Mice overexpressing corticotropin-releasing factor show brain atrophy and motor dysfunctions

Abstract

Chronic stress and persistently high glucocorticoid levels can induce brain atrophy. Corticotropin-releasing factor (CRF)-overexpressing (OE) mice are a genetic model of chronic stress with elevated brain CRF and plasma corticosterone levels and Cushing's syndrome. The brain structural alterations in the CRF-OE mice, however, are not well known. We found that adult male and female CRF-OE mice had significantly lower whole brain and cerebellum weights than their wild type (WT) littermates (347.7+/-3.6mg vs. 460.1+/-4.3mg and 36.3+/-0.8mg vs. 50.0+/-1.3mg, respectively) without sex-related difference. The epididymal/parametrial fat mass was significantly higher in CRF-OE mice. The brain weight was inversely correlated to epididymal/parametrial fat weight, but not to body weight. Computerized image analysis system in Nissl-stained brain sections of female mice showed that the anterior cingulate and sensorimotor cortexes of CRF-OE mice were significantly thinner, and the volumes of the hippocampus, hypothalamic paraventricular nucleus and amygdala were significantly reduced compared to WT, while the locus coeruleus showed a non-significant increase. Motor functions determined by beam crossing and gait analysis showed that CRF-OE mice took longer time and more steps to traverse a beam with more errors, and displayed reduced stride length compared to their WT littermates. These data show that CRF-OE mice display brain size reduction associated with alterations of motor coordination and an increase in visceral fat mass providing a novel animal model to study mechanisms involved in brain atrophy under conditions of sustained elevation of brain CRF and circulating glucocorticoid levels.

Fig. 1

Brain size difference (A) and weight (B-E) of WT and CRF-OE mice. Bars represent mean ± SEM of number indicated at the bottom. **p<0.001 vs. WT.

Fig. 2

Size of representative brain areas in female CRF-OE and WT mice (n=5/group) in Nissl stained sections. Brain structure size was evaluated using NIH image J version 1.42. Neocortex (dashed line) and cingulate cortex (full line, A) as well as the paraventricular nucleus of the hypothalamus (D) were significantly smaller in CRF-OE (B, E) compared to WT littermates (A, C, D, F). * p<0.05; ** p<0.01 and *** p<0.001 vs. WT.

Fig. 3

Motor performance and gait analysis in female CRF-OE mice (n=8-10) and WT littermates (n=12). CRF-OE mice showed a significantly longer time to traverse the beam (A), significantly more steps on the beam (B) and made significantly more errors/step (C). Stride length in CRF-OE was significantly smaller compared to WT (D) whereas the maximum stride difference (E) and width (F) were not changed * p<0.05 and ** p<0.01 vs. WT.