Young plasma administration mitigates depression-like behaviours in chronic mild stress-exposed aged rats by attenuating apoptosis in prefrontal cortex.

Brain ageing alters brain responses to stress, playing an essential role in the pathophysiology of late-life depression. Moreover, apoptotic activity is up-regulated in the prefrontal cortex in ageing and stress-related mood disorders. Considerable evidence suggests that factors in young blood could reverse age-related dysfunctions in organs, especially in the brain. Therefore, this study investigated the effect of young plasma administration on depressive behaviours in aged rats exposed to chronic unpredictable mild stress (CUMS), with a focus on the apoptosis process. Young (3 months old) and aged (22 months old) male rats were randomly assigned into four groups: young control (YC), aged control (AC), aged rats subjected to CUMS (A+CUMS) and aged rats subjected to CUMS and treated with young plasma (A+CUMS+YP). In the A+CUMS and A+CUMS+YP groups, CUMS was used to generate the depression rat model. Moreover, the A+CUMS+YP group received pooled plasma (1 ml, intravenously), collected from young rats, three times per week for 4 weeks. Young plasma administration significantly improved CUMS-induced depression-like behaviours, including decreased sucrose consumption ratio, reduced locomotor activity and prolonged immobility time. Importantly, young plasma reduced neuronal apoptosis in the prefrontal cortex that was associated with reduced TUNEL-positive cells and cleaved caspase-3 protein levels in the A+CUMS+YP compared with the A+CUMS group. Young plasma can partially improve the neuropathology of late-life depression through the apoptotic signalling pathways.