Homologous organization of cerebellar pathways to sensory, motor, and associative forebrain.

Cerebellar outputs take polysynaptic routes to reach the rest of the brain, impeding conventional tracing. Here, we quantify pathways between the cerebellum and forebrain by using transsynaptic tracing viruses and a whole-brain analysis pipeline. With retrograde tracing, we find that most descending paths originate from the somatomotor cortex. Anterograde tracing of ascending paths encompasses most thalamic nuclei, especially ventral posteromedial, lateral posterior, mediodorsal, and reticular nuclei. In the neocortex, sensorimotor regions contain the most labeled neurons, but we find higher densities in associative areas, including orbital, anterior cingulate, prelimbic, and infralimbic cortex. Patterns of ascending expression correlate with c-Fos expression after optogenetic inhibition of Purkinje cells. Our results reveal homologous networks linking single areas of the cerebellar cortex to diverse forebrain targets. We conclude that shared areas of the cerebellum are positioned to provide sensory-motor information to regions implicated in both movement and nonmotor function

Serial two-photon tomography for automated ex vivo mouse brain imaging

Here we describe an automated method, named serial two-photon (STP) tomography, that achieves high-throughput fluorescence imaging of mouse brains by integrating two-photon microscopy and tissue sectioning. STP tomography generates high-resolution datasets that are free of distortions and can be readily warped in three dimensions, for example, for comparing multiple anatomical tracings. This method opens the door to routine systematic studies of neuroanatomy in mouse models of human brain disorders

Hippocampal brain-derived neurotrophic factor determines recruitment of anatomically connected networks after stress in diabetic mice

Diabetes increases adrenal steroids in humans and animal models, but potential interactions with psychological stress remain poorly understood. Diabetic rodents exhibit anxiety and reductions in hippocampal brain-derived neurotrophic factor (BDNF) expression, and these studies investigated whether loss of BDNF-driven hippocampal activity promotes anxiety and disinhibits the HPA axis. Mice with genetic obesity and diabetes (db/db) received intrahippocampal injections of lentivirus for BDNF overexpression (db/db-BDNFOE), and Wt mice received lentiviral constructs for BDNF knockdown (Wt-BDNFKD). Behavioral anxiety, and glucocorticoid responses to acute restraint were compared with mice that received a fluorescent reporter (Wt-GFP, db/db-GFP). These experiments revealed that changes in hippocampal BDNF were necessary and sufficient for behavioral anxiety and HPA axis disinhibition. To examine patterns of stress-induced regional activity, we used algorithmic detection of cFos and automated segmentation of forebrain regions to generate maps of functional covariance, which were subsequently aligned with anatomical connectivity weights from the Brain Architecture Management database. db/db-GFP mice exhibited reduced activation of the hippocampal ventral subiculum (vSub) and anterior bed nucleus of stria terminalis (aBNST), and increases in the paraventricular hypothalamus (PVH), relative to Wt-GFP. BDNFKD recapitulated this pattern in Wt mice, and BDNFOE normalized activation of the vSub>aBNST>PVH pathway in db/db mice. Analysis of forebrain activation revealed largely overlapping patterns of network disruption in db/db-GFP and Wt-BDNFKD mice, implicating BDNF-driven hippocampal activity as a determinant of stress vulnerability in both the intact and diabetic brain. This article is protected by copyright. All rights reserved

Reconstructing neuronal anatomy from whole-brain images

Reconstructing multiple molecularly defined neurons from individual brains and across multiple brain regions can reveal organizational principles of the nervous system. However, high resolution imaging of the whole brain is a technically challenging and slow process. Recently, oblique light sheet microscopy has emerged as a rapid imaging method that can provide whole brain fluorescence microscopy at a voxel size of 0.4\times 0.4\times 2.5\mu \mathrm{m}^{3}. On the other hand, complex image artifacts due to whole-brain coverage produce apparent discontinuities in neuronal arbors. Here, we present connectivity-preserving methods and data augmentation strategies for supervised learning of neuroanatomy from light microscopy using neural networks. We quantify the merit of our approach by implementing an end-to-end automated tracing pipeline. Lastly, we demonstrate a scalable, distributed implementation that can reconstruct the large datasets that sub-micron whole-brain images produce. © 2019 IEEE

A brain network basis of Fragile X syndrome behavioral penetrance determined by X chromosome inactivation in female mice

X-chromosome inactivation (XCI) in females is vital for normal brain function and cognition, as many X-linked genetic mutations lead to mental retardation and autism spectrum disorders, such as the fragile X syndrome (FXS). However, the degree by which XCI regulates disease presentation has been poorly investigated. To study this regulation in the mouse, here we quantified the brainwide composition of active-XC cells at single cell resolution using an X-linked MECP2-EGFP allele with known parent-of-origin. We present evidence that whole-brains, including all regions, on average favor maternal XC-active cells by 20%, or 8 million cells. This bias was conserved in heterozygous FXS mutant mice, which also corresponded to disease penetrance in maternal but not paternal FMR1 null mice. To localize the physical source of behavioral penetrance, brain-wide correlational screens successfully mapped mouse performance to cell densities in putative sensorimotor (e.g. sensory hindbrain, thalamus, globus pallidus) and sociability (e.g. visual/entorhinal cortices, bed nucleus stria terminalis, medial preoptic area) behavioral circuits of the open field sensorimotor and 3-chamber sociability assays, respectively. Overall, 50%/50% healthy/mutant cell density ratios in these brain networks were required for disease presentation in each behavior. These results suggest female X-linked behavioral penetrance of disease is regulated at the distributed level of mutant cell density in behavioral circuits, which is set by XCI that is subject to parent-of-origin effects. This work provides a novel explanation behind the broad and varied behavioral phenotypes commonly featured in female patients debilitated with X-linked mental disorders and may offer new entry points for behavioral therapeutics