Hair growth predicts a depression-like phenotype in rats as a mirror of stress traceability

As a subjective mood-related disorder with an unclear mechanism, depression has many problems in its diagnosis, which offers great space and value for research. At present, the methods commonly used to judge whether an animal model of depression has been established are mainly by biochemical index detection and behavioral tests, both of which inevitably cause stress in animals. Stress-induced hair growth inhibition has been widely reported in humans and animals. The simplicity of collecting hair samples and the observable state of hair growth has significant advantages; we tried to explore whether the parameters related to hair growth could be used as auxiliary indicators to evaluate a depression model in animals. The length and weight of the hair were calculated. Correlation analysis was conducted between the depressive behavioral results and the glucocorticoid levels in hair and serum. Learned helplessness combined with chronic restraint stress, and chronic unpredictable stress in the animal were detectable by superficial observation, weight ratio, and length of hair, and follicular development scores were significantly reduced compared to the control. The hair growth parameters of rats with depression, the rise in corticosterone, and the corresponding changes in behavioral parameters were significantly correlated. The neurotrophic factors, glucocorticoid-receptor (GR), brain-derived neurotrophic factor (BDNF), fibroblast growth factor 2 (FGF2), and fibroblast growth factor 5 (FGF5), are associated with depression and hair growth. Significant differences were detected between the stress and control groups, suggesting that the mechanism underlying the stress-phenomenon inhibition of hair growth may be related to growth factor mediation.