Published: August 28th, 2021
This protocol describes a method for obtaining stable resting-state functional magnetic resonance imaging (rs-fMRI) data from a rat using low dose isoflurane in combination with low dose dexmedetomidine.
Resting-state functional magnetic resonance imaging (rs-fMRI) has become an increasingly popular method to study brain function in a resting, non-task state. This protocol describes a preclinical survival method for obtaining rs-fMRI data. Combining low dose isoflurane with continuous infusion of the α2 adrenergic receptor agonist dexmedetomidine provides a robust option for stable, high-quality data acquisition while preserving brain network function. Furthermore, this procedure allows for spontaneous breathing and near-normal physiology in the rat. Additional imaging sequences can be combined with resting-state acquisition creating experimental protocols with anesthetic stability of up to 5 h using this method. This protocol describes the setup of equipment, monitoring of rat physiology during four distinct phases of anesthesia, acquisition of resting-state scans, quality assessment of data, recovery of the animal, and a brief discussion of post-processing data analysis. This protocol can be used across a wide variety of preclinical rodent models to help reveal the resulting brain network changes that occur at rest.
Resting-state functional magnetic resonance imaging (rs-fMRI) is a measure of the blood-oxygen-level-dependent (BOLD) signal when the brain is at rest and not engaged in any particular task. These signals can be used to measure correlations between brain regions to determine the functional connectivity within neural networks. rs-fMRI is widely used in clinical studies due to its non-invasiveness and the low amount of effort required of patients (as compared to task-based fMRI) making it optimal for diverse patient populations1.
Technological advances have allowed rs-fMRI to be adapted for use in rodent models to unco....
All experiments were performed on a 9.4 T MRI scanner, and were approved by the Institutional Animal Care and Use Committee at Dartmouth College. Additional approval was obtained to record and show the animals used in the video and figures below.
1. Preparations before scanning
Following each resting-state scan, stability is assessed using an independent component analysis (ICA; example script included in Supplementary Files). Figure 6 shows examples of component outputs from resting-state scans. Figure 6a shows a signal component from a scan with high stability. Note that spatially, the component has high regionality. Within the time course below the spatial component, the signal is stable and not predictable, indicat.......
Stability of the animal, both physically and physiologically, is key to obtaining high-quality resting-state data. This protocol achieves stability by moving through four distinct phases of anesthesia. It is imperative that the animal has met the set physiological thresholds before moving to the next phase of anesthesia; since this method relies on physiological autoregulatory mechanisms, individual animals may require slightly different amounts of time at each anesthesia phase. It is our experience that taking more time.......
This work was supported by funding from the National Institute of Health (NIH)'s National Institute on Drug Abuse (NIDA) [DJW, EDKS, and EMB were supported by Grant R21DA044501 awarded to Alan I. Green and DJW was supported by Grant T32DA037202 to Alan J. Budney] and the National Institute on Alcohol Abuse and Alcoholism (NIAAA) [Grant F31AA028413 to Emily D. K. Sullivan]. Additional support was provided through Alan I. Green's endowed fund as the Raymond Sobel Professor of Psychiatry at Dartmouth.
Hanbing Lu is supported by the National Institute on Drug Abuse Intramural Research Program, NIH.
|Varian upgraded with Bruker console running Paravision 6.0.1 software
|Analysis of Functional NeuroImages (AFNI)
|Freely available at: https://afni.nimh.nih.gov/
|rat holder with bite bar, nose cone and ear bars
|Animal Physiology Monitoring & Gating System
|MR-compatible system including oxygen saturation, temperature, respiration and fiber optic pulse oximetry add-on
|Antisedan (atipamezole hydrochloride)
|Zoetis, Manufacturer Item #10000449
|Ceramic MRI-Safe Scissors
|Wahl touch-up trimmer combo kit, Manufacturer Item #09990-1201
|Dexmedesed (dexmedetomidine hydrochloride)
|Dechra Veterinary Products, Manufacturer Item#17033-005-10
|Digital Rectal Thermometer Covers
|FMRIB Software Library
|MELODIC Version 3.15
|Freely available at: https://fsl.fmrib.ox.ac.uk/fsl/fslwiki
|Hemostat forceps, straight
|Patterson Private Label, Manufacturer Item #14043-0704-06
|Lab Tape, 3/4"
|Needles, 23 gauge
|plastic hub removed
|Parafilm Laboratory Film
|Medline Industries Inc., Manufacturer Item #HSFHS234526A
|Planar Surface Coil
|0.023" (inner diameter), 0.038" (outer diameter)
|Puralube Ophthalmic Ointment
|Dechra Veterinary Products, Manufacturer Item #211-38
|Sprague Dawley Rats
|400 SAS SD
|Sterile 0.9% Saline Solution
|Aspen Vet, Manufacturer Item #14208186
|Sterile Alcohol Prep Pads
|Surgical Tape, 1" (3M Durapore)
|3M Healthcare, "wide medical tape"
|Surgical White Paper Tape, 1/2" (3M Micropore)
|Syringes, 1 mL w/ 25 gauge needle
|Syringes, 3 mL
|Vented induction and scavenging system
|2 liter induction chamber with active scavenging
|scavenging cube, "vacuum"
|nose cone, non-rebreathing
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