Although findings from both animal and clinical research indicate that the blood-brain barrier (BBB) contributes to the pathogenesis of various psychiatric disorders (including depression), the underlying mechanisms are unknown. We investigated the levels of the tight-junction proteins claudin-5 and aquaporin-4 (AQP-4) in astrocytes of learned helplessness (LH) rats (an animal model of depression) and non-LH rats (a model of resilience).

These results suggest that LH rats but not non-LH rats experienced down-regulations of claudin-5 and AQP-4 in the CA-1 and CA-3. It is possible that a region-specific modulation of claudin-5 and AQP-4 is involved in the mechanisms of vulnerability but not resilience in depression.

We administered inescapable mild electric shock to rats and then identified the LH and non-LH rats by a post-shock test. The expressions of claudin-5 and AQP-4 in several brain regions of the LH and non-LH rats were then evaluated by a western blot analysis.

The levels of both claudin-5 and AQP-4 in the CA-1 and CA-3 hippocampal areas of the LH group were significantly lower than those of the control group, whereas those of the non-LH rats were not significantly different from those of the control and LH rats. Conclusions: These results suggest that LH rats but not non-LH rats experienced down-regulations of claudin-5 and AQP-4 in the CA-1 and CA-3. It is possible that a region-specific modulation of claudin-5 and AQP-4 is involved in the mechanisms of vulnerability but not resilience in depression.