Evolution of brain-wide activity in the awake behaving mouse after acute fear by longitudinal manganese-enhanced MRI

Abstract

ELB) 26 27Key words: (at least 5) 28Magnetic Resonance Imaging, neuroimaging, statistical parametric mapping, serotonin transporter 29 knock-out mouse, predator stress, innate unconditioned fear, anxiety, mouse models 30 31Running title: Evolution of neural activity from fear to anxiety 32 33 34 2 Abstract 35 Life threatening fear after a single exposure evolves in a subset of vulnerable individuals to anxiety, which 36 may persist for their lifetime. Yet neither the whole brain's response to innate acute fear nor how brain 37 activity evolves over time is known. Sustained neuronal activity may be a factor in the development of 38 anxiety. We couple two experimental protocols to obtain a fear response leading to anxiety. Predator stress 39 (PS) is a naturalistic approach that induces fear in rodents; and the serotonin transporter knockout (SERT-40 KO) mouse responds to PS with sustained defensive behavior. Behavior was monitored before, during and at 41 short and long times after PS in WT and SERT-KO mice. Both genotypes responded to PS with defensive 42 behavior, and SERT-KO retained defensive behavior for 23 days, while wild type (WT) mice return to 43 baseline exploratory behavior by 9 days. Thus, differences in neural activity between WT and SERT-KO at 9 44 days after PS will identify neural correlates of persistent defensive behavior. We used longitudinal 45 manganese-enhanced magnetic resonance imaging (MEMRI) to identify brain-wide neural activity between 46 behavioral sessions. Mn 2+ accumulation in active neurons occurs in awake behaving mice and is 47 retrospectively imaged. To confirm expected effects of PS, behavior was monitored throughout. Following 48 the same two cohorts of mice, WT and SERT-KO, longitudinally allowed unbiased quantitative comparisons 49 of brain-wide activity by statistical parametric mapping (SPM). During natural behavior in WT, only low 50 levels of activity-induced Mn 2+accumulation were detected, while much more accumulation appeared 51 immediately after PS in both WT and SERT-KO, and evolved at 9 days to a new activity pattern at p<0.0001, 52 uncorr., T=5.4. Patterns of accumulation differed between genotypes, with more regions of the brain and 53 larger volumes within regions involved in SERT-KO than WT. A new computational segmentation analysis, 54 using our InVivo Atlas based on a manganese-enhanced MR image of a living mouse, revealed dynamic 55 changes in the volume of significantly enhanced voxels within each segment that differed between genotypes 56 across 45 of 87 segmented regions. At Day 9 after PS, the striatum and ventral pallidum were active in both 57 genotypes but more so in the anxious SERT-KO. SERT-KO also displayed sustained or increased volume of 58 Mn 2+ accumulation between Post-Fear and Day 9 in eight segments where activity was decreased or silenced 59 in WT. Staining of the same mice fixed at the conclusion of imaging sessions for c-fos, a marker of neural 60 activity, confirmed that MEMRI detected active neurons. Intensity measurements in 12 regions...

Accelerating in vivo fast spin echo high angular resolution diffusion imaging with an isotropic resolution in mice through compressed sensing

“…Manganese enhanced MRI and volumetry have been used as quantitative measures instead, [87][88][89][90][91][92] but neither can be used to investigate brain wide structural connectivity, and manganese enhanced MRI is more invasive. fMRI has been applied in the amygdala, 93,94 and recently fMRI of the entire olfactory system has been achieved, 95 which would be complemented by the technique presented in this research.…”