Physiological effects of a habituation procedure for functional MRI in awake mice using a cryogenic radiofrequency probe.

BACKGROUND: Functional magnetic resonance imaging (fMRI) in mice is typically performed under anesthesia due to difficulties in holding the head of awake mice stably with a conventional three-point fixation method that uses a tooth-bar and earplugs. Although some studies have succeeded in fMRI in awake mice by attaching a head-post on the skull, this cannot be applied to fMRI using a high signal-to-noise ratio (SNR) cryogenic MRI-detector, CryoProbe, because it covers the head of a mouse closely. NEW METHOD: We developed head-fixation implements for awake mice that are applicable to fMRI using CryoProbe. RESULTS: A head-bar was surgically attached to the skull of a mouse that was then habituated to a mock fMRI-environment, two hours/day for eight days with physiological examinations of body-weight, fecal weight, electromyogram (EMG), and electrocardiogram. EMG power decreased with just one day of habituation, whereas heart rate decreased after at least seven days of habituation. Estimated head motions of awake mice during fMRI were significantly smaller than a voxel size. Unexpectedly, temporal SNR of fMRI signals for awake mice was higher than that for anesthetized mice held by a conventional method. Functional connectivity in the brain of both anesthetized and awake mice showed bilateral and unilateral networks. COMPARISON WITH EXISTING METHOD(S): fMRI using CryoProbe had been performed on anesthetized mice previously. Our method does not use anesthetics during habituation or fMRI. CONCLUSION: Our method would be beneficial for translational research using fMRI in mice and humans because human fMRI is typically performed without anesthetics.

Impacts of hydrophilic colanic acid on bacterial attachment to microfiltration membranes and subsequent membrane biofouling.

In order to examine the interactions between physicochemical properties of specific extracellular polymeric substances (EPS) and membrane biofouling, we investigated the impacts of hydrophilic colanic acid, as a model extracellular polysaccharide component, on initial bacterial attachment to different microfiltration (MF) membranes and membrane biofouling by using Escherichia coli strains producing different amounts of colanic acid. In a newly designed microtiter plate assay, the bacterial attachment by an E. coli strain RcsF(+), which produces massive amounts of colanic acid, decreased only to a hydrophobic membrane because the colanic acid made cell surfaces more hydrophilic, resulting in low cell attachment to hydrophobic membranes. The bench-scale cross-flow filtration tests followed by filtration resistance measurement revealed that RcsF(+) caused severe irreversible membrane fouling (i.e., pore-clogging), whereas less extracellular polysaccharide-producing strains caused moderate but reversible fouling to all membranes used in this study. Further cross-flow filtration tests indicated that colanic acid liberated in the bulk phase could rapidly penetrate pre-accumulated biomass layers (i.e., biofilms) and then directly clogged membrane pores. These results indicate that colanic acid, a hydrophilic extracellular polysaccharide, and possible polysaccharides with similar characteristics with colanic acid are considered as a major cause of severe irreversible membrane fouling (i.e., pore-clogging) regardless of biofilm formation (dynamic membrane).