Sleep-related Brain Activity in an Arousal-reducing Agent-induced Mouse Model Evaluated with fMRI

Functional MRI (fMRI) has been established as a technique for capturing functional changes based on brain activity and is widely used to evaluate various diseases and physiological conditions. However, studies that systematically evaluate functional brain networks during arousal-reducing agent-induced sleep in mice by using resting-state fMRI (rsfMRI) are limited. This study aimed to compare and analyze whole-brain functional connectivity (FC) and reorganization patterns of large-scale brain functional networks in the mouse brain during arousal-reducing agent-induced sleep, focusing on arousal-reducing agents acting on different arousal regulatory systems.

Sixteen healthy male C57BL/6JmsSlc mice (aged 16.4 ± 8.7 week) were used in this study. The mice were assigned to 4 groups: control, zolpidem (20 mg/kg), lemborexant (40 mg/kg), and dexmedetomidine (75 μg/kg). rsfMRI was performed using a 9.4T MRI system equipped with an 86 mm volume transmit coil and an 8-channel receive-only coil (Bruker BioSpin, Ettlingen, Baden-Württemberg, Germany). After head post-surgery and habituation, blood oxygenation level-dependent (BOLD) images were acquired using a gradient-echo echo-planar imaging (GRE-EPI) sequence (TR/TE = 1500/14 ms). Each mouse underwent six 10 min imaging sessions. fMRI data were preprocessed using Statistical Parametric Mapping (SPM12; Wellcome Centre for Human Neuroimaging, London, UK) and analyzed using the CONN FC toolbox (McGovern Institute for Brain Research, Massachusetts Institute of Technology, Cambridge, MA, USA). ROI × ROI FC matrices were calculated for each fMRI session. Group differences were assessed using linear mixed-effects models that accounted for repeated measurements within animals, individual variability, and age differences among groups.

Compared to the control group, the zolpidem group showed the smallest overall differences, whereas the dexmedetomidine group showed the largest differences. Furthermore, although relatively similar trends were observed between the groups in the distribution of mean correlation coefficients within each network, different trends were observed between the networks.

In addition to network reorganization associated with the sleep-inducing state, which is commonly observed regardless of the arousal-reducing agent type, distinct network changes exhibiting arousal-reducing agent-specific connectivity patterns were observed.