Browsing by keyword "Restraint, Physical"
Now showing items 1-4 of 4
-
A dual RF resonator system for high-field functional magnetic resonance imaging of small animalsA new apparatus has been developed that integrates an animal restrainer arrangement for small animals with an actively tunable/detunable dual radio-frequency (RF) coil system for in vivo anatomical and functional magnetic resonance imaging of small animals at 4.7 T. The radio-frequency coil features an eight-element microstrip line configuration that, in conjunction with a segmented outer copper shield, forms a transversal electromagnetic (TEM) resonator structure. Matching and active tuning/detuning is achieved through fixed/variable capacitors and a PIN diode for each resonator element. These components along with radio-frequency chokes (RFCs) and blocking capacitors are placed on two printed circuit boards (PCBs) whose copper coated ground planes form the front and back of the volume coil and are therefore an integral part of the resonator structure. The magnetic resonance signal response is received with a dome-shaped single-loop surface coil that can be height-adjustable with respect to the animal's head. The conscious animal is immobilized through a mechanical arrangement that consists of a Plexiglas body tube and a head restrainer. This restrainer has a cylindrical holder with a mouthpiece and position screws to receive and restrain the head of the animal. The apparatus is intended to perform anatomical and functional magnetic resonance imaging in conscious animals such as mice, rats, hamsters, and marmosets. Cranial images acquired from fully conscious rats in a 4.7 T Bruker 40 cm bore animal scanner underscore the feasibility of this approach and bode well to extend this system to the imaging of other animals.
-
Imaging brain activation in nicotine-sensitized ratsOur purpose was to determine if sensitization to nicotine could be assessed using functional magnetic resonance imaging (fMRI) with BOLD contrast. Sensitization describes a phenomenon whereby subsequent doses of a drug produce greater responses than the initial dose. Robust locomotor sensitization was demonstrated in adult male Sprague-Dawley rats by the daily administration of nicotine 0.4 mg/kg over 5 days. In parallel experiments, brain activity was monitored using fMRI in animals receiving their first dose (acute) or fifth dose of nicotine (sensitized) and appropriate saline controls. Compared to the acute nicotine animals, brain activity in the sensitized animals demonstrated prolonged BOLD activation in response to nicotine in the hippocampus, nucleus accumbens, prefrontal cortex, ventral pallidum and ventral tegmentum, and more intense peak activation in the hippocampus, prefrontal cortex and ventral tegmentum. In addition, sensitization was associated with a relative decrease in activation in the anterior cingulate gyrus. Furthermore, despite the rich endowment of nicotinic receptors in the visual cortex there was no change in activation with sensitization, thus establishing the specificity of the observed pattern of regional activation and inhibition. Taken together, the current studies support the premise that nicotine sensitization is accompanied by changes in brain activation including a sensitized BOLD response in the extended limbic system that may subserve the process of dependence.
-
Imaging brain activity in conscious animals using functional MRIFunctional magnetic resonance imaging (fMRI) in humans has helped improve our understanding of the neuroanatomical organization of behavior. Unfortunately, fMRI in animal studies has not kept pace with the human work. Experiments are limited because animals must be anesthetized to prevent motion artifacts, precluding most studies involving neuroimaging of brain activity during behavior. The present study tested a newly developed head and body holder for performing fMRI in fully conscious animals. Significant changes in signal intensities were observed in the somatosensory cortex of conscious rats in response to electrical shock of the hindpaw. These changes in evoked signal ranged between 4 and 19% and were accompanied by significant increases in local cerebral blood flow. The fMRI study was performed with a 2.0-Tesla spectrometer. Using this non-invasive method of imaging brain activity in conscious animals, it is now possible to perform developmental studies in animal models of neurological and psychiatric disorders.