Construction of Local Field Potential Microelectrodes for in vivo Recordings from Multiple Brain Structures Simultaneously

Summary

The present protocol describes the construction of custom-made microelectrode arrays to record local field potentials in vivo from multiple brain structures simultaneously.

Abstract

Researchers often need to record local field potentials (LFPs) simultaneously from several brain structures. Recording from multiple desired brain regions requires different microelectrode designs, but commercially available microelectrode arrays often do not offer such flexibility. Here, the present protocol outlines the straightforward design of custom-made microelectrode arrays to record LFPs from multiple brain structures simultaneously at different depths. This work describes the construction of the bilateral cortical, striatal, ventrolateral thalamic, and nigral microelectrodes as an example. The outlined design principle offers flexibility, and the microelectrodes can be modified and customized to record LFPs from any structure by calculating stereotaxic coordinates and quickly changing the construction accordingly to target different brain regions in either freely moving or anesthetized mice. The microelectrode assembly requires standard tools and supplies. These custom microelectrode arrays allow investigators to easily design microelectrode arrays in any configuration to track neuronal activity, providing LFP recordings with millisecond resolution.

Introduction

Local field potentials (LFPs) are the electric potentials recorded from the extracellular space in the brain. They are generated by ion concentration imbalances outside of neurons and represent the activity of a small, localized population of neurons, allowing to precisely monitor the activity of a specific brain region compared to the macroscale EEG recordings¹. As an estimate, the LFP microelectrodes separated by 1 mm correspond to two completely different populations of neurons. While EEG signal is filtered by brain tissue, cerebrospinal fluid, skull, muscle, and skin, LFP signal is a reliable marker of local neuronal activity

Protocol

The present work is approved by the University of Virginia Animal Care and Use Committee. C57Bl/6 mice of both sexes (7-12 weeks) were used for the experiments. The animals were maintained on a 12 h light/12 h dark cycle and had ad libitum access to food and water.

1. Microelectrode construction

1. To construct the microelectrodes, use 50 µm (diameter) diamel-coated nickel-chromium wire (see Table of Materials). Tape one end of the wire at the back of the platform and wrap the wire three times around the nearest knob on the platform (Figure 1A,C

Results

In this work, the LFP microelectrodes were used to map the seizure spread through the basal ganglia¹¹. Simultaneous LFP recordings were performed from the right premotor cortex (where the seizure focus was) and the left VL, striatum, and SNR (Figure 4). Seizure start was identified as deflection of the voltage trace at least twice the baseline (Figure 4A, red arrow). The power spectrum plot¹¹ shows frequency distri.......

Discussion

Historically, microelectrode arrays have been extensively used to record neuronal activity from a specific brain region of interest^{2,3,4,5,6,7,8,9,13}. However, our easy microelectrode design allows recording from multiple .......

Materials

List of materials used in this article

Name	Company	Catalog Number	Comments
Amplifier 16-Channel	A-M Systems	Model 3600	Amplifier
Cranioplasty cement	Coltene	Perm Reeline/Repair Resin Type II Class I Shade - Clear	Cement to hold microelectrodes
Cryostat Microtome	Precisionary	CF-6100	To slice brain
Diamel-coatednickel-chromium wire	Johnson Matthey Inc.	50 µm	Microelectrode wire
Dremel	Dremel	300 Series	To drill holes in mouse skull
Epoxy	CEC Corp	C-POXY 5	Fast setting adhesive
Hemostat	Any		To hold the headset
Forceps	Any		To hold microelectrodes
Light microscope	Nikon	SMZ-10	To see alignment
Ohmmeter	Any		To measurre resistance
Pins (Headers and matching Sockets)	Mill-Max	Interconnects, 833 series, 2 mm grid gull wing surface mount headers and sockets	To attach microelectrodes to
Polymicro Tubing Kit	Neuralynx	ID 100 ± 04 µm, OD 164 ± 06 µm, coating thickness 12 µm	Glass tubes
Pulse Stimulator	A-M Systems	Model 2100	To mark the microelectrode location at the end of the recordings
Scissors	Any		To cut microelectrodes
Superglue	Gorilla		Adhesive
Thick wire 0.008 in. – 0.011 in.	A-M Systems	791900	Tick wire to hold the microelectrode array
Thin wire 0.005 in. - 0.008 in.	A-M Systems	791400	Thin wire for reference and ground