Towards reliable reconstruction of the mouse brain corticothalamic connectivity using diffusion MRI

Sex-specific signatures of GLP-1 and amylin on resting state brain activity and functional connectivity in awake rats

Gut-produced glucagon-like peptide-1 (GLP-1) and pancreas-made amylin robustly reduce food intake by directly or indirectly affecting brain activity. While for both peptides a direct action in the hindbrain and the hypothalamus is likely, few studies examined their impact on whole brain activity in rodents and did so evaluating male rodents under anesthesia. However, both sex and anesthesia may significantly alter the influence of feeding controlling molecules on brain activity. Therefore, we investigated the effect of GLP-1 and amylin on brain activity and functional connectivity (FC) in awake adult male and female rats using resting-state functional magnetic resonance imaging (rsfMRI). We further examined the relationship between the altered brain activity or connectivity and subsequent food intake in response to amylin or GLP-1. We observed sex divergent effects of amylin and GLP-1 on the brain activity and FC patterns. Most importantly correlation analysis between FC and feeding behavior revealed that different brain areas potentially drive reduced food intake in male and female rats. Our findings underscore the distributed and distinctly sex divergent neural network engaged by each of these anorexic peptides and suggest that different brain areas may be the primary drivers of the feeding outcome in male and female rats. Moreover, prominent activity and connectivity alterations observed in brain areas not typically associated with feeding behavior in both sexes may either indicate novel feeding centers or alternatively suggest the involvement of these substances in behaviors beyond feeding and metabolism. The latter question is of potential translational significance as analogues of both amylin and GLP-1 are clinically utilized.

The Duke Mouse Brain Atlas: MRI and light sheet microscopy stereotaxic atlas of the mouse brain

Atlases of the brain are critical resources that make it possible to share data in a common reference frame. Unexpectedly, there is no three-dimensional (3D) stereotaxic atlas of the mouse brain that provides whole brain coverage at macro to single-cell levels. Diffusion tensor images from five perfusion-fixed (in skull) specimens were acquired at 15 micrometers, the highest resolution ever reported. Diffusion tensor imaging yields multiple 3D volumes, each of which highlights unique cytoarchitecture. The averages were mapped into micro-computed tomography of the mouse skull to create external landmarks (bregma and lambda). Light sheet images of the same brains were coregistered, providing cell maps in the same stereotaxic space. The Allen Reference Atlas was registered to the volume to correct the geometric distortion in that atlas and bring it into the stereotaxic space. The resulting multiscalar (13 terabytes) atlas provides a common spatial framework to anneal data across molecular, structural, and functional studies of mice.

Cerebellar output neurons can impair non-motor behaviors by altering development of extracerebellar connectivity

The capacity of the brain to compensate for insults during development depends on the type of cell loss, whereas the consequences of genetic mutations in the same neurons are difficult to predict. We reveal powerful compensation from outside the mouse cerebellum when the excitatory cerebellar output neurons are ablated embryonically and demonstrate that the main requirement for these neurons is for motor coordination and not basic learning and social behaviors. In contrast, loss of the homeobox transcription factors Engrailed1/2 (EN1/2) in the cerebellar excitatory lineage leads to additional deficits in adult learning and spatial working memory, despite half of the excitatory output neurons being intact. Diffusion MRI indicates increased thalamo-cortico-striatal connectivity in En1/2 mutants, showing that the remaining excitatory neurons lacking En1/2 exert adverse effects on extracerebellar circuits regulating motor learning and select non-motor behaviors. Thus, an absence of cerebellar output neurons is less disruptive than having cerebellar genetic mutations.

RS2-Net: An end-to-end deep learning framework for rodent skull stripping in multi-center brain MRI

Skull stripping is a crucial preprocessing step in magnetic resonance imaging (MRI), where experts manually create brain masks. This labor-intensive process heavily relies on the annotator's expertise, as automation faces challenges such as low tissue contrast, significant variations in image resolution, and blurred boundaries between the brain and surrounding tissues, particularly in rodents. In this study, we have developed a lightweight framework based on Swin-UNETR to automate the skull stripping process in MRI scans of mice and rats. The primary objective of this framework is to eliminate the need for preprocessing, reduce the workload, and provide an out-of-the-box solution capable of adapting to various MRI image resolutions. By employing a lightweight neural network, we aim to lower the performance requirements of the framework. To validate the effectiveness of our approach, we trained and evaluated the network using publicly available multi-center data, encompassing 1,037 rodents and 1,142 images from 89 centers, resulting in a preliminary mean Dice coefficient of 0.9914. The framework, data, and pre-trained models can be found on the following link: https://github.com/VitoLin21/Rodent-Skull-Stripping.

Cerebellar output neurons impair non-motor behaviors by altering development of extracerebellar connectivity

The capacity of the brain to compensate for insults during development depends on the type of cell loss, whereas the consequences of genetic mutations in the same neurons are difficult to predict. We reveal powerful compensation from outside the cerebellum when the excitatory cerebellar output neurons are ablated embryonically and demonstrate that the minimum requirement for these neurons is for motor coordination and not learning and social behaviors. In contrast, loss of the homeobox transcription factors Engrailed1/2 (EN1/2) in the cerebellar excitatory lineage leads to additional deficits in adult learning and spatial working memory, despite half of the excitatory output neurons being intact. Diffusion MRI indicates increased thalamo-cortico-striatal connectivity in En1/2 mutants, showing that the remaining excitatory neurons lacking En1/2 exert adverse effects on extracerebellar circuits regulating motor learning and select non-motor behaviors. Thus, an absence of cerebellar output neurons is less disruptive than having cerebellar genetic mutations.

Early adversity causes sex-specific deficits in perforant pathway connectivity and contextual memory in adolescent mice

BACKGROUND

Early life adversity impairs hippocampal development and function across diverse species. While initial evidence indicated potential variations between males and females, further research is required to validate these observations and better understand the underlying mechanisms contributing to these sex differences. Furthermore, most of the preclinical work in rodents was performed in adult males, with only few studies examining sex differences during adolescence when such differences appear more pronounced. To address these concerns, we investigated the impact of limited bedding (LB), a mouse model of early adversity, on hippocampal development in prepubescent and adolescent male and female mice.

METHODS

RNA sequencing, confocal microscopy, and electron microscopy were used to evaluate the impact of LB and sex on hippocampal development in prepubescent postnatal day 17 (P17) mice. Additional studies were conducted on adolescent mice aged P29-36, which included contextual fear conditioning, retrograde tracing, and ex vivo diffusion magnetic resonance imaging (dMRI).

RESULTS

More severe deficits in axonal innervation and myelination were found in the perforant pathway of prepubescent and adolescent LB males compared to LB female littermates. These sex differences were due to a failure of reelin-positive neurons located in the lateral entorhinal cortex (LEC) to innervate the dorsal hippocampus via the perforant pathway in males, but not LB females, and were strongly correlated with deficits in contextual fear conditioning.

CONCLUSIONS

LB impairs the capacity of reelin-positive cells located in the LEC to project and innervate the dorsal hippocampus in LB males but not female LB littermates. Given the critical role that these projections play in supporting normal hippocampal function, a failure to establish proper connectivity between the LEC and the dorsal hippocampus provides a compelling and novel mechanism to explain the more severe deficits in myelination and contextual freezing found in adolescent LB males.

Open-source versatile 3D-print animal conditioning platform design for in vivo preclinical brain imaging in awake mice and anesthetized mice and rats

Proper animal conditioning is a key factor in the quality and success of preclinical neuroimaging applications. Here, we introduce an open-source easy-to-modify multimodal 3D printable design for rodent conditioning for magnetic resonance imaging (MRI) or other imaging modalities. Our design can be used for brain imaging in anesthetized or awake mice, and in anesthetized rats. We show ease of use and reproducibility of subject conditioning with anatomical T2-weighted imaging for both mice and rats. We also demonstrate the application of our design for awake functional MRI in mice using both visual evoked potential and olfactory stimulation paradigms. In addition, using a combined MRI, positron emission tomography and X-ray computed tomography experiment, we demonstrate that our proposed cradle design can be utilized for multiple imaging modalities.