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Background Novel imaging technology and procedures were developed to study brain function in preadolescent awake marmosets never exposed to anesthesia. Methods A radiofrequency transmit and receive, head only volume coil was designed and integrated into a holding system. An acclimation procedure was developed without the use of anesthesia or sedation that allowed for awake imaging. Preadolescent 8-month old male and female marmosets were imaged for resting state BOLD functional connectivity to assess the status of the default mode network. Levels of reactivity during acclimation sessions and behavioral stress following imaging were assessed. Results Data on functional coupling in the default mode network suggest the organization of connectivity to the prefrontal cortex is not fully developed at 8 months of age. The stress associated with the imaging procedure is comparable to that observed when marmosets are removed from their home cage and temporarily isolated from the family. Comparison to other methods The design of the radiofrequency coil provides B1 homogeneity across the entire brain without signal drop off. The unique design of the head cradle obviates the need for any stabilizing surgery, ear bars or bite bar and could be adapted to any size marmoset. The acclimation requires no anesthesia or sedation at any time in the early life of the developing marmoset, a condition that better reflects the human experience. Conclusion A method is provided for imaging functional activity in the brain of fully awake preadolescent marmosets without any history of anesthesia or sedation.

Functional magnetic resonance imaging (fMRI) in conscious animals is evolving as a critical tool for neuroscientists. The present study explored the effectiveness of an acclimation procedure in minimizing the stress experienced by the animal as assessed by alterations in physiological parameters including heart rate, respiratory rate, and serum corticosterone levels. Results confirm that as the stress of the protocol is minimized, there is a significant decrease in head movements and enhancement in data quality. The feasibility of improving the quality of fMRI data acquired in alert rats by utilizing a relatively simple technique is presented.

Functional 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.

Functional magnetic resonance imaging (fMRI) was used to assess the effects of cocaine on brain activation in fully conscious rats. Methods were developed to image cocaine-induced changes in blood-oxygen-level-dependent (BOLD) signal without the peripheral cardiac and respiratory complications associated with psychostimulant administration. Using spin echo planar imaging (EPI), conscious rats were imaged in a 4.7 T spectrometer prior to and following the intracerebroventricular injection of cocaine (20 microg) in artificial cerebrospinal fluid (10 uL). Within 5 min of injection, there was a significant increase in BOLD signal intensity in the substantia nigra, ventral tegmental area, nucleus accumbens, dorsal striatum and prefrontal cortex, as compared to vehicle controls. Minimal negative BOLD signal changes were observed in response to cocaine and no significant perturbations in normal cardiovascular and respiratory function. These findings demonstrate the technical feasibility of studying psychostimulant-induced brain activity using functional MRI in conscious rats.

A 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.