A Large Lateral Craniotomy Procedure for Mesoscale Wide-field Optical Imaging of Brain Activity

Summary

This protocol presents a method for creating a large unilateral craniotomy over the temporal and parietal regions of the mouse cerebral cortex. This is especially useful for real time imaging over an expansive area of a cortical hemisphere.

Abstract

The craniotomy is a commonly performed procedure to expose the brain for in vivo experiments. In mouse research, most labs utilize a small craniotomy, typically 3 mm x 3 mm. This protocol introduces a method for creating a substantially larger 7 mm x 6 mm cranial window exposing most of a cerebral hemisphere over the mouse temporal and parietal cortices (e.g., bregma 2.5 - 4.5 mm, lateral 0 - 6 mm). To perform this surgery, the head must be tilted approximately 30° and much of the temporal muscle must be retracted. Due to the large amount of bone removal, this procedure is intended only for acute experiments with the animal anesthetized throughout the surgery and experiment.

The main advantage of this innovative large lateral cranial window is to provide simultaneous access to both medial and lateral areas of the cortex. This large unilateral cranial window can be used to study the neural dynamics between cells, as well as between different cortical areas by combining multi-electrode electrophysiological recordings, imaging of neuronal activity (e.g., intrinsic or extrinsic imaging), and optogenetic stimulation. Additionally, this large craniotomy also exposes a large area of cortical blood vessels, allowing for direct manipulation of the lateral cortical vasculature.

Introduction

The craniotomy is a standard procedure used by neuroscientists to reveal a portion of the brain. Since the dawn of electrophysiology, the craniotomy has allowed unprecedented breakthroughs in the field of neuroscience. Dense mapping of the cerebral cortex with electrodes has led to experiments testing hypotheses and theories based on these maps. We have recently entered a new era where the craniotomy is being utilized for in vivo imaging of cortical blood flow^1,2,3 and neurovascular architecture⁴, enabling real time visualization of cortical a....

Protocol

The following protocol follows the University of Lethbridge Animal Care Committee (ACC) guidelines, and is conducted in accordance with the standards of the Canadian Council on Animal Care (CCAC).

1. Preparation

1. For prolonged study periods, autoclave all opened surgical supplies and ensure that sterility is maintained throughout the surgery. If multiple surgeries are required, autoclave between surgeries. 
2. Ensure there is plenty of brain buffer on hand (at least 50 mL). The solution is comprised of 134 mM sodium chloride, 5.4 mM potassium, 1 mM magnesium chloride hexahydrate, 1.8 mM calcium chloride dihydrate, and....

Results

To study the interactions between cortical areas within a single hemisphere, we used a large craniotomy extending across the sagittal sinus and 5 - 6 mm lateral. This cranial window included primary (motor, somatosensory, visual, auditory), secondary (motor, visual), and association (retrosplenial, cingulate, parietal association) cortices of right brain hemispheres (Figure 3A). For this work we used voltage sensitive dye (VSD) imaging, which reflects changes.......

Discussion

This innovative protocol for a large cranial window enables simultaneous imaging over the temporal and parietal areas of the cerebral cortex. Combined with optical imaging, it can help to reveal neural dynamics within cortical areas during spontaneous and stimulus-induced activity. This expansive craniotomy also exposes a large extension of the cortical vasculature network, including the proximal end of the middle cerebral artery (MCA), enabling in vivo imaging of blood flow and direct manipulation of lateral ve.......

Materials

List of materials used in this article

Name	Company	Catalog Number	Comments
Heating Pad	FHC	40-90-2
Fine Scissors	Fine Science Tools	14058-09
Forceps	Fine Science Tools	11251-35	2 or more pairs are recommended
Spring scissors	Fine Science Tools	15000-00, 15000-10	1 pair should be designated for dura removal
Jet tooth shade powder	LANG Dental	Jet Tooth Shade Powder	to be mixed with the Jet Liquid
Jet tooth shade liquid	LANG Dental	Jet Tooth Shade Liquid	to be mixed wihth the Jet Powder
Drill Heads - Carbide Burs FG 1/4 389	Midwest Dental	385201
Agarose Powder	Sigma-Aldrich	A9793
Gelfoam	Sinclair Dental Canada	Pfizer Gelfoam
Isoflurane	Western Drug Distribution Centre Ltd	124125
Lidocaine 2% Epinephrine	Western Drug Distribution Centre Ltd	125299
Dexamethazone 5 mg/mL	Western Drug Distribution Centre Ltd	125231
Butyl cyanoacrylate glue (VetBond)	Western Drug Distribution Centre Ltd	12612