Notably, the outcome of heterochronic blood exchange is also different from heterochronic parabiosis, particularly for neurogenesis where our results suggest that old blood is far more inhibitory to tissue health than that young blood is rejuvenative, and that peripheral tissue injury compounds the negative effects of old blood on young neurogenesis.

I need to pick through the methodology more, but it is an interesting finding if old blood has more potent negative effects than young blood does positive.