Hybrid Microdrive System with Recoverable Opto-Silicon Probe and Tetrode for Dual-Site High Density Recording in Freely Moving Mice

Summary

This protocol describes the construction of a hybrid microdrive array that allows implantation of nine independently adjustable tetrodes and one adjustable opto-silicon probe in two brain regions in freely moving mice. Also demonstrated is a method for safely recovering and reusing the opto-silicon probe for multiple purposes.

Abstract

Multi-regional neural recordings can provide crucial information to understanding fine-timescale interactions between multiple brain regions. However, conventional microdrive designs often only allow use of one type of electrode to record from single or multiple regions, limiting the yield of single-unit or depth profile recordings. It also often limits the ability to combine electrode recordings with optogenetic tools to target pathway and/or cell type specific activity. Presented here is a hybrid microdrive array for freely moving mice to optimize yield and a description of its fabrication and reuse of the microdrive array. The current design employs nine tetrodes and one opto-silicon probe implanted in two different brain areas simultaneously in freely moving mice. The tetrodes and the opto-silicon probe are independently adjustable along the dorsoventral axis in the brain to maximize the yield of unit and oscillatory activities. This microdrive array also incorporates a set-up for light, mediating optogenetic manipulation to investigate the regional- or cell type-specific responses and functions of long-range neural circuits. In addition, the opto-silicon probe can be safely recovered and reused after each experiment. Because the microdrive array consists of 3D-printed parts, the design of microdrives can be easily modified to accommodate various settings. First described is the design of the microdrive array and how to attach the optical fiber to a silicon probe for optogenetics experiments, followed by fabrication of the tetrode bundle and implantation of the array into a mouse brain. The recording of local field potentials and unit spiking combined with optogenetic stimulation also demonstrate feasibility of the microdrive array system in freely moving mice.

Introduction

It is crucial to understand how neuronal activity supports cognitive process, such as learning and memory, by investigating how different brain regions dynamically interact with each other. To elucidate dynamics of the neural activity underlying cognitive tasks, large-scale extracellular electrophysiology has been conducted in freely moving animals with the aid of microdrive arrays^1,2,3,4. In the past two decades, several types of microdrive array have been developed to implant electrodes into multiple brain regions for rats

Protocol

All methods described here have been approved by the Institutional Animal Care and Use Committee (IACUC) of the University of Texas Southwestern Medical Center.

1. Preparations of microdrive array parts

1. Print the microdrive array parts using a 3D printer using dental model resin (Figure 1A,B). Ensure that the thickness of individual 3D printed layers is less than 50 µm to keep the small holes on the printed parts clear and viable.
   NOTE: The microdrive array consists of five parts (Figure 1C): (1) the main body of the microdrive array, which includes nine microdrive-screw....

Results

The microdrive array was constructed within 5 days. The timeline of microdrive preparation is described in Table 2. Using this microdrive, nine tetrodes and one silicon probe were implanted into the hippocampal CA1 and MEC of the mouse [21 week old/29 g body weight male pOxr1-Cre (C57BL/6 background)], respectively. This transgenic mouse expresses Cre in MEC layer III pyramidal neurons. The mouse was injected with 200 nL of AAV5-DIO-ChR2-YFP (titer: 7.7 x 10¹² gc/mL) into the MEC 10 weeks befo.......

Discussion

The protocol demonstrates how to construct and implant a hybrid microdrive array that allows recording of neural activities from two brain areas using independent adjustable tetrodes and a silicon-probe in freely behaving mice. It also demonstrates optogenetic experiments and the recovery of the silicon probe after experiments. While adjustable silicon probe³³ or opto-silicon probe³⁶ implantation are previously demonstrated in mice, this protocol has clear advantages in the.......

Materials

Name	Company	Catalog Number	Comments
#00-90 screw	J.I. Morris	#00-90-1/8	EIB screws
#0-80 nut	Small Parts	B00DGB7CT2	brass nut for holding fiber ferrule holder
#0-80 screw	Small Parts	B000FMZ57G	brass machine screw for probe connector mount, fiber ferrule holder, and shielding cone
22 Ga polyetheretherketone tubes	Small Parts	SLPT-22-24	for attaching to the shuttle, 0.025 inches inner diameter
23 Ga stainless tubing	Small Parts	HTX-23R	for tetrode
23 Ga stainless wire	Small Parts	HTX-23R-24-10	for L-shape/support wire
26 Ga stainless wire	Small Parts	GWX-0200	for guide-posts
30 Ga stainless wire	Small Parts	HTX-30R	for tetrode
3-D CAD software package	Dassault Systèmes	SolidWorks 2003
3D printer	FormLab	Form2
5.5mil polyimide insulating tubes	HPC Medical	72113900001-012
aluminum foil tape	Tyco	Tyco Adhesives 617022 Aluminum Foil Tape	for the alternative shielding cone
conductive paste	YSHIELD	HSF54	for shielding cone
customized screws for silicon-probe microdrive	AMT	UNM1.25-HalfMoon	half-moon stainless screw, 1.5 mm diameter, 300 µm thread pitch
customized screws for tetrode microdrive	AMT	Yamamoto_0000-160_9mm	slotted stainless screw, 0.5 mm diameter, 160 µm thread pitch, custom-made to order for our design
dental acrylic	Stoelting	51459
dental model resin	FormLab	RS-F2-DMBE-02
Dremel rotary tool	Dremel	model 800	a grinder
drill bit	Fine Science Tool	19007-05
electric interface board	Neuralynx	EIB-36-Narrow
epoxy	Devcon	GLU-735.90	5 minutes epoxy
eye ointment	Dechra	Puralube Ophthalmic Ointment	to prevent mice eyes from drying during surgery
fiber polishing sheet	Thorlabs	LFG5P	for polishing the optical fiber
fine tweezers	Protech International	15-368	for loading/recovering the silicon probe
gold pins	Neuralynx	EIB Pins Small
ground wire	A-M Systems	781500	0.010 inch bare silver wire
headstage preamp	Neuralynx	HS-36
impedance meter	BAK electronics	Model IMP-2	1 kHz testing frequency
mineral oil	ZONA	36-105	for lubricating screws and wires
optical fiber	Doric	MFC_200/260-0.22_50mm_ZF1.25(G)_FLT
Recording system	Neuralynx	Digital Lynx 4SX
ruby fiber scribe	Thorlabs	S90R	for cleaving the optical fiber
silicon grease	Fine Science Tool	29051-45
silicon probe	Neuronexus	A1x32-Edge-5mm-20-177	Fig. 3, 4A, 4B, 5
silicon probe	Neuronexus	A1x32-6mm-50-177	Fig. 4C
silicon probe washing solution	Alcon	AL10078844	contact lens cleaner
silicone lubber	Smooth-On	Dragon Skin 10 FAST	for preparation of microdrive mold
silver paint	GC electronic	22-023	silver print II coating, used for ground wires
skull screw	Otto Frei	2647-10AC	0.8 mm diameter, 0.200 mm thread pitch
standard surgical scissors	ROBOZ	RS-5880
stereotaxic apparatus	Kopf	Model 942
super glue	Loctite	LOC230992	for applying to guide-posts
surgical tweezers	ROBOZ	RS-5135
Tetrode Twister	Jun Yamamoto	TT-01
tetrode wires	Sandvik	PX000004