Longitudinal manganese-enhanced magnetic resonance imaging of neural projections and activity

Centering cognitive neuroscience on task demands and generalization

Cognitive neuroscience seeks generalizable theories explaining the relationship between behavioral, physiological and mental states. In pursuit of such theories, we propose a theoretical and empirical framework that centers on understanding task demands and the mutual constraints they impose on behavior and neural activity. Task demands emerge from the interaction between an agent's sensory impressions, goals and behavior, which jointly shape the activity and structure of the nervous system on multiple spatiotemporal scales. Understanding this interaction requires multitask studies that vary more than one experimental component (for example, stimuli and instructions) combined with dense behavioral and neural sampling and explicit testing for generalization across tasks and data modalities. By centering task demands rather than mental processes that tasks are assumed to engage, this framework paves the way for the discovery of new generalizable concepts unconstrained by existing taxonomies, and moves cognitive neuroscience toward an action-oriented, dynamic and integrated view of the brain.

Mn-Anti-CTLA4-CREKA-Sericin Nanotheragnostics for Enhanced Magnetic Resonance Imaging and Tumor Immunotherapy

The integration of magnetic resonance imaging (MRI), cGAS-STING, and anti-CTLA-4 (aCTLA-4) based immunotherapy offers new opportunities for tumor precision therapy. However, the precise delivery of aCTLA-4 and manganese (Mn), an activator of cGAS, to tumors remains a major challenge for enhanced MRI and active immunotherapy. Herein, a theragnostic nanosphere Mn-CREKA-aCTLA-4-SS (MCCS) is prepared by covalently assembling Mn2+, silk sericin (SS), pentapeptide CREKA, and aCTLA-4. MCCS are stable with an average size of 160 nm and is almost negatively charged or neutral at pH 5.5/7.4. T1-weighted images showed MCCS actively targeted tumors to improve the relaxation rate r1 and contrast time of MRI. This studies demonstrated MCCS raises reactive oxygen species levels, activates the cGAS-STING pathway, stimulates effectors CD8+ and CD80+ T cells, reduces regulatory T cell numbers, and increases IFN-γ and granzyme secretion, thereby inducing tumor cells autophagy and apoptosis in vitro and in vivo. Also, MCCS are biocompatible and biosafe. These studies show the great potential of Mn-/SS-based integrative material MCCS for precision and personalized tumor nanotheragnostics.

Metabolomics-derived biomarkers for biosafety assessment of Gd-based nanoparticle magnetic resonance imaging contrast agents

With the rapid development of nanotechnology and biomedicine, numerous gadolinium (Gd)-based nanoparticle MRI contrast agents have been widely investigated. Due to the unique physicochemical properties of nanoparticles and the complexity of biological systems, the biosafety of Gd-based nanoparticle MRI contrast agents has been paid more and more attention. Herein, for the first time, we employed an ultra-high performance liquid chromatography-electrospray ionization quadrupole time-of-flight/mass spectrometry (UPLC-ESI-QTOF/MS)-based metabolomics approach to investigate the potential toxicity of Gd-based nanoparticle MRI contrast agents. In this work, NaGdF4 and PEG-NaGdF4 nanoparticles were successfully constructed and selected as the representative Gd-based nanoparticle MRI contrast agents for the metabolomics analysis. Based on the results of metabolomics, more metabolic biomarkers and pathways were identified in the NaGdF4 group than those in the PEG-NaGdF4 group. Careful analysis of these metabolic biomarkers and pathways suggested that NaGdF4 nanoparticles induced disturbance of pyrimidine and purine metabolism, inflammatory response, and kidney injury to a certain extent compared with PEG-NaGdF4 nanoparticles. These results indicated that Gd-based nanoparticle contrast agents modified with PEG had better biosafety. Additionally, it was demonstrated that the discovery of characteristic metabolomics biomarkers induced by nanoparticles would provide a new approach for biosafety assessment and stimulate the development of nanomedicine.

Harnessing axonal transport to map reward circuitry: Differing brain-wide projections from medial prefrontal cortical domains

Neurons project long axons that contact other distant neurons. Neurons in the medial prefrontal cortex project into the limbic system to regulate responses to reward or threat. Diminished neural activity in prefrontal cortex is associated with loss of executive function leading to drug use, yet the specific circuitry that mediate these effects is unknown. Different regions within the medial prefrontal cortex may project to differing limbic system nuclei. Here, we exploited the cell biology of intracellular membrane trafficking, fast axonal transport, to map projections from two adjacent medial prefrontal cortical regions. We used Mn(II), a calcium analog, to trace medial prefrontal cortical projections in the living animal by magnetic resonance imaging (MRI). Mn(II), a contrast agent for MRI, enters neurons through voltage-activated calcium channels and relies on kinesin-1 and amyloid-precursor protein to transport out axons to distal destinations. Aqueous MnCl2 together with fluorescent dextran (3--5 nL) was stereotactically injected precisely into two adjacent regions of the medial prefrontal cortex: anterior cingulate area (ACA) or infralimbic/prelimbic (IL/PL) region. Projections were traced, first live by manganese-enhanced MRI (MEMRI) at four time points in 3D, and then after fixation by microscopy. Data-driven unbiased voxel-wise statistical maps of aligned normalized MR images after either ACA or IL/PL injections revealed statistically significant progression of Mn(II) over time into deeper brain regions: dorsal striatum, globus pallidus, amygdala, hypothalamus, substantia nigra, dorsal raphe and locus coeruleus. Quantitative comparisons of these distal accumulations at 24 h revealed dramatic differences between ACA and IL/PL injection groups throughout the limbic system, and most particularly in subdomains of the hypothalamus. ACA projections targeted dorsomedial nucleus of the hypothalamus, posterior part of the periventricular region and mammillary body nuclei as well as periaqueductal gray, while IL/PL projections accumulated in anterior hypothalamic areas and lateral hypothalamic nuclei as well as amygdala. As hypothalamic subsegments relay CNS activity to the body, our results suggest new concepts about mind-body relationships and specific roles of distinct yet adjacent medial prefrontal cortical segments. Our MR imaging strategy, when applied to follow other cell biological processes in the living organism, will undoubtedly lead to an expanded perspective on how minute details of cellular processes influence whole body health and wellbeing.

In vivo labeling and quantitative imaging of neuronal populations using MRI

The study of neural circuits, which underlies perception, cognition, emotion, and behavior, is essential for understanding the mammalian brain, a complex organ consisting of billions of neurons. To study the structure and function of the brain, in vivo neuronal labeling and imaging techniques are crucial as they provide true physiological information that ex vivo methods cannot offer. In this paper, we present a new strategy for in vivo neuronal labeling and quantification using MRI. We demonstrate the efficacy of this method by delivering the oatp1a1 gene to the target neurons using rAAV2-retro virus. OATP1A1 protein expression on the neuronal membrane increased the uptake of a specific MRI contrast agent (Gd-EOB-DTPA), leading to hyperintense signals on T1W images of labeled neuronal populations. We also used dynamic contrast enhancement-based methods to obtain quantitative information on labeled neuronal populations in vivo.

Reconfiguration of brain-wide neural activity after early life adversity

Early life adversity (ELA) predisposes individuals to both physical and mental disorders lifelong. How ELA affects brain function leading to this vulnerability is under intense investigation. Research has begun to shed light on ELA effects on localized brain regions within defined circuits. However, investigations into brain-wide neural activity that includes multiple localized regions, determines relationships of activity between regions and identifies shifts of activity in response to experiential conditions is necessary. Here, we performed longitudinal manganese-enhanced magnetic resonance imaging (MEMRI) to image the brain in normally reared or ELA-exposed adults. Images were captured in the freely moving home cage condition, and short- and long-term after naturalistic threat. Images were analyzed with new computational methods, including automated segmentation and fractional activation or difference volumes. We found that neural activity was increased after ELA compared to normal rearing in multiple brain regions, some of which are involved in defensive and/or reward circuitry. Widely distributed patterns of neural activity, "brain states", and their dynamics after threat were altered with ELA. Upon acute threat, ELA-mice retained heightened neural activity within many of these regions, and new hyperactive responses emerged in monoaminergic centers of the mid- and hindbrain. Nine days after acute threat, heightened neural activity remained within locus coeruleus and increased within posterior amygdala, ventral hippocampus, and dorso- and ventromedial hypothalamus, while reduced activity emerged within medial prefrontal cortical regions (prelimbic, infralimbic, anterior cingulate). These results reveal that functional imbalances arise between multiple brain-systems which are dependent upon context and cumulative experiences after ELA.

Harnessing axonal transport to map reward circuitry: Differing brain-wide projections from medial forebrain domains

Neurons project long axons that contact other distant neurons. Projections can be mapped by hijacking endogenous membrane trafficking machinery by introducing tracers. To witness functional connections in living animals, we developed a tracer detectible by magnetic resonance imaging (MRI), Mn(II). Mn(II) relies on kinesin-1 and amyloid-precursor protein to travel out axons. Within 24h, projection fields of cortical neurons can be mapped brain-wide with this technology. MnCl2 was stereotactically injected either into anterior cingulate area (ACA) or into infralimbic/prelimbic (IL/PL) of medial forebrain (n=10-12). Projections were imaged, first by manganese-enhanced MRI (MEMRI) live, and then after fixation by microscopy. MR images were collected at 100μm isotropic resolution (~5 neurons) in 3D at four time points: before and at successive time points after injections. Images were preprocessed by masking non-brain tissue, followed by intensity scaling and spatial alignment. Actual injection locations, measured from post-injection MR images, were found to be 0.06, 0.49 and 0.84mm apart between cohorts, in R-L, A-P, and D-V directions respectively. Mn(II) enhancements arrived in hindbrains by 24h in both cohorts, while co-injected rhodamine dextran was not detectible beyond immediate subcortical projections. Data-driven unbiased voxel-wise statistical maps after ACA injections revealed significant progression of Mn(II) distally into deeper brain regions: globus pallidus, dorsal striatum, amygdala, hypothalamus, substantia nigra, dorsal raphe and locus coeruleus. Accumulation was quantified as a fraction of total volume of each segment containing significantly enhanced voxels (fractional accumulation volumes), and results visualized in column graphs. Unpaired t-tests between groups of brain-wide voxel-wise intensity profiling by either region of interest (ROI) measurements or statistical parametric mapping highlighted distinct differences in distal accumulation between injection sites, with ACA projecting to periaqueductal gray and IL/PL to basolateral amygdala (p<0.001 FDR). Mn(II) distal accumulations differed dramatically between injection groups in subdomains of the hypothalamus, with ACA targeting dorsal medial, periventricular region and mammillary body nuclei, while IL/PL went to anterior hypothalamic areas and lateral hypothalamic nuclei. Given that these hypothalamic subsegments communicate activity in the central nervous system to the body, these observations describing distinct forebrain projection fields will undoubtedly lead to newer insights in mind-body relationships.