3D inversion recovery ultrashort echo time MRI can detect demyelination in cuprizone-treated mice.

Purpose: To test the ability of inversion-recovery ultrashort echo time (IR-UTE) MRI to directly detect demyelination in mice using a standard cuprizone mouse model. Methods: Non-aqueous myelin protons have ultrashort T2s and are "invisible" with conventional MRI sequences but can be detected with UTE sequences. The IR-UTE sequence uses an adiabatic inversion-recovery preparation to suppress the long T2 water signal so that the remaining signal is from the ultrashort T2 myelin component. In this study, eight 8-week-old C57BL/6 mice were fed cuprizone (n = 4) or control chow (n = 4) for 5 weeks and then imaged by 3D IR-UTE MRI. The differences in IR-UTE signal were compared in the major white matter tracts in the brain and correlated with the Luxol Fast Blue histochemical marker of myelin. Results: IR-UTE signal decreased in cuprizone-treated mice in white matter known to be sensitive to demyelination in this model, such as the corpus callosum, but not in white matter known to be resistant to demyelination, such as the internal capsule. These findings correlated with histochemical staining of myelin content. Conclusions: 3D IR-UTE MRI was sensitive to cuprizone-induced demyelination in the mouse brain, and is a promising noninvasive method for measuring brain myelin content.

Control of the activity of CAR-T cells within tumours via focused ultrasound.

Focused ultrasound can deliver energy safely and non-invasively into tissues at depths of centimetres. Here we show that the genetics and cellular functions of chimeric antigen receptor T cells (CAR-T cells) within tumours can be reversibly controlled by the heat generated by short pulses of focused ultrasound via a CAR cassette under the control of a promoter for the heat-shock protein. In mice with subcutaneous tumours, locally injected T cells with the inducible CAR and activated via focused ultrasound guided by magnetic resonance imaging mitigated on-target off-tumour activity and enhanced the suppression of tumour growth, compared with the performance of non-inducible CAR-T cells. Acoustogenetic control of the activation of engineered T cells may facilitate the design of safer cell therapies.

DTI-identified microstructural changes in the gray matter of mice overexpressing CRF in the forebrain.

Increased corticotroping releasing factor (CRF) contributes to brain circuit abnormalities associated with stress-related disorders including posttraumatic stress disorder. However, the causal relationship between CRF hypersignaling and circuit abnormalities associated with stress disorders is unclear. We hypothesized that increased CRF exposure induces changes in limbic circuit morphology and functions. An inducible, forebrain-specific overexpression of CRF (CRFOE) transgenic mouse line was used to longitudinally investigate its chronic effects on behaviors and microstructural integrity of several brain regions. Behavioral and diffusion tensor imaging studies were performed before treatment, after 3-4 wks of treatment, and again 3 mo after treatment ended to assess recovery. CRFOE was associated with increased perseverative movements only after 3 wks of treatment, as well as reduced fractional anisotropy at 3 wks in the medial prefrontal cortex and increased fractional anisotropy in the ventral hippocampus at 3 mo compared to the control group. In the dorsal hippocampus, mean diffusivity was lower in CRFOE mice both during and after treatment ended. Our data suggest differential response and recovery patterns of cortical and hippocampal subregions in response to CRFOE. Overall these findings support a causal relationship between CRF hypersignaling and microstructural changes in brain regions relevant to stress disorders.

Global chemical effects of the microbiome include new bile-acid conjugations.

A mosaic of cross-phylum chemical interactions occurs between all metazoans and their microbiomes. A number of molecular families that are known to be produced by the microbiome have a marked effect on the balance between health and disease1-9. Considering the diversity of the human microbiome (which numbers over 40,000 operational taxonomic units10), the effect of the microbiome on the chemistry of an entire animal remains underexplored. Here we use mass spectrometry informatics and data visualization approaches11-13 to provide an assessment of the effects of the microbiome on the chemistry of an entire mammal by comparing metabolomics data from germ-free and specific-pathogen-free mice. We found that the microbiota affects the chemistry of all organs. This included the amino acid conjugations of host bile acids that were used to produce phenylalanocholic acid, tyrosocholic acid and leucocholic acid, which have not previously been characterized despite extensive research on bile-acid chemistry14. These bile-acid conjugates were also found in humans, and were enriched in patients with inflammatory bowel disease or cystic fibrosis. These compounds agonized the farnesoid X receptor in vitro, and mice gavaged with the compounds showed reduced expression of bile-acid synthesis genes in vivo. Further studies are required to confirm whether these compounds have a physiological role in the host, and whether they contribute to gut diseases that are associated with microbiome dysbiosis.

Spatial encoding in primate hippocampus during free navigation.

The hippocampus comprises two neural signals-place cells and θ oscillations-that contribute to facets of spatial navigation. Although their complementary relationship has been well established in rodents, their respective contributions in the primate brain during free navigation remains unclear. Here, we recorded neural activity in the hippocampus of freely moving marmosets as they naturally explored a spatial environment to more explicitly investigate this issue. We report place cells in marmoset hippocampus during free navigation that exhibit remarkable parallels to analogous neurons in other mammalian species. Although θ oscillations were prevalent in the marmoset hippocampus, the patterns of activity were notably different than in other taxa. This local field potential oscillation occurred in short bouts (approximately .4 s)-rather than continuously-and was neither significantly modulated by locomotion nor consistently coupled to place-cell activity. These findings suggest that the relationship between place-cell activity and θ oscillations in primate hippocampus during free navigation differs substantially from rodents and paint an intriguing comparative picture regarding the neural basis of spatial navigation across mammals.

Awake Mouse Imaging: From Two-Photon Microscopy to Blood Oxygen Level-Dependent Functional Magnetic Resonance Imaging.

BACKGROUND: Functional magnetic resonance imaging (fMRI) in awake behaving mice is well positioned to bridge the detailed cellular-level view of brain activity, which has become available owing to recent advances in microscopic optical imaging and genetics, to the macroscopic scale of human noninvasive observables. However, though microscopic (e.g., two-photon imaging) studies in behaving mice have become a reality in many laboratories, awake mouse fMRI remains a challenge. Owing to variability in behavior among animals, performing all types of measurements within the same subject is highly desirable and can lead to higher scientific rigor. METHODS: We demonstrated blood oxygenation level-dependent fMRI in awake mice implanted with long-term cranial windows that allowed optical access for microscopic imaging modalities and optogenetic stimulation. We started with two-photon imaging of single-vessel diameter changes (n = 1). Next, we implemented intrinsic optical imaging of blood oxygenation and flow combined with laser speckle imaging of blood flow obtaining a mesoscopic picture of the hemodynamic response (n = 16). Then we obtained corresponding blood oxygenation level-dependent fMRI data (n = 5). All measurements could be performed in the same mice in response to identical sensory and optogenetic stimuli. RESULTS: The cranial window did not deteriorate the quality of fMRI and allowed alternation between imaging modalities in each subject. CONCLUSIONS: This report provides a proof of feasibility for multiscale imaging approaches in awake mice. In the future, this protocol could be extended to include complex cognitive behaviors translatable to humans, such as sensory discrimination or attention.

Demonstration of Non-Gaussian Restricted Diffusion in Tumor Cells Using Diffusion Time-Dependent Diffusion-Weighted Magnetic Resonance Imaging Contrast.

The diffusion-weighted magnetic resonance imaging (DWI) technique enables quantification of water mobility for probing microstructural properties of biological tissue and has become an effective tool for collecting information about the underlying pathology of cancerous tissue. Measurements using multiple b-values have indicated biexponential signal attenuation, ascribed to "fast" (high ADC) and "slow" (low ADC) diffusion components. In this empirical study, we investigate the properties of the diffusion time (Δ)-dependent components of the diffusion-weighted (DW) signal in a constant b-value experiment. A xenograft gliobastoma mouse was imaged using Δ = 11 ms, 20 ms, 40 ms, 60 ms, and b = 500-4000 s/mm(2) in intervals of 500 s/mm(2). Data were corrected for EPI distortions, and the Δ-dependence on the DW-signal was measured within three regions of interest [intermediate- and high-density tumor regions and normal-appearing brain (NAB) tissue regions]. In this study, we verify the assumption that the slow decaying component of the DW-signal is non-Gaussian and dependent on Δ, consistent with restricted diffusion of the intracellular space. As the DW-signal is a function of Δ and is specific to restricted diffusion, manipulating Δ at constant b-value (cb) provides a complementary and direct approach for separating the restricted from the hindered diffusion component. We found that Δ-dependence is specific to the tumor tissue signal. Based on an extended biexponential model, we verified the interpretation of the diffusion time-dependent contrast and successfully estimated the intracellular restricted ADC, signal volume fraction, and cell size within each ROI.

Microstructural changes to the brain of mice after methamphetamine exposure as identified with diffusion tensor imaging.

Methamphetamine (METH) is an addictive psychostimulant inducing neurotoxicity. Human magnetic resonance imaging and diffusion tensor imaging (DTI) of METH-dependent participants find various structural abnormities. Animal studies demonstrate immunohistochemical changes in multiple cellular pathways after METH exposure. Here, we characterized the long-term effects of METH on brain microstructure in mice exposed to an escalating METH binge regimen using in vivo DTI, a methodology directly translatable across species. Results revealed four patterns of differential fractional anisotropy (FA) and mean diffusivity (MD) response when comparing METH-exposed (n=14) to saline-treated mice (n=13). Compared to the saline group, METH-exposed mice demonstrated: 1) decreased FA with no change in MD [corpus callosum (posterior forceps), internal capsule (left), thalamus (medial aspects), midbrain], 2) increased MD with no change in FA [posterior isocortical regions, caudate-putamen, hypothalamus, cerebral peduncle, internal capsule (right)], 3) increased FA with decreased MD [frontal isocortex, corpus callosum (genu)], and 4) increased FA with no change or increased MD [hippocampi, amygdala, lateral thalamus]. MD was negatively associated with calbindin-1 in hippocampi and positively with dopamine transporter in caudate-putamen. These findings highlight distributed and differential METH effects within the brain suggesting several distinct mechanisms. Such mechanisms likely change brain tissue differentially dependent upon neural location.

Looking forward in records of young adults convicted of sexual homicide, rape, or molestation as youth: risks for reoffending.

To assess the risks predicting reoffense, 223 Rapists (M age = 14.2 yr., SD = 1.5; 25 girls, 198 boys) were matched with 223 Nonviolent Delinquents; risks were analyzed using logistic regression. The one predictor was prior court contacts (OR = 1.55e+12; AUC = .99, 95% CI = .98-.99). 223 Molesters were similarly matched with 223 Nonviolent Delinquents; this comparison yielded three predictors: previous court contacts (OR = 4.55e+23), poorer executive function (OR = 2.01), and lower social maturity (OR = .97; AUC = .98, 95% CI = .97-.99). Records for all cases (now M age = 24.2 yr., SD = 1.4) were reviewed forward 10 years and youth were classified into groups: Sexual Homicidal (1%, n = 7), Delinquent Rapists Later Adult Rapists (11%, n = 73), Delinquent Rapists (21%, n = 144), Delinquent Molesters Later Adult Molesters (10%, n = 69), Delinquent Molesters (23%, n = 153), Nonviolent Delinquent Later Nonviolent Adult Criminals (7%, n = 45), and Nonviolent Delinquents (27%, n = 178). Comparison of Sexual Homicidal cases (n = 7) with their matched Controls (n = 7) yielded one predictor, poorer executive function (AUC = .89, 95% CI = .71-.93). When Sexual Homicidal cases were matched with Nonviolent Delinquents, predictors were low social maturity and prior court contacts (AUC = .81, 95% CI = .64-.93).

Helix periodicity, topology, and dynamics of membrane-associated alpha-synuclein.

The protein alpha-Synuclein (aS) is a synaptic vesicle-associated regulator of synaptic strength and dopamine homeostasis with a pathological role in Parkinson's disease. The normal function of aS depends on a membrane-associated conformation that is adopted upon binding to negatively charged lipid surfaces. Previously we found that the membrane-binding domain of aS is helical and suggested that it may exhibit an unusual structural periodicity. Here we present a study of the periodicity, topology, and dynamics of detergent micelle-bound aS using paramagnetic spin labels embedded in the micelle or attached to the protein. We show that the helical region of aS completes three full turns every 11 residues, demonstrating the proposed 11/3 periodicity. We also find that the membrane-binding domain is partially buried in the micelle surface and bends toward the hydrophobic interior, but does not traverse the micelle. Deeper submersion of certain regions within the micelle, including the unique lysine-free sixth 11-residue repeat, is observed and may be functionally important. There are no long-range tertiary contacts within this domain, indicating a highly extended configuration. The backbone dynamics of the micelle-bound region are relatively uniform with a slight decrease in flexibility observed toward the C-terminal end. These results clarify the topological features of aS bound to membrane-mimicking detergent micelles, with implications for aS function and pathology.

Effects of Parkinson's disease-linked mutations on the structure of lipid-associated alpha-synuclein.

Alpha-synuclein (alphaS) is a lipid-binding synaptic protein of unknown function that is found in an aggregated amyloid fibril form in the intraneuronal Lewy body deposits that are a defining characteristic of Parkinson's disease (PD). Although intrinsically unstructured when free in solution, alphaS adopts a highly helical conformation in association with lipid membranes or membrane mimetic detergent micelles. Two mutations in the alphaS gene have been linked to early onset autosomal dominant hereditary forms of PD, and have been shown to affect the aggregation kinetics of the protein in vitro. We have used high-resolution NMR spectroscopy, circular dichroism, and limited proteolysis to investigate the effects of these PD-linked mutations on the helical structure adopted by alphaS in the lipid or detergent micelle-bound form. We show that neither the A53T nor the A30P mutation has a significant effect on the structure of the folded protein, although the A30P mutation may cause a minor perturbation in the helical structure around the site of the mutation. The A30P, but not the A53T, mutation also appears to decrease the affinity of the protein for lipid surfaces, possibly by perturbing the nascent helical structure of the free protein. The potential implications of these results for the role of alphaS in PD are discussed.

A structural and functional role for 11-mer repeats in alpha-synuclein and other exchangeable lipid binding proteins.

We have used NMR spectroscopy and limited proteolysis to characterize the structural properties of the Parkinson's disease-related protein alpha-synuclein in lipid and detergent micelle environments. We show that the lipid or micelle surface-bound portion of the molecule adopts a continuously helical structure with a single break. Modeling alphaS as an ideal alpha-helix reveals a hydrophobic surface that winds around the helix axis in a right-handed fashion. This feature is typical of 11-mer repeat containing sequences that adopt right-handed coiled coil conformations. In order to bind a flat or convex lipid surface, however, an unbroken helical alphaS structure would need to adopt an unusual, slightly unwound, alpha11/3 helix conformation (three complete turns per 11 residues). The break we observe in the alphaS helix may allow the protein to avoid this unusual conformation by adopting two shorter stretches of typical alpha-helical structure. However, a quantitative analysis suggests the possibility that the alpha11/3 conformation may in fact exist in lipid-bound alphaS. We discuss how structural features of helical 11-mer repeats could play a role in the reversible lipid binding function of alpha-synuclein and generalize this argument to include the 11-mer repeat-containing apolipoproteins, which also require the ability to release readily from lipid surfaces. A search of protein sequence databases confirms that synuclein-like 11-mer repeats are present in other proteins that bind lipids reversibly and predicts such a role for a number of hypothetical proteins of unknown function.