Keywords: Small Animals, Neuroscience, Neurovascular coupling;Excitatory neurons;Inhibitory neurons;Anesthesia

Motivation: Understanding hemodynamic activity is essential for blood-based brain mapping techniques like fMRI.

Goal(s): Many studies have demonstrated that excitatory activity leads to an increase in hemodynamic response. However, how inhibitory neurons regulate the brain blood’s supply is less understood. Also, how hemodynamic response is modulated by brain status induced by different anesthetic is still unclear. 

Approach: To investigate that, we used optical intrinsic signal imaging to investigate the roles of excitatory and inhibitory activity under awake and different anesthetic conditions.

Results: Our findings revealed that different conditions not only shape the response time and peak change but also causes different hemodynamic response.

Impact: We investigated the hemodynamic response of excitatory and inhibitory neurons by optogenetic stimulation under awake and 3 commonly used anesthetics. Our study may have an impact on investigating neurovascular coupling in different brain conditions.

Keywords: Small Animals, Preclinical

Motivation: Zero-echo time (ZTE) sequence reduces susceptibility artifacts compared to echo planar imaging (EPI). However, the feasibility of ZTE for functional MRI (fMRI) has not been fully investigated.

Goal(s): Our goal was to assess the feasibility of ZTE for fMRI. 

Approach: Time-course of ZTE, gradient echo (GE)-EPI, and spin echo (SE)-EPI signal changes by somatosensory stimulation was investigated. The functional connectivity in resting state ZTE, GE-EPI, SE-EPI was also compared.

Results: The results indicate that ZTE is useful for fMRI.

Impact: ZTE sequences realize the fMRI that is robust to susceptibility artifacts.

Keywords: Large Animals, Nonhuman Primates, Preclinical, animal models

Motivation: Functional magnetic resonance imaging is increasingly used to study brain function and cognition in domestic dogs.

Goal(s): The objective of this study was to acquire the high-quality fMRI data which dogs can be trained to remain awake and still inside MRI scanners and detect the pathway for dog’s face processing.

Approach: We use a combination of simulated and real MRI environments to train awake dogs. A visual stimulation paradigm with block design was used to compare activity elicited by human faces against objects.

Results: We successfully detect the activation of human faces against scramble objects in occipitalis, ectomarginalis, and ectosylvius medius.

Impact: This study provides a process for training dogs for fMRI acquisition while awake and introduces the temporal cortex as candidate to process human faces and dog faces.

Keywords: Neurofluids, Brain, Glymphatic System

Motivation: This study investigates the glymphatic function in awake vs. anesthetized mice by means of diffusion-weighted (DW) MRI.

Goal(s): Application of developed ‘silent’ DW-MRI protocol is presented for comparison of awake and anesthetized mice under ketamine-xylazine (K/X), and isoflurane. 

Approach:  In total, n=17 C57BL/6 mice were habituated to awake MRI setup, and successfully underwent DW-MRI with monitored body temperature and respiratory rate.

Results: Results showed that brain water mobility in awake mice was consistent, while K/X and isoflurane affected both slow and fast MR diffusivity measures differently. Awake DW-MRI offers a promising alternative to MRI under anesthesia, promoting increased biological relevance and translational potential.

Impact: This research on glymphatic function using DW-MRI underscores the importance of non-invasive MRI in awake mice, emphasizing anesthesia's impact on physiological stability. It highlights the translational potential of awake DW-MRI and is of importance to neuroscientific and biomedical research communities.

Keywords: Small Animals, Velocity & Flow, Magnetic resonance velocity mapping; Phase contrast; Velocity; Rat.

Motivation: Several human cerebral diseases are associated to neurofluids dynamics alterations and continue to require preclinical research studies. Rat models were widely used to understand these diseases but its cerebral hemodynamic is not fully elucidated. Phase contrast (PCMRI) allows noninvasive quantification of blood flow dynamics.

Goal(s): Our goal was to investigate both cerebral arterial and venous sinuses flows in rats.

Approach: Twelve Sprague-Dawley rats underwent a 7T preclinical MRI. PCMRI quantified blood flows dynamics in the internal/external carotid arteries, basilar artery and transverse sinuses during cardiac cycle.

Results: We obtained physiological references of cerebral blood flows parameters for these main cerebral vessels in rats.

Impact: This study highlights the potential of PCMRI to investigate cerebral blood flows dynamics in rats.  These findings may be important to study neurofluids dynamics interactions, pressure and compliance, to better understand human idiopathic pathologies such as hydrocephalus and intracranial hypertension.

Keywords: Small Animals, Elastography, sex differences, estrous, rat

Motivation: In rodent studies, the number of spines on hippocampal CA1 neurons decreases from proestrus to estrus, and complimentary reductions to hippocampal volume are observed in rodents and humans. It remains unknown if estrous-related changes to tissue microstructure alter the mechanical properties of CA1.

Goal(s): Evaluate the mechanical properties of CA1 between proestrus and estrus in the adult rat brain.

Approach: A novel rat Magnetic Resonance Elastography (MRE) protocol, measuring tissue deformation to determine stiffness and viscosity, was used to identify changes to the mechanical properties of CA1.

Results: CA1 stiffness increases between proestrus and estrus phases in female rats.

Impact: Results from this longitudinal study show that the stiffness of the hippocampal CA1 subregion increases between proestrus and estrus phases within-rat. We did not discover any changes to whole brain biomechanics between proestrus and estrus within-rat, consistent with the literature.

Keywords: Biology, Models, Methods, Aging, elastography

Motivation: The biomechanical signature of the aging brain and its correlation with the underlying microstructure, is poorly understood.

Goal(s): To systematically analyze the global and regional biomechanical properties of the brain during aging.

Approach: We investigated the in vivo biomechanical progression of the female mouse brain over an age range of 6 to 18 months using multifrequency MR elastography.

Results: Highly resolved elastographic atlases of the mouse brain at different ages were generated. Global and regional analysis revealed softening and reduced viscosity as dominating patters of biomechanical changes related to the structural variations of the aging brain.

Impact: This study demonstrated the use of MR elastography to track the biomechanical changes in the brains of aging healthy mice. Our study revealed softening and increased viscosity as biomechanical signature of the aging brain.

Keywords: Preclinical Image Analysis, Spectroscopy, animals, aging, spectroscopy, treatment, Rho GTPases

Motivation: RhoGTPases are involved in the pathogenesis of neurodegenerative and neurodevelopmental diseases, playing a key role in synaptic plasticity.

Goal(s): The aim is to evaluate the involvement of RhoGTPases on ageing processes, assessing effects of RhoGTPases modulation on behavior and brain metabolism (by MRS) on a healthy aging mouse model.

Approach: We pharmacologically modulated RhoGTPases pathways by administering fasudil or CNF1 in mice. Animals are subjected to behavioral tests and to MRI/MRS experiments in frontal cortex, hippocampus and cerebellum.

Results: Young mice showed apparent greater anxiolytic effect respect to old mice. We observed also age- differences in the metabolism in response to both treatments.

Impact: Dysregulation of the RhoGTPase pathway leads to: oxidative stress, inflammation, alterations in energy metabolism and reduced synaptic transmission. RhoGTPase pathway is involved in the pathogenesis of neurodegenerative diseases; RhoGTPases are here proposed as an innovative pharmacological target for their treatment.

Keywords: Neurofluids, Neurofluids, Glymphatic System

Motivation: The glymphatic system’s role in metabolic waste removal in the brain is crucial. Impairment of the flow of cerebrospinal fluid (CSF) and interstitial fluid (ISF) has been linked to several neurological conditions.

Goal(s):  Our aim is to develop a method combining contrast media administration, MRI, and postprocessing for detailed study of the glymphatic system in rats.

Approach: We investigated how administration routes with various invasiveness effect the distribution of contrast agent (CA) in the healthy rat brain and compared different data analysis methods.  

Results: Only cisterna magna application showed satisfying results. Time series cluster analysis shows patterns in the contrast agent distribution dynamic. 

Impact: A reliable MRI-based method for investigating the glymphatic system in rats will allow for the study of its role in several neurodegenerative and other diseases.

Keywords: Biology, Models, Methods, Neuroscience, Modelling, new device, hippocampus

Motivation: Virtual brains are proving quite successful for BOLD signal simulation but they still lack a specific mathematical description of individual brain regions.

Goal(s): Our goal was to develop a specific mean field model (MF) of the hippocampus CA1 microcircuit.

Approach: A bottom-up formalism recently developed for the cerebral and cerebellar cortex was adopted. It is based on a transfer function, which remaps neuronal microscale features from cellular recordings to the mean field mesoscale domain.

Results: The hippocampus CA1 MF reproduced the neuronal activity of the microcircuit and captured learning mechanisms.

Impact: The mean field of the hippocampus CA1 microcircuit enriches the growing collection of region-specific models. Its forthcoming integration into virtual brains together with other region-specific models has the potential to achieve a comprehensive and personalised BOLD signal dynamics simulation.

Keywords: Neurotransmission, Metabolism, Glucose, glutamate, GABA, Neurons, neurotransmission

Motivation: Fasting is used in weight loss but its impact on brain activity is not well understood.

Goal(s): To assess the impact of prolonged fasting on the excitatory and inhibitory neurotransmission in the brain.

Approach: Infuse [1,6-¹³C₂]glucose in mice fasted for 4h to 60h, and measure ¹³C labeling of brain metabolites by ¹H-[¹³C]-NMR spectroscopy.

Results: The glutamatergic neurometabolic activity was reduced in the cerebral cortex of mice fasted for 60 h.

Impact: These findings can be used for modifying the fasting paradigm in different interventions involving fasting.

Keywords: Large Animals, Nonhuman Primates, Animals

Motivation: Establishing standard brain images for various mammalian species may be useful in brain imaging analysis.

Goal(s): The current research aimed to establish a foundation for brain image analysis tools in a variety of mammalian species, including cats and marmosets, for which standard brain data are scarce.

Approach: For each species, we attempted to create an image of average brain using a nonrigid transformation algorithm. We also evaluated the quality of the average brain images by changing the number of subjects.

Results: We were able to create an image the average human, cat, marmoset, and mouse brain based on T1- and T2-weighted images.

Impact: This study provides an important foundation for the creation of standard brain images of various animal species and for the evaluation of individual differences. 

Keywords: Software Tools, Software Tools, preclinical, MRSI, spectroscopy

Motivation: Numerous software options exist for MRS processing, yet the preclinical domain lacks a harmonized multimodal toolbox featuring a graphical user interface (GUI).

Goal(s): Our goal was to create a harmonized toolbox tailored to preclinical MRS processing, with a special focus on addressing MRSI-related challenges.

Approach: The MRS4Brain Toolbox was designed to handle 1H and X nuclei data, and to allow brain segmentation of MRSI voxels in order to investigate brain regional differences.

Results: Fast and user-friendly brain MRSI segmentation and metabolic mapping were achieved, promoting the study of brain-regional differences.

Impact: The implementation of the open-source MRS4Brain Toolbox enables rapid and straightforward advanced preclinical MRS(I) data processing and quantification. It falls in line with the within- and across-site standardization effort launched by the MRS community. 

Keywords: Epilepsy, Hyperpolarized MR (Non-Gas)

Motivation: Thirty percent of epilepsy patients have seizures despite best medical therapies. Therefore, a non-invasive method to localize seizure onset zone (SOZ) and epilepsy network (EN) in epilepsy surgery to improve surgical outcomes is essential.  

Goal(s): The goal of this study was to apply dynamic magnetic resonance spectroscopic imaging (MRSI) of hyperpolarized [1‑¹³C]pyruvate (Pyr) to measure lactate (Lac) release in a Pentylenetetrazol (PTZ) mouse model of epilepsy.

Approach: We hypothesize that hpMRSI of [1-¹³C]Pyr accurately measures elevated Pyr-to-Lac conversion in a PTZ mouse model of epilepsy.

Results: Significant increase in Pyr-to-Lac conversion has been measured in PTZ kindled mice compared to control mice.

Impact: Epilepsy surgery outcomes depend on correctly identifying SOZ and EN. We utilized hpMRSI of [1-¹³C]Pyr to accurately identify elevated Lac release in PTZ mouse model of epilepsy. These results support its potential application to identify epileptic focus in epilepsy patients.

Keywords: Small Animals, Spectroscopy, X-nuclei, dynamic 13C, mice brain, cerebral metabolism

Motivation: Dynamic ¹³C MRS is a powerful tool for the investigation of brain metabolism in vivo. Due to its low SNR, it is typically constrained to big voxel sizes covering almost the whole brain in mice. Thus, making region specific research questions difficult.

Goal(s): Investigating the feasibility of acquiring ¹³C spectra from a distinct brain region (bilateral hippocampi) in the mouse brain at 9.4T.

Approach: We applied a combination of polarization transfer, a CryoProbe, frequency correction and ‘SVD denoising’ for the acquisition of ¹³C spectra.

Results: We achieved sufficient spectral quality to quantify even small metabolite pools like GABA in the bilateral hippocampus.

Impact: 13C MRS of distinct brain regions in the mouse brain paves the way for more specific research questions.

Keywords: Biology, Models, Methods, Neuroscience, fMRI Analysis, brain connectivity, preclinical

Motivation: We do not yet know where zona incerta (ZI) neural activity is distributed in central pathways despite extensive knowledge of incertal projections and functions.

Goal(s): We aim to reveal the long-range functional pathways of ZI neural activity to bridge the knowledge gap between known anatomical projections and implicated functions.

Approach: We deployed optogenetic fMRI to directly initiate neural activity at ZI and computational approaches to characterize the downstream central pathways involved.

Results: The propagation of neural activity from ZI are not restricted to monosynaptic projections within known subcortical structures, but along multi-synaptic, long-range central pathways.

Impact: Characterization of ZI functional pathways is of tremendous value to neuroscientists and clinicians for future in-depth investigations of key/previously undefined incertal regions and for designing more effective therapeutic measures such as deep brain stimulation, where ZI is a key target.