Heterochronic Parabionts

As people age, their cognitive ability inevitably declines. The scientific community has attempted to explore factors that could prevent—or at the very least improve—this cognitive decline. In particular, Villeda et al. conducted a series of experiments in order to determine the relationship between young blood and cognitive functioning. Specifically, they surgically connected old mice to young mice to form heterochronic parabionts, and old mice with other old mice to form isochronic parabionts. This process of parabiosis ensured that the blood from both constituents would mix together, producing a mixture of either old and new blood or old and old blood. After conducting multiple diverse experiments, the scientists noted some significant findings. In one experiment, the scientists utilized Golgi analysis to
In fear conditioning, after repeated trials, mice eventually came to associate a fear conditioning chamber with a shock. Since it has been established that contextual fear conditioning, such as this task, requires the hippocampus, this task was used to test the effect on the hippocampus after the addition of young blood to the mice’s system. Whether or not mice learned the association was determined by measuring freezing time, or the amount of time they stood still. The results indicated that heterochronic parabionts excelled in these tasks. Villeda et al. also designed a fear conditioning experiment to test the involvement of the amygdala; in contrast, in this test, the mice learned to associate a shock with a visual and audio cue. However, the results from this task indicated that heterochronic parabionts did not perform better on these tests. This verified that young blood resulted in changes in the hippocampus rather than other parts of the brain, such as the