.">Mosaic analysis with double markers in mice.</a> Cell. 121 (3), 479-492 (2005).</li><li>Young, P., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Single-neuron+labeling+with+inducible+Cre-mediated+knockout+in+transgenic+mice.">Single-neuron labeling with inducible Cre-mediated knockout in transgenic mice.</a> Nature Neuroscience. 11 (6), 721-728 (2008).</li><li>Liu, J., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Neonatal+Repeated+Exposure+to+Isoflurane+not+Sevoflurane+in+Mice+Reversibly+Impaired+Spatial+Cognition+at+Juvenile-Age.">Neonatal Repeated Exposure to Isoflurane not Sevoflurane in Mice Reversibly Impaired Spatial Cognition at Juvenile-Age.</a> Neurochemical Research. 42 (2), 595-605 (2017).</li><li>Kondo, M., Kobayashi, K., Ohkura, M., Nakai, J., Matsuzaki, M. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Two-photon+calcium+imaging+of+the+medial+prefrontal+cortex+and+hippocampus+without+cortical+invasion.">Two-photon calcium imaging of the medial prefrontal cortex and hippocampus without cortical invasion.</a> eLIFE. 6, e26839 (2017).</li><li>Nakazawa, S., Mizuno, H., Iwasato, T. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Differential+dynamics+of+cortical+neuron+dendritic+trees+revealed+by+long-term+in+vivo+imaging+in+neonates.">Differential dynamics of cortical neuron dendritic trees revealed by long-term in vivo imaging in neonates.</a> Nature Communications. 9 (1), 3106 (2018).</li></ol>

Critical Steps in the Protocol and Troubleshooting:
The most critical step of the protocol is the removal of the skull (Protocol step 3.2). Upon insertion, the razor blade often adheres to the dura, causing dural bleeding and damage to the brain. This can be avoided by adding a drop of cortex buffer on the skull and removing the skull in cortex buffer.
Bleeding from the dura and the skin after cranial window preparation leads to occlusion of the window. To avoid this, ...

The precise wiring of neuronal circuits in the cerebral cortex is essential for higher brain functions including perception, cognition, and learning and memory. Cortical circuits are dynamically refined during postnatal development. Studies have investigated the process of cortical circuit formation using histological and in vitro culture analyses. However, the dynamics of circuit formation in living mammals has remained mostly unexplored.
Two-photon microscopy has been widely used for the in vivo analyses of neuronal circuits in the adult mouse brain1,2. However, owing to technical challenges, only a limited number of studies have addressed neuronal circuit formation in newborn mice. For example, Carrillo et al. performed the time-lapse imaging of climbing fibers in the cerebellum in the second postnatal week3. Portera-Cailliau et al. reported the imaging of axons in cortical layer 1 in the first postnatal week4. In the present study, we summarize a protocol for the observation of layer 4 cortical neurons and their dendrites in newborn mice. Results obtained by applying this protocol, which includes two methodologies, are reported in our recent publication5. First, we use the Supernova vector system5,6 for labeling individual neurons in the neonatal brain. In the Supernova system, the fluorescent proteins used for neuronal labeling are exchangeable and labeled cell-specific gene knockdown and editing/knockout analyses are also possible. Second, we describe a surgical procedure for cranial window preparation in fragile neonatal mice. Together, these methodologies allow the in vivo observation of individual neurons in neonatal brains.

<table>
	<tbody>
		<tr>
			<td>pK031. TRE-Cre</td>
			<td>Authors</td>
			<td>-</td>
			<td>Available from RIKEN BRC and Addgene</td>
		</tr>
		<tr>
			<td>pK029. CAG-loxP-STOP-loxP-RFP-ires-tTA-WPRE</td>
			<td>Authors</td>
			<td>-</td>
			<td>Available from RIKEN BRC and Addgene</td>
		</tr>
		<tr>
			<td>pK273. CAG-loxP-STOP-loxP-CyRFP-ires-tTA-WPRE</td>
			<td>Authors</td>
			<td>-</td>
			<td>Available from authors</td>
		</tr>
		<tr>
			<td>Isoflurane</td>
			<td>Wako</td>
			<td>099-06571</td>
			<td></td>
		</tr>
		<tr>
			<td>410 Anaesthesia Unit (isoflurane gas machine)</td>
			<td>Univentor</td>
			<td>8323101</td>
			<td></td>
		</tr>
		<tr>
			<td>Vetbond (tissue adhesive)</td>
			<td>3M</td>
			<td>084-1469SB</td>
			<td></td>
		</tr>
		<tr>
			<td>M&#181;ltiFlex Round (loading tip)</td>
			<td>Sorenson</td>
			<td>13810</td>
			<td></td>
		</tr>
		<tr>
			<td>Gelfoam (gelatin sponge)</td>
			<td>Pfizer</td>
			<td>09-0353-01</td>
			<td></td>
		</tr>
		<tr>
			<td>Agarose</td>
			<td>Sigma</td>
			<td>A9793</td>
			<td>Low melting point</td>
		</tr>
		<tr>
			<td>Round-shaped coverslip</td>
			<td>Matsunami</td>
			<td>-</td>
			<td>Custom made</td>
		</tr>
		<tr>
			<td>Unifast 2 (dental cement)</td>
			<td>GC</td>
			<td>-</td>
			<td></td>
		</tr>
		<tr>
			<td>Titanium bar</td>
			<td>Authors</td>
			<td>-</td>
			<td>Custom made (see Figure 1G)</td>
		</tr>
		<tr>
			<td>Rimadyl (carprofen)</td>
			<td>Zoetis</td>
			<td>-</td>
			<td>Injectable</td>
		</tr>
		<tr>
			<td>2-photon microscope</td>
			<td>Zeiss</td>
			<td>LSM7MP</td>
			<td></td>
		</tr>
		<tr>
			<td>Titanium-sapphire laser</td>
			<td>Spertra-Physics</td>
			<td>Mai-Tai eHPDS</td>
			<td></td>
		</tr>
		<tr>
			<td>Titanium plate</td>
			<td>Authors</td>
			<td>-</td>
			<td>Custom made (see Figure 2A)</td>
		</tr>
		<tr>
			<td>IMARIS, FilamentTracer, MeasurementPro</td>
			<td>BITPLANE</td>
			<td></td>
			<td></td>
		</tr>
		<tr>
			<td>Goniometer stage</td>
			<td>Thorlabs</td>
			<td>GN2/M</td>
			<td></td>
		</tr>
	</tbody>
</table>

in vivo two-photon imaging of cortical neurons in neonatal mice

Two-photon imaging is a powerful tool for the in vivo analysis of neuronal circuits in the mammalian brain. However, a limited number of in vivo imaging methods exist for examining the brain tissue of live newborn mammals. Herein we summarize a protocol for imaging individual cortical neurons in living neonatal mice. This protocol includes the following two methodologies: (1) the Supernova system for sparse and bright labeling of cortical neurons in the developing brain, and (2) a surgical procedure for the fragile neonatal skull. This protocol allows the observation of temporal changes of individual cortical neurites during neonatal stages with a high signal-to-noise ratio. Labeled cell-specific gene silencing and knockout can also be achieved by combining the Supernova with RNA interference and CRISPR/Cas9 gene editing systems. This protocol can, thus, be used for analyzing the developmental dynamics of cortical neurons, molecular mechanisms that control the neuronal dynamics, and changes in neuronal dynamics in disease models.

Figures 2D - 2F show representative results of two-photon time-lapse imaging of layer 4 cortical neurons using the present protocol. For the purpose of analysis, select neurons with clear dendritic morphology throughout the imaging periods. We analyzed the dendritic morphology of imaged neurons using morphological analysis software. Representative dendritic morphology reconstruction is shown in Figure 2F. Neurons showing disc...

Watch this Scientific Journal Video about In Vivo Two-photon Imaging of Cortical Neurons in Neonatal Mice at JoVE.com

In Vivo Two-photon Imaging of Cortical Neurons in Neonatal Mice

We present an in vivo two-photon imaging protocol for imaging the cerebral cortex of neonatal mice. This method is suitable for analyzing the developmental dynamics of cortical neurons, the molecular mechanisms that control the neuronal dynamics, and the changes in neuronal dynamics in disease models.

In Vivo Two-photon Imaging of Cortical Neurons in Neonatal Mice

Two-photon imaging is a powerful tool for the in vivo analysis of neuronal circuits in the mammalian brain. However, a limited number of in vivo imaging ...

This method can help to answer key questions in neuroscience, especially those related to neuron socket formation. The main advantage of this technique is that researchers can analyze the morphological changes of individual neurons in living neonatal mice. Begin with an anesthetized post-natal day five pup and proceed only in the absence of a reaction to the tail pinch test.First, sterilize the scalp by wiping it with 70%ethanol. Then, use scissors sterilized with 70%ethanol to remove approximately 20 square millimeters of the skin covering the skull. Next, use sterile forceps and a clean cotton swab soaked in cortex buffer, to remove the fascia of the skull.Use a loading tip to apply tissue adhesive to the incised skin surface to stop the bleeding while avoiding the area to be imaged. Place the pup on another heating pad, set to 37 degrees Celsius, and allow it to recover from anesthesia. Wait approximately 30 minutes until the tissue adhesive has dried and solidified.Once the tissue adhesive has dried, begin the cranial window preparation on the re-anesthetized mouse. Apply one drop of cortex buffer onto the skull, then use a sterile razor blade to carefully open a one millimeter diameter area of the skull, leaving the dura intact. Apply cortex buffer to keep the brain surface moist.Use a small piece of gelatin sponge soaked in cortex buffer to stop any bleeding. Use a fresh piece to compress one side of the craniotomy and drain any buffer and blood from the dural surface without touching the dura. This is the most critical step to prepare clear window.The dura must be undamaged and the brush should be removed from the exposed dura. Next, use a pipette tip to apply a thin layer of one percent low melting agarose, dissolved in cortex buffer. Apply a round, three millimeter glass cover slip onto the agarose gel layer.Remove all bubbles between the cover slip and the agarose gel layer by pouring in excess of agarose gel between them. Use tweezers to remove the excess gel, protruding from under the cover slip. Mix cement powder and the cement liquid.Use a pipette tip to apply the mixture to the skull before it becomes solidified. Then, attach a custom made titanium bar to the cranial bone using dental cement. Align the titanium bar, and the cover slip in parallel to easily capture images.Cover the exposed skull with dental cement. Then, subcutaneously inject an analgesic. Place the pup in a recovery cage on a 37 degrees celsius heat pad for an hour until the dental cement has solidified.To begin imaging, first set the two-photon laser wavelength. For RFP excitation, use a wavelength of 1000 nanometers. Wipe the surface of the cover slip with 70%ethanol.Attach the anesthetized pup to the titanium plate on the imaging stage, using the titanium bar. Use the goniometer stage, to adjust the head, such that the cover slip is parallel to the objective lens. Maintain the body temperature of the pup during imaging using a heating pad set to 37 degrees Celsius and reduce the isoflurane concentration to 0.7%to 1%Place the imaging stage under the 20x objective lens of the two photon microscope.Apply one drop of water onto the cover slip. Set the software to acquire Z-stack images at 1.4 micron intervals. For layer four neuron imaging, set the Z width to between 150 and 300 microns to image the entire dendritic morphology.Use slow scanning and averaging to get clear images showing the neuronal morphology. It usually takes more than 20 minutes to acquire the entire dendritic morphology. This image shows a representative Z-stack image of the layer four cortical neurons of P5 pup.The arrow indicates the neuron to be analyzed. Neurons with blurred dendrites should be removed from the analysis. This image shows a higher magnification image of the indicated neuron in the prior image.Blue arrowheads indicate dendritic tips that will be retracted at the next time point, and the small white arrowheads indicate the axon of a neighboring cell. After 4.5 hours, the dendritic tips with blue arrowheads are retracted, and the dendritic tips with yellow arrowheads are elongated. A representative dendritic morphology reconstruction is shown here, neurons showing disconnected dendrites as seen here, should be excluded from analyses.While attempting this procedure, it's important to keep the dura intact, during the process. Using this procedure, other methods like in the propulsion imaging can be performed to answer additional questions related to the neuron activity pattern in neonatal brain.

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11.9K Views.  Kumamoto University. This method can help to answer key questions in neuroscience, especially those related to neuron socket formation. The main advantage of this technique is that researchers can analyze the morphological changes of individual neurons in living neonatal mice. Begin with an anesthetized post-natal day five pup and proceed only in the absence of a reaction to the tail pinch test.First, sterilize the scalp by wiping it with 70%ethanol. Then, use scissors sterilized with 70%ethanol to remove ...