Deep Brain Stimulation with Simultaneous fMRI in Rodents

Summary

This protocol describes a standard method for simultaneous functional magnetic resonance imaging and deep brain stimulation in the rodent. The combined use of these experimental tools allows for the exploration of global downstream activity in response to electrical stimulation at virtually any brain target.

Abstract

In order to visualize the global and downstream neuronal responses to deep brain stimulation (DBS) at various targets, we have developed a protocol for using blood oxygen level dependent (BOLD) functional magnetic resonance imaging (fMRI) to image rodents with simultaneous DBS. DBS fMRI presents a number of technical challenges, including accuracy of electrode implantation, MR artifacts created by the electrode, choice of anesthesia and paralytic to minimize any neuronal effects while simultaneously eliminating animal motion, and maintenance of physiological parameters, deviation from which can confound the BOLD signal. Our laboratory has developed a set of procedures that are capable of overcoming most of these possible issues. For electrical stimulation, a homemade tungsten bipolar microelectrode is used, inserted stereotactically at the stimulation site in the anesthetized subject. In preparation for imaging, rodents are fixed on a plastic headpiece and transferred to the magnet bore. For sedation and paralysis during scanning, a cocktail of dexmedetomidine and pancuronium is continuously infused, along with a minimal dose of isoflurane; this preparation minimizes the BOLD ceiling effect of volatile anesthetics. In this example experiment, stimulation of the subthalamic nucleus (STN) produces BOLD responses which are observed primarily in ipsilateral cortical regions, centered in motor cortex. Simultaneous DBS and fMRI allows the unambiguous modulation of neural circuits dependent on stimulation location and stimulation parameters, and permits observation of neuronal modulations free of regional bias. This technique may be used to explore the downstream effects of modulating neural circuitry at nearly any brain region, with implications for both experimental and clinical DBS.

Introduction

Determining the global downstream effects of neural circuit activity represents a major challenge and goal for many areas of systems neuroscience. A paucity of tools are currently available that meet this need, and thus there is a demand for increased accessibility of the appropriate experimental setups. One such method for evaluating the global consequence of neural circuit activation relies on the simultaneous application of deep brain electrical stimulation (DBS) and functional MRI (fMRI). DBS-fMRI allows for the detection of downstream responses to circuit activation on a large spatial scale, and can be applied at virtually any stimulation target. This toolse....

Protocol

Ethics Statement: This procedure is in accordance with the National Institutes of Health Guidelines for Animal Research (Guide for the Care and Use of Laboratory Animals) and is approved by the University of North Carolina Institutional Animal Care and Use Committee.

1. Electrode Implantation

The first step is electrode implantation. In this step, an electrode is unilaterally implanted into the subthalamic nucleus (STN), a small nucleus with translational significance for Parkinson’s disease treatment using the following methods:

1. Sterilize all surgical equipment using an autoclave, or antiseptic....

Results

Representative functional data were acquired according to the above protocol in a single rat with a stimulating electrode implanted to the subthalamic nucleus on the right side. An illustration of essential setup for DBS fMRI image acquisition is provided in Figure 1. Stimulation was applied consistent with the above protocol, with an amplitude of 0.3 mA, frequency of 130 Hz and pulse width of 0.09 msec. Robust activation of ipsilateral motor cortex has been consistently visualized using this protocol wi.......

Discussion

Simultaneous DBS and fMRI represents a promising experimental toolkit for the identification and characterization of global downstream responses to neural circuit stimulation, in vivo. The major advantage of this technique over other available tools, such as electrophysiological recordings, lies in the relatively unbiased nature of fMRI, whereby a large and diverse area of brain tissue can be examined for responsiveness to DBS at any target. Although the described protocol is specific for DBS-fMRI in the ra.......

Materials

List of materials used in this article

Name	Company	Catalog Number	Comments
Isoflurane (Forane)	Baxter	1001936060
Dexmedetomidine (Dexdomitor)	Pfizer	145108-58-3
Pancuronium Bromide	Selleckchem	S2497
9.4 T Small Animal MRI	Bruker		BioSpec System with BGA-9S gradient
Sterotactic Frame	Kopf		Model 962
Small Animal Ventilator	CWE, Inc.	12-02100	Model SAR-830
Dental Cement	A-M Systems	525000	Teets Cold Curing
MouseOx Plus System	STARR Life Science Corp.
Capnometer	Surgivet, Smith Medical		V9004 Series
Stimulus Isolator	World Precision Instruments		Model A365
MR-compatible Brass Screws	McMaster Carr	94070A031	0-80 thread size, 1/4 in. Can be cut to desired length.
Tungsten Wire	California Fine Wire Company	100211	Used to construct MR-compatible stimulating microelectrode
Syringe Pump	Harvard Appartus		Model PHD 2000 (not MRI-compatible)