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

Summary

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.

Abstract

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.

Introduction

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 brain^1,2. However, ....

Protocol

Experiments should be performed in accordance with the animal welfare guidelines prescribed by the experimenter'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 vectors^5,6. The Supernova system consists of the following two vectors: TRE-Cre and CAG-loxP-STOP-loxP-Gene X-ires-tTA-WPRE. .......

Discussion

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, .......

Materials

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