Anxiety-like behaviors in pre-pubertal rats of the Flinders Sensitive Line (FSL) and Wistar-Kyoto (WKY) animal models of depression

Animal models have been used in understanding the neuro-biological basis of depression and predicting successful treatment strategies. The current study focused on two genetic models of depression, the Flinder's Sensitive Line (FSL) and Wister-Kyoto (WKY). Our laboratory showed depressive symptomatology in pre-pubertal WKY and FSL rats, and the current study focused on the strains' anxiety-like traits. Since human depression-anxiety comorbidity is very common at young ages, it is essential to establish whether FSL and WKY pre-pubertal rats also exhibit such comorbidity. In addition, the effect of different rearing environments was studied using a mild chronic-stress condition (limiting available bedding between post-natal days 2-9). Two well-validated tests of anxiety, the open-field and elevated plus-maze, were used on 40-day-old pups. FSL pups exhibited lower anxiety-like behavior when compared to controls, in traditional open-field and plus-maze measures. A different pattern was observed in the WKY strain, which exhibited heightened anxiety-like behaviours in the FSL strain and affecting WKY's body-weight. Overall, the findings indicate differential expression of anxiety in pre-pubertal rats belonging to the 'depressed' strains, suggesting that these strains may be suitable for modelling different sub-groups of depression at young ages.