Recording Spatially Restricted Oscillations in the Hippocampus of Behaving Mice

Summary

This protocol describes the recording of local field potentials with multi-shank linear silicon probes. Conversion of the signals using current source density analysis allows the reconstruction of local electrical activity in the mouse hippocampus. With this technique, spatially restricted brain oscillations can be studied in freely moving mice.

Abstract

The local field potential (LFP) emerges from ion movements across neural membranes. Since the voltage recorded by LFP electrodes reflects the summed electrical field of a large volume of brain tissue, extracting information about local activity is challenging. Studying neuronal microcircuits, however, requires a reliable distinction between truly local events and volume-conducted signals originating in distant brain areas. Current source density (CSD) analysis offers a solution for this problem by providing information about current sinks and sources in the vicinity of the electrodes. In brain areas with laminar cytoarchitecture such as the hippocampus, one-dimensional CSD can be obtained by estimating the second spatial derivative of the LFP. Here, we describe a method to record multilaminar LFPs using linear silicon probes implanted into the dorsal hippocampus. CSD traces are computed along individual shanks of the probe. This protocol thus describes a procedure to resolve spatially restricted neuronal network oscillations in the hippocampus of freely moving mice.

Introduction

Oscillations in the LFP are critically involved in information processing by neuronal circuits. They cover a wide spectrum of frequencies, ranging from slow waves (~1 Hz) to fast ripple oscillations (~200 Hz)¹. Distinct frequency bands are associated with cognitive functions including memory, emotional processing, and navigation^2,3,4,5,6,7. Current flow across neuronal membranes constitutes the largest part of the LFP signal⁸....

Protocol

All methods involving living animals have been approved by the Regierungspräsidium Freiburg in accordance with the German Animal Welfare Act.

1. Preparations

1. Design and build an appropriate insertion tool transiently carrying the silicon probe and the electrode connector during the process of implantation. See Figure 1 for an example custom built insertion tool.
2. Carefully release the silicon probe and electrode connector from its packaging using ceramic-tipped forceps.
3. Lift the connector board and securely fix it with a crocodile clamp attached to a stand.
4. Using a stere....

Results

Figure 1 illustrates the insertion tool used for the implantation of silicon probes. Recordings from chronically implanted silicon probes targeting the CA1 area and the granule cell layer of the dentate gyrus are shown in Figure 2. We recorded LFPs from the probe shanks during free movement in the homecage. To minimize the effect of volume conduction, the obtained signals were converted to CSD along each shank of the probe (

Discussion

Increasing evidences indicate that brain oscillations in hippocampal neuronal circuits occur in discrete spatial domains^10,11,16. CSD analysis drastically reduces the influence of volume conduction, a crucial prerequisite for the study of local oscillation events. With this video, we provide a guide to implanting silicon probes into the mouse hippocampus for the analysis of CSD data. We show representative examples of CSD signal.......

Materials

List of materials used in this article

Name	Company	Catalog Number	Comments
Crocodile clamp with stand	Reichelt Elektronik	HALTER ZD-10D
Silicon probe	Cambridge Neurotech	P-series 32
Stereoscope	Olympus	SZ51
Varnish-insulated copper wire	Bürklin Elektronik	89 F 232
Ground screws	Screws & More GmbH (screwsandmore.de)	DIN 84 A2 M1x2
Flux	Stannol	114018
Ceramic-tipped forceps	Fine Science Tools	11210-60
Paraffine Wax	Sigma-Aldrich	327204
Cauterizer	Fine Science Tools	18010-00
Soldering iron	Kurtz Ersa	OIC1300
Multimeter	Uni-T	UT61C
Ethanol	Carl Roth	9065.1
Pasteur pipettes	Carl Roth	EA65.1
Heat sterilizer	Fine Science Tools	18000-45
Stereotaxic frame	David Kopf	Model 1900
Stereotaxic electrode holder	David Kopf	Model 1900
Isoflurane	Abbvie	B506
Oxygen concentrator	Respironix	1020007
Buprenorphine	Indivior UK Limited
Electrical shaver	Tondeo	Eco-XS
Heating pad	Thermolux	463265/-67
Surgical clamps	Fine Science Tools	18050-28
Hydrogen peroxide	Sigma-Aldrich	H1009
Sterile cotton wipes	Carl Roth	EH12.1
Drill	Proxxon	Micromot 230/E
21G injection needle	B. Braun	4657527
Phosphate buffer/phosphate buffered saline
Stereotaxic atlas	Elsevier	9.78012E+12
Surgical scissors	Fine Science Tools	14094-11
Surgical forceps	Fine Science Tools	11272-40
27G injection needles	B. Braun	4657705
Vaseline
Dental cement	Sun Medical	SuperBond T&M
Carprofen	Zoetis	Rimadyl 50mg/ml
Recording amplifier	Intan Technologies	C3323
USB acquisition board	Intan Technologies	C3004
Recording cables	Intan Technologies	C3216
Electrical commutator	Doric lenses	HRJ-OE_FC_12_HARW
Acquisition software	OpenEphys (www.open-ephys.org)	GUI	allows platform-independent data acquisition
Computer for data acquisition
Analysis environment	Python (www.python.org)		allows platform-independent data analysis
Urethane	Sigma-Aldrich
Vibratome	Leica	VT1000
Microscope slides	Carl Roth	H868.1
Cover slips	Carl Roth	H878.2
Embedding medium	Sigma-Aldrich	81381-50G
Distilled water	Millipore	Milli Q	Table-top machine for the production of distilled water
Tergazyme	Alconox	Tergazyme